Technically speaking, "Scavenging" is just the process of venting the exhaust from the cylinder and drawing in a fresh intake charge, what I talk about in this video is more Pressure wave or Harmonic Scavenging. There is also a bit to be said about gas velocity in the runners, but this video was already getting too long. Also, minor correction - at 3:30 I meant to say "combustion products" not "unburnt gasses" Thanks for watching!
Excellent channel, I've just found and subscribed! Another very pedantic point, you say 'heat' when you mean 'temperature'. Yourself and many of your viewers will know the difference, but just thought I ought to mention.
C Sbastianygaumnitz it can smoothed out in a dyno tune. Or flap inside the exhaust you can control. I like to dyno exhaust changes. but who likes paying money each time you change Lol?
I have watched countless videos about this subject trying to wrap my head around this concept and even theorized that a tuned exhaust could only benefit a certain rpm or multiples of that RPM/frequency just like notes in music complement each other others while other clash. Thank you for this video. It really helped bring it all together and and explain how back pressure plays a roll.
Great video. This is especially important on rotary engines. The main reason all pre renesis (RX8) engines gained huge amounts of power after putting a free flowing exhaust system on is because the factory exhaust system was the cause of excessive back pressure, once you put a larger free flowing exhaust system you saw anywhere from 20-30 % power increases. Unfortunately the renesis engine sees very little if any power increases (sometimes 5-10 kws if you are lucky) with an exhaust system upgrade because the side exhaust ports are the cause of the restriction in the exhaust.
Hey, I own a 99 GT Mustang. In 2013 I installed a pair of Flowmaster super 44 because of the " back pressure". Now, in January I installed a pair of Dynomax UltraFlo. That's a direct flow and, wow, the difference is huge. I can't talk about armonic or whatever, I can talk about the difference in power and response of that engine. Somenthing that I can feel.
@@pizzaguy58 , without redoing the entire video, because this man's understanding of the terminology he's trying to speak of his inadequate for what he was trying to explain, I have to let you understand that a Flow Restriction it's not intentionally put into exhaust systems. It's usually an effect of an engineering anomaly. Exhaust Scavenging is done by tuning the exhaust so that adjacent cylinders are always drawing air and trying to keep the exhaust pressure as low as possible when the valves are in an overlap condition. Scavenging is best done by tuning the exhaust system so that the exhaust gases are at their lowest pressure in the manifold so that they don't cause a reversion up into the intake or as little as possible, when the valves are in a condition of overlap. At no time did I suggest that I Flow Restriction will not cause back pressure. But flow Restriction has not been intentionally designed in cars since the late seventies I think when they still had the heat risers on the right side manifold that would choke off the exhaust on the right side and force it underneath the carburetor to warm the engine up a little quicker. Some flow restrictions have been put into cars by accident or incidental misunderstanding of wave Dynamics. Any time an exhaust pipe is longer than 3 feet it starts to draw power from the engine because it starts to cause a problem with the way wave Dynamics occur inside a long straight piece of pipe. It is also why you have different size exhaust pipes built on to larger displacement engines because flow velocity has to be maintained in order to provide Scavenging to the individual cylinders. And there is no internal combustion engine that is perfect at that. The limitations of design require that there's going to be some pressure within the exhaust that is going to be higher then on the intake side of a cylinder because that's just the nature of the Beast. So I think you understand now the difference between Flow Restriction and exhaust back pressure fit is not necessarily designed into the engine but it doesn't affect of the fact that it can never be done completely away with. And I think the confusion comes in the fact that exhaust back pressure is piss poor terminology.
I see what you’re saying now, I misunderstood in the first comment. So then what would cause flow restrictions in a regular naturally aspirated exhaust? I thought you were referring to the restriction of flow through the sound muffling in the system. When I think of back pressure I think of anything that resists the flow, which I would think flow restrictions would be included in that. Am I wrong in that thinking?
@@pizzaguy58 only from a technical understanding. But it helps to be accurate so that you don't conflate your terms. This was not a good video for the explanation because the person doing the video was not aware of the proper terminology himself. At least not all of it. I've seen reversion so pronounced that it actually creates a fog above the carburetor when you're racing on a dirt track or even an oval track.
This topic should be more discussed, would love to see more info from this guy about header diameter/lenght, different cone/spike shapes that close the headers end section and such
Excellent way to explain the concept at all, Im some one who knows nothing about engines, despite of this I have fully understand the concept, Awesome, thanks!.
@@s.lacasse8337 my mk1.5 MR2 has essentially an open 3" from the turbo back. Fantastic spool, great hp/tq, bit loud. Fabricating an exhaust right now that has a cutout that splits into a 3" extra quiet muffler and rejoins to a single exit. Silent mode -> race mode with the same 3" tip
You made a very informative video. What I learned is with an n/a motor, you should buy a well engineered exhaust system. And for a turbo car, just cut all the exhaust off or run as big as possible.
EXACTLY. That's literally how long the video needed to be. This "exhaust backpressure is good for performance" stuff needs to die a terrible, terrible death. 11 minute meandering explanations don't help that at all.
You explained things very well, however when you said engines will 'need backpressure' you should have rephrased it as a tuned system will result in some backpressure in the unoptimized area in the power band(which you sort of said). Otherwise well done and Ive been saying the same stuff for years and its nice to have a video I can link to save my breath lol
setting the overlap of the cam and cam timing is everything,but the exhaust design also adds to the scavenging,hence expansion chambers on race two strokes,some of the changes were dramatic to say the least,there are people in the industry that can give you what you want in design for your specific rpm range
with 2.75-inch straight piping and a regular normal muffler I got a skyrocket rpm boost from 5k rpm to 7500rpm on my d15befi non vtec it feels wow at that rpm band point my experience helped me understand your explanation also good amount of torque is available at lower rpm also
There are quite a few points you have missed here, drag cars with cross plane cranks don't use venturi based scavenge effects like a flat plane cranks due to the different firing orders, the reason they don't use a collector mostly is because the scavenge is not really working in a V8 cross plane crank engine. A flat plane crank like found in Ferrari engines for example can utilise a proper collector for exhaust scavenging effects, but these engines also have inherent vibrational issues as a trade off. Pressure wave pulses work better from log manifold that that of collectors, but log does not scavenge using venturi vacuum and high velocity, scavenging using a venturi effect is better in a collector exhaust system and a higher exhaust velocity is essential to help even further, this is why a proper gauge exhaust tube is required for each engine to keep velocity high. The turbo charging exhausts love a huge exhausts for your explained reasons. I had a twin turbo GTR a few years back making 500AWKW with twin 2863's on it and the amount of restriction in the exhaust housing was so great I had to use 33psi just to push against it. Also the twin turbo's run out of puff with LPM in the intake manifold compared to larger single turbo. I should have gone with the larger single in the end to keep the LPM's up and use a lower boost pressure to achieve the same power. Having such large boost intake pressures was not easy, the coolant temp levels were around 127C at some points around the 5th lap mark on track. Obviously with pressure came heat and probably the most significant issue was the huge amount of pre turbine back pressure issue that would have been keeping exhaust gasses from escaping properly, I was well and truly pushing the limit of twin turbo's to levels I really shouldn't have been for the given power levels. I could have cooled it more with better cooling systems, but at the end of the day, it was the poor little turbos that needed to swapped out for a larger, better flowing single. Damn it had some crazy driving response though, it was an absolute weapon. Good video Kyle, keep em coming mate, peace out from Perth.
nice video! thanks! it gave me some additional info about this subject. i was first misleaded by the title, because i couldn't believe that an 4stroke-engine really likes to see backpressure at the exhaust. but having watched your video, i understand what you wanted to point out.
Good vid. Probably helped a lot of people. I would say that the content is pretty low complexity to moderate at best. --A lot of people confuse what "Back pressure" is. There is no back pressure until the engine is running. Sound stupid, but basically back pressure is the result of engine dynamics. There is no reason for back pressure at all. Now, some people will call the pressure differential between exhaust port output and turbo exhaust intake as back pressure. I can see why, and whatever. But, beyond the turbo exhaust out, there is no reason for any back pressure. The only reason, to my understanding, why there is even an exhaust at all on a vehicle to to quiet it down and pass emission standards.
it'd be awesome if you could do a video just on n/a engines, (optimal intake pressure, temperature and resonance??) as well as more on exhaust pressures and design in race applications! I am looking to design a custom intake and exhaust system for an n/a engine (ej25 to be specific) to be used for racing, and am thinking of cooperating with bodywork for both the intake and exhaust. I'm wondering if designing an exhaust with similar properties used in diffusers (lower pressure at the exit) would effectively create a sucking effect on the exhaust? very interested to hear more about n/a!!
Thank you for the very informative talk. Can you address a few question I have about turbos in a future video? I want to know how much of the airflow the exhaust side of the turbine captures as it exits the engine. And what the turbine is doing when there is no effective boost. Or, does it always provide a small amount of boost? I understand that when the vacuum reaches maximum on engine over-run, the fuel is cut, and only air is passing through the engine - using its compression to act as a brake - is that right? What 's happening to the turbo on over-run? Does it stop, or just slow down? What would be the minimum sort of speed a turbo spins, with the engine simply idling? When I get into the gas, but limit the boost to 0 psi, does that represent the maximum power the same engine without a turbo would make? (Or very close to it, due to the internal drag of a non-boosting turbo.) What happens in the turbo housing when I get to peak turbo boost? Is the wastegate opening just enough to maintain the pressure on the outlet side of the turbo? I have a very small turbo on my old Tommy Kaira M20b, and I wonder what sort of revs it might hit at 10psi boost- would you hazard a guess? It makes some wicked sounds! What happens to the revs of the turbine once the wastegate begins opening? Does it stay constant?
In all exhaust system, there is an expansion chamber in the form of a middle drum with no baffles, generally with 15 times cylinder sweep volume to allow the exhaust gas to expand sufficiently to maintain a stable anti-node and much reduced back pressure (near ambient) such that variation of pressure in the silencer system does not affect the header system much, this is more important for a tuned header, however, addition of a catalytic converter generally creates a significant back pressure while obviously being a stable node in the acoustic system of the header.
Air planes have tuned exhaust and zero expansions until the end of the pipe. So i disagree that all systems have this middle drum. Thinking of it the only expansion chambers I have seen are on 2 strokes.
I wish the term "backpressure" would die. Invariably when people advise you "don't go too big or you'll lose backpressure", what they really mean is exhaust gas velocity. As Bernoulli tells us, a fluid traveling at a higher speed is a lower pressure. Therefore by going to a smaller diameter exhaust, you are (increasing velocity and) actually losing pressure, which humorously is the opposite of what they claimed would happen.
MrClown indeed. usually when people go big, and thus the exhaust loses velocity it tends to bounce around and stack up and can result in increased BP. Proper built race cars run disturbingly small pipes and make killer power.
MrClown That's one aspect. Another is the reduced static pressure at the port due to the momentum of the previous exhaust stroke. It's easy to forget that for a while, the exhaust is flowing down a closed cavity, and this means that significant momentum in that flow can allow it to draw a low pressure zone in the pipe behind it, ready to aid the subsequent blow down event. This is the single most important factor when deciding which cylinders to connect in double or triple Y collectors.
There's a range of effective exhaust tubing diameter that will increase velocity, but not to the point of reducing efficiency of the system, i.e. going too small. In other words, there is an optimal size for a given system. Too small and too big create problems on either side. Flow dynamics are an interesting science.
I remember the last time a had a icy smoothie the bigger the straw the bigger gulps I had and the easier it was to get it out, but in a small straw fucking turned into a sucking workout!
dig the channel dude. Quick question what's your opinion on why drag car zoomies (straight out pipe no collector) don't have a bell mouth or trumpet funnel arrangement on the discharge. Ps to anyone else reading, don't skip the adds and click the add links and likes so this bloke can get something back for the effort he's putting in. I bet he paid a lot for his engineering lessons i'm happy to pay 20 seconds for mine.
It is not an anti node rarefaction of a standing wave, it is an expansion wave that is reflected from an initial compression wave that is created by the sonic (speed of sound) gas flows just as the valve or port opens which rapidly drops to sub sonic flows in the exhaust, while the compression wave continues at the local sonic velocity of the gas in addition to the velocity of the gas, when compression wave meets an increase in pipe area (outlet or collector inlet) of any kind it reflects a mirror copy of itself as an opposite pressure signed expansion wave that travels back up the exhaust pipe at the local sonic velocity minus the forward gas velocity. The expansion wave is timed to return during valve overlap, that is determined by the length of the pipe from the valve to an increase in area which is the distance the wave will travel and negative wave will return know as "tuned length". If the time the waves take to traverse that distance in the pipe, determined by local sonic velocity (speed of sound) in a gas, is the same amount of time as the exhaust open to inlet open occurs at a given RPM, then the expansion wave will draw more intake in then would be the case by mere pumping. I have a bunch of videos on the topic mostly 2 stroke and one recently on inertial scavenging and how it compensates pumping losses of the piston rising after BDC in a 4 stroke.
AuMechanic I've seen moto3 bike with single cylinder with dual exhaust (one outlet per valve design), does this amplify the return wave strength thus increasing engine volumetric efficiency at a specific rpm range?
@@soraaoixxthebluesky Yes it probably does, also keep in mind that the tapered cone shape at the end of the exhaust pipe (called a megaphone) has the function of making the reflected expansion wave effective over a wider RPM range than a straight pipe outlet is limited to, something this video failed to mention, a note a properly designed 4 into 1 exhaust will also have a taper section after the collector for the same reason.
Liked it ! When i took my catalitic converter out, it actually made it worse....started to loose power at high rpm, and the top speed dropped....also the mid rpm torque dropped.....
That's why for a N/A engine you need "Tuned Length headers" for your displacement/cam timing. Shorty header only save weight and give no/very little power on a current OHV V8.
You're somewhat close with the resonant tuning, but you're missing a major point. The cylinder still has a bit over 100psi in it when the valve is opened. This is... massive... compared to any other pulse tuning pressure in the car. The result is that about half the residual gas leaves the cylinder before the piston has moved up any significant amount. The ideal negative pulse arrival time (at the valve) is top dead centre. If tuned correctly you can end up with negative 4psi (gauge) in the cylinder when the intake valve opens. This is why overlap is so important on a race car, and why cam specs influence header design. The major effect is on the same cycle, not the next Look at this graph musclecardiy.com/wp-content/uploads/2015/01/8.jpg and note that peak vacuum occurs fractionally before tdc. and download the "engine analyzer" demo from performance trends to see the effect and data of tuning exhausts. Try a 40" primary pipe on the demo engine and see what happens when you get the full action of the 1st reversion pulse
Skippy cheers I appreciate it I have a 4litre 1grfe petrol engine and I have just bought and on Friday will be installing long tube genie headers and removing 2 out of the 4 cats with a stock ecu is it still possible to get good Benefits and is it possible for scavenging to still happen?
@@jamier9113 I just had a look at that. I'm assuming you have a hilux. They have pretty poor manifolds that look like a pipe bolted to the head, so literally anything is an improvement. Half of manifold design is eliminating screwups. Genie looks like they eliminated the biggest screwup of having mitred joins. Incidentally so did Toyota with other apparently interchangeable headers. By removing the cat converters you have also improved flow. Between those two things (having real bends and having less cat converter to deal with) there will be significantly less residual pressure in the exhaust ports, so you'll have a much better situation at overlap. You'll probably gain, I'm gonna guess, 5% under any given condition. This is basically avoiding screwups. As for real scavenging (making something genuinely good) I don't think it's going to work. They aren't long enough to get the acoustic tuning right. They are also probably too large for inertial tuning (which to a degree sucks the exhaust out once the above mentioned blowdown pulse gets things moving).The Genie headers are 44mm in diameter, ideal size for a 500cc cylinder at 4000-ish rpm is 28mm. I don't feel like doing the maths on the 1GR but I'd be surprised if they were supposed to be bigger than 35mm. I don't think for a second you've made a bad choice, there's every chance the Toyota exhaust port is too big to put a good header on it and there's probably not enough overlap to make the most of it even if you did
hey man, great video. can you do a video on the effects of having a vacuum in your crankcase (how/ if it helps with piston ring sealing and how/ if it helps with lubrication). Thanks a lot
Within tuned range, I don't agree that coupled exhaust will create sucking effect for next cylinder., at least not in time. Instead , it will have positive pressure when next cylinder starts opening exhaust valve, and travel to other cylinder. This positive pressure will reduce overall VE of the engine. Because it is able to cancel or reduce negative return pressure. However, it is depended on length, angle , diameter of the primary runners. Maybe this is the reason why drag car use individual exhaust runners.
shao jom drag cars and recing cars just focus on specific rpm band. Therefore they can design diameter and length just nice for that rpm. Normal everyday car needs to cater from low until high rpm (if possible) Therefore, scavenging helps in these low rpm region. However, I have not gauge any exhaust with a pressure meter. That would clear any myths.
It's not so much the wave speed within the exhaust but exhuast valve opening events. As the engine rpm (frequency) increases, the exhaust valve opening time (in seconds) decreases. With a fixed mean path length of the exhaust being fixed the opening events and the density wave go out of phase.
Good video however I strongly disagree with a comment you made a few times about scavenging not really being important or an issue for a turbo engine. Any opportunity allow a turbo engine to operate closer to an n/a engine should be capitalized on. Removing pre turbo emap allows you the potential to improve VE. As you know, Fluid dynamics dictate that fluid will flow from the higher pressure point to the lower. Creating a window for the engine to operate in where inlet to pre turbo exh pressure is under a 1:1 ratio, allows scavenging to take place if valve timing, fueling and ignition is optimized. This will absolutely help with turbo spool, off boost torque and drive ability, engine efficiency etc. Scavenging can and does work on turbo engines too.
Thanks for the great video, I put a gasket on the connection between the muffler and the exhaust pipe for a better sound. It can be said that this part of the exhaust is leaking now, will it damage the car engine in the long run or not?
Gasses have velocity and inertia. Pulse scavenging is more for two strokes. A smaller pipe will have higher velocity and inertia. Bigger will be lower but less backpressure but less inertia for scavenging on the overlap. Differences will have more or less power at different rpms. Now many motors have valve flaps down pipe in the exhaust to tune the inertia for all the rpm range.
I ran my exhaust on my 1995 S Series with a 1991-1992 GM factory header, a pace setter high flow cat converter and a factory muffler and the same size pipe. I also have a ported intake manifold , bigger throttle body a cold air intake, and totally upgraded suspension and a polyurethane master bushing kit, and although I'm gonna build it .20 over for a Turbo setup and dual intake cams, etc It has the perfect amount of torque, at the moment , back pressure for what it is. I don't have to even give it more than a third of a petal cruising and I look down at speedo, and I'm at 70-75 MPH in no time. But the car is only 2280 LBS with ample torque...lol It's gonna be downright nasty with 320-350 HP and RPF1 Einkei 15X7's and 205 50R 15 Toyo Proxies in the coming months...lol
At the end u do a muffler delete in turbo cars and all is well but only after u increase the boost otherwise leave it alone..my audi went fro 7 psi to 14 psi so I cut it off ..no problems..smooth
I am work in a vehicle workshop, this video is very helpful for me. Can I ask a question? we know at some car, there is a exhaust flap that close at low RPM to increase torque, and open at high RPM for reduced exhaust resistance. But how the torque increased by close exhaust flap?
I've just seen a video in which a fellow youtuber explained that in engines with 4 cylinders or more, exhaust pulses start to overlap, causing vortexes that decrease the efficiency of a turbo. Maybe you could make a video on that subject and go into a bit more detail ;-) Keep up the good work, mate! :-)
You are confusing the hell out of people by calling transient waves "back pressure" they are NOT, the overall actual back pressure does not change because of them. Also 5:20 you say a negative pressure should get to the exhaust port at valve opening. NOT so. The flow out the exhaust valve at that time is *choked* and no amount of suction down stream can affect that flow at all. The negative wave is timed to arrive at the exhaust at it's *closing* time and during overlap where it can pull out remaining exhaust and start pulling in fresh air from the intake. You are supposed to know this stuff.
Simply put, it is an input/output system. Efficiency (power) is the greatest when the system is in balance. Pull the exhaust off a stock engine and it will run terrible. You could retune to compensate but the engine will run rather inefficient outside of constant high rpm.
Obviously you aren't a drag racing guy, but if you could, I'd love for you to expand on the pros and cons of zoomies (isolated primaries) over collected headers. I've seen a few guys, when horsepower isn't an issue (as in tire limited classes where they have all the power they need but just have to figure out how to get it to the ground) prefer collected headers because they are "easier to tune". Im assuming its due to only requiring one o2 sensor per bank (therefore simplifying the data) as opposed to an o2 sensor per cylinder, but I'd love to know if I'm oversimplifying it, if I'm completely wrong, or if I'm on the right track but missing other variables. I understand this isn't your arena, but I'd appreciate the engineering/fluid dynamics view I think you may be able to provide. Thank you brother
Excellent video Kyle! Thanks for clearing up the myth about engines needing back pressure for so many uninformed folks. An ICE is basically an air pump. A working understanding of hydraulic circuit theory would quickly clear up the whole back pressure myth.
Hi have a question. I am making my car repaired and probably made some mistakes in exhaust system. Car is Jag x type v6 and both catalytics are broken - one emptied other is probably clogged. Car idles say for 3 mins then engine dies. Exhaust guy suggested me to place a universal catalytic where pipes from cats unite so there is now one catalytic on line before exhaust mufflers. After spark plugs replacement i can drive car for say 5 minutes then engine dies on the move, wait 10 minutes then car runs for another 5 minutes. So i think a big back pressure builds up and engine dies because there was not this issue before installing universal cat. I plan to remove new cat and let exhaust float easier until i find good cats. Thanks in advance. Cheers.
Hi Kyle.engineers, thank you for explaining the flow in the exhaust. I found this verry interesting. I stumbled upon you’re video as I was looking for a faultcode on my MB C class 180D 2015 model. The car has a fault code on the exhaust back pressure sensor (P047121A). I will replace the sensor, but what is actually the function of this sensor? Does this has anything to do with valve timing to reduce the backpressure (as this is a turbo charged car)? The fault comes up after overhauling the DPF (almost immediately) and I was wondering, why is this at this moment, what is the logic of that.
Interesting that a recent episode of Engine Masters showed that back pressure is undesirable for best performance and that the "smaller exhaust enhances torgue" idea is a myth. Dynamometer results were confirmation of free-flowing exhaust enhanced horsepower and torque both. Anti-reversion in both intake and exhaust were more effective. When I port and gasket-match intake and heads, I leave a. 030 anti-reversion "lip" on the intake port of the manifold and one on the exhaust port of the cylinder head. Power is enhanced as well as scavenging. My header design is optimized for 2,000- 3,500 rpm for daily drivers with different designs for performance engines based on the appropriate rev range. The port "lip" remains the same regardless. Between catalytic converter and muffler restrictions, there is plenty of backpressure. Post turbo scavenging is the same as you illustrate.
so in otherwords, increasing exhaust diameter will "shift" the power band up in the revs and decreasing it will give better low end? and in both cases straight pipe/laminar flow mufflers is the way to go; correct?
mas921 not necessarily, especially when the pulses is not interconnected, therefore no scavenging. And, when no scavenging, no harmonic scavenging aka 'supercharging effect' In other words, it have to be 'just nice', with your engine configuration, setup and tune. Just at the nice rpm that you targeted for.
Knight Fox The. I sub from this Chanel and go watch your EE. This guy does an excellent job at explaining and he dosent have newtlybthe time to practice as long as EE has been doing this.
I find EE to be better aimed at the novice viewer where Kyle explains better to those who already have some knowledge. EE also shows more math, but it's easy to gloss over that math if you don't understand what he's doing. Both have their pros and cons. It's good to watch both
This is called supercharging effect on intake and exhaust besides only siphoning and scavenging. Right Kyle? That's why complicated fluid designers and engineers went to variable length, variable route, and variable pressure restrictior to maximize the 'supercharging effect' of the intake and exhaust pulse, for as wider rpm bandwidth as possible
Where is the EGR valve in your drawing? The EGR takes exhaust gases and runs it through the engine again. Does that affect the back pressure? What happens to the exhaust with crossover pipes?
What would happen if there is a "back pressure " of only 800 /500 millibar or assume we have a wall and it it empties into a vacuum of several thousand m3(never have any back pressure ,always "sucking "out) ?
You could have added the factor of compression ratio or compression inside cylinder. Usually, the engines with EGR systems and no exhaust gas coolers have a lower compression ratio. In these cases, what would be the effect of reducing your exhaust backpressure?
Probably jumping the gun here at one third through the video, but there can’t be enough said for the effects of valve seats. It’s that split second as the seal is broken that creates crazy fast air speeds due to pressure differences. Trick multi (3+)angle cut valve seats are a real world upgrade. 🇦🇺🤜🏼🤛🏼🎅🏻🍀🍀🍀😎🤓
I’ve removed my catalytic converter on my turbo diesel truck and the engine runs smoother but I have lost some of the initial torque. It kicks in much later now..what can I do to get torque to kick in at a lower rpm
Since you are not altering the characteristics on the side that needs pressure/pulse waves for combustion chamber efficiency simply put, deleting the muffler (even the catalytic converter as well) on a turbo setup is generally BETTER for the system. Disclaimer - I AM NOT AN ENGINEER! This is what I've noticed from personal experience, a slightly educated guess at best so consult a professional lol.
This seems to be the consensus however my gut says if you free up one side of the turbine then your turbo can spool faster as there are less restrictions on exhaust gas flow past the turbine. It may overspool a little bit before the wastegate (?) comes in to let the excess pressure off. This is more revolutions and more stresses on your turbo. That's my theory and I don't want it to be right 😂.
my turbos have a 6" outlet that i have going to a resonator and then nothing. i know that using a turbo blanket helps hte turbo heat soak faster and provides faster 0-60 times. testing from the mfg showed as much as a 1.1 second drop in 0-60 with thick turbo blankets
Hi, Kyle! Not bad for an obsolete concept. But modern internal combustion engines expand to atmospheric, so all that fancy and inefficient goop becomes useless. Modern engines do gas transfers by positive displacement. If you'd like to see a modern engine design give me a shout.
My car is turbo charged. I just added a new after market axle back exhaust that has less back pressure than stock. I have noticed a reduction of initial acceleration within the city. Does that make sense? Why would this happen?
darotor go take a look at a mower or rc car exhaust. Its a common issue with 2 stroke engines so there is an expansion chamber along the exhaust somewhere. The exact size and positioning of this can alter how efficiently the exhaust is extracted feom the cylinder. Of course, 2 strokes dont have to worry about valves but the cylinder still behaves in a similar way. If you dont have an expansion chamber, just cutting the pipe to the correct length works too. (or positioning the first muffler)
On a 2 stroke scooter (back in the day :D) we usually mounted something like this: www.motorcycle-superstore.com/9610/i/athena-scooter-exhaust And it performed quite well. This weird shaped thing is apparently generating a backpressure "shockwave" to sorta seal the exhaust opening and prevent fresh air from coming down the exhaust, increasing the amount of air/fuel in the cylinder. Kinda different thing because.. well, it's a 2 stroke engine. I don't know the details anymore and I also don't know if that is actually working the way it's supposed to. It did increase peformance significantly though - in comparison with stock exhaust or no exhaust. Cheers.
Kyle i would like to know how to figure out what is the rpm or frequency the exhaust is tuned for. This would be helpful if i am picking a camshaft so i dont pick the wrong effective rev range. It would also help me to port the heads to know how much porting is useful in a engine because the exhaust is only going to help at a certain rpm. Knowing this we can build a engine that is optimized in exhaust, head flow porting, cams, valves, comp ratio, x pipe and intake. Speaking of intake, the length of the runners optimizes the engine powerband too can you do a video on why?
@KYLE.ENGINEERS: Maybe a little strange question but based on this explanation the backpressure before the muffler in a turbo diesel engine is lower than with a gasoline engine of similar performance?? For example: BMW X5 natural aspired V6 3.0 gasoline engine vs a 3.0d engine: Could I for example use the muffler of the diesel model and put it on the gasoline engine? Since from the power they are similar I assume the diesel muffler would perform as a performance muffler on the gasoline engine. Correct or completely false??
thanks so much. can you speak to supercharged cars? I've heard of and many that lost power across the range when they lowered back pressure by removing factory cats. all were tuned. it baffles me
The description is reasonably true for cross plane crank V8s but most other motors not really. Overlap is better described as intake/exhaust valve lead & lag. The inertia of gas flow from the intake charge is used to scavenge the exhaust. In one type of engine viz. cross plane V8, headers do actually work. In the real world (as opposed to a didactic concept) most other motors, so long as the exhaust is smooth (not even mandrel bends make much difference), then the I/E lead & lag determines the breathing ability rather than tuned length headers inducing scavenging. The gains that headers make in most other motors vs exhaust manifolds are from the reduction in pumping losses caused by restrictive exhaust manifolds. You see the problem in the real world is, that to get the correct scavenging effect it is almost impossible to for a motor operating over broad RPM to sustain the effect. The effect can and does occur but only in narrow ranges. This is fine for a race car but for a daily driver it 'ain't happening. On another matter there is a humorous video on denting headers and the effect on performance. It shows on an engine dyno what happens in the synthetic world: ua-cam.com/video/azPKIjxmmdU/v-deo.html
I'm still confused. Why used gas going back and hitting the exhaust vault when it's open DECREASE the pressure. And also wouldn't it just get more used gas into the chamber and mixed with the fresh air coming in????? Someone explain pls!!
Technically speaking, "Scavenging" is just the process of venting the exhaust from the cylinder and drawing in a fresh intake charge, what I talk about in this video is more Pressure wave or Harmonic Scavenging. There is also a bit to be said about gas velocity in the runners, but this video was already getting too long. Also, minor correction - at 3:30 I meant to say "combustion products" not "unburnt gasses"
Thanks for watching!
KYLE.DRIVES I look forward to every video you make, thank you so much for making these!
I love your content but the sound quality leaves a few things to be desired...
Excellent channel, I've just found and subscribed! Another very pedantic point, you say 'heat' when you mean 'temperature'. Yourself and many of your viewers will know the difference, but just thought I ought to mention.
***** thank you for that additional information. That really clears up the question of how less back pressure can become a problem.
C Sbastianygaumnitz it can smoothed out in a dyno tune. Or flap inside the exhaust you can control. I like to dyno exhaust changes. but who likes paying money each time you change Lol?
Whenever someone explains something in my field, I become very vigilant. And I have to say, you did a good job :)
4 years later and ur still helping people with this video, thanks man
I have watched countless videos about this subject trying to wrap my head around this concept and even theorized that a tuned exhaust could only benefit a certain rpm or multiples of that RPM/frequency just like notes in music complement each other others while other clash. Thank you for this video. It really helped bring it all together and and explain how back pressure plays a roll.
As a musician, that was the best explanation I could have read and it makes perfect sense to me.. so thankyou!
Great video. This is especially important on rotary engines. The main reason all pre renesis (RX8) engines gained huge amounts of power after putting a free flowing exhaust system on is because the factory exhaust system was the cause of excessive back pressure, once you put a larger free flowing exhaust system you saw anywhere from 20-30 % power increases. Unfortunately the renesis engine sees very little if any power increases (sometimes 5-10 kws if you are lucky) with an exhaust system upgrade because the side exhaust ports are the cause of the restriction in the exhaust.
Hey, I own a 99 GT Mustang. In 2013 I installed a pair of Flowmaster super 44 because of the " back pressure". Now, in January I installed a pair of Dynomax UltraFlo. That's a direct flow and, wow, the difference is huge. I can't talk about armonic or whatever, I can talk about the difference in power and response of that engine. Somenthing that I can feel.
even though I don't have much experience with Australian accents , I was able to understand you 100% . no muffles or "uhhhmmms" at all. Thanks!
You're mistaking back pressure for Flow Restriction, and the reverse pulse of exhaust gases into the intake is called reversion.
A flow restriction would cause a lower velocity in the exhaust gases which would result in a higher pressure would it not?
@@pizzaguy58 , without redoing the entire video, because this man's understanding of the terminology he's trying to speak of his inadequate for what he was trying to explain, I have to let you understand that a Flow Restriction it's not intentionally put into exhaust systems. It's usually an effect of an engineering anomaly. Exhaust Scavenging is done by tuning the exhaust so that adjacent cylinders are always drawing air and trying to keep the exhaust pressure as low as possible when the valves are in an overlap condition. Scavenging is best done by tuning the exhaust system so that the exhaust gases are at their lowest pressure in the manifold so that they don't cause a reversion up into the intake or as little as possible, when the valves are in a condition of overlap. At no time did I suggest that I Flow Restriction will not cause back pressure. But flow Restriction has not been intentionally designed in cars since the late seventies I think when they still had the heat risers on the right side manifold that would choke off the exhaust on the right side and force it underneath the carburetor to warm the engine up a little quicker. Some flow restrictions have been put into cars by accident or incidental misunderstanding of wave Dynamics. Any time an exhaust pipe is longer than 3 feet it starts to draw power from the engine because it starts to cause a problem with the way wave Dynamics occur inside a long straight piece of pipe. It is also why you have different size exhaust pipes built on to larger displacement engines because flow velocity has to be maintained in order to provide Scavenging to the individual cylinders. And there is no internal combustion engine that is perfect at that. The limitations of design require that there's going to be some pressure within the exhaust that is going to be higher then on the intake side of a cylinder because that's just the nature of the Beast. So I think you understand now the difference between Flow Restriction and exhaust back pressure fit is not necessarily designed into the engine but it doesn't affect of the fact that it can never be done completely away with. And I think the confusion comes in the fact that exhaust back pressure is piss poor terminology.
I see what you’re saying now, I misunderstood in the first comment. So then what would cause flow restrictions in a regular naturally aspirated exhaust? I thought you were referring to the restriction of flow through the sound muffling in the system. When I think of back pressure I think of anything that resists the flow, which I would think flow restrictions would be included in that. Am I wrong in that thinking?
@@pizzaguy58 only from a technical understanding. But it helps to be accurate so that you don't conflate your terms. This was not a good video for the explanation because the person doing the video was not aware of the proper terminology himself. At least not all of it.
I've seen reversion so pronounced that it actually creates a fog above the carburetor when you're racing on a dirt track or even an oval track.
This topic should be more discussed, would love to see more info from this guy about header diameter/lenght, different cone/spike shapes that close the headers end section and such
The laws of reversion
Look just tell me if I should do a muffler delete or not
If you got turbocharged car - make exhaust pipe going from turbo shortest possible. If supercharged or naturally aspirated, keep normal exhaust.
@@Fosgen i have twin turbo...... help
@@hawkeye7692 insta dump mate. straight outa the turbs dump that shit.
"Should I delete my muffler"
Answer: it depends.
Stop being cheap get a performance exuast system it will perform well
This is a much better channel than Engineering Explained. For starters, it's not bought and paid for by corporations
Excellent way to explain the concept at all, Im some one who knows nothing about engines, despite of this I have fully understand the concept, Awesome, thanks!.
So for turbo engines: open downpipe.
That’s exactly why I came here Lmaoo
I try it on mk4 1.8t and the torque was not as good as oem but it was epic anyway. 2.5'' downpipe it's better
@@s.lacasse8337 my mk1.5 MR2 has essentially an open 3" from the turbo back. Fantastic spool, great hp/tq, bit loud. Fabricating an exhaust right now that has a cutout that splits into a 3" extra quiet muffler and rejoins to a single exit. Silent mode -> race mode with the same 3" tip
Im sorry for being dumb but what is downpipe?
@@rohitdalvi9361 the pipe coming directly off the hot side of the turbo
You made a very informative video. What I learned is with an n/a motor, you should buy a well engineered exhaust system. And for a turbo car, just cut all the exhaust off or run as big as possible.
Yep, basically Ken Block's Hoonicorn
The least backpressure with the highest exhaust velocity produces the most power.
EXACTLY. That's literally how long the video needed to be. This "exhaust backpressure is good for performance" stuff needs to die a terrible, terrible death. 11 minute meandering explanations don't help that at all.
You explained things very well, however when you said engines will 'need backpressure' you should have rephrased it as a tuned system will result in some backpressure in the unoptimized area in the power band(which you sort of said). Otherwise well done and Ive been saying the same stuff for years and its nice to have a video I can link to save my breath lol
Excellent vocals - matters more than video portion. Wish American and Brit speakers could all do this well on youtube.
setting the overlap of the cam and cam timing is everything,but the exhaust design also adds to the scavenging,hence expansion chambers on race two strokes,some of the changes were dramatic to say the least,there are people in the industry that can give you what you want in design for your specific rpm range
Awesome video as always. Could you do a video on boost creep? Or refer me to anyone who has one
Added to the request list! Thanks for watching!
with 2.75-inch straight piping and a regular normal muffler I got a skyrocket rpm boost from 5k rpm to 7500rpm on my d15befi non vtec it feels wow at that rpm band point my experience helped me understand your explanation also good amount of torque is available at lower rpm also
There are quite a few points you have missed here, drag cars with cross plane cranks don't use venturi based scavenge effects like a flat plane cranks due to the different firing orders, the reason they don't use a collector mostly is because the scavenge is not really working in a V8 cross plane crank engine.
A flat plane crank like found in Ferrari engines for example can utilise a proper collector for exhaust scavenging effects, but these engines also have inherent vibrational issues as a trade off.
Pressure wave pulses work better from log manifold that that of collectors, but log does not scavenge using venturi vacuum and high velocity, scavenging using a venturi effect is better in a collector exhaust system and a higher exhaust velocity is essential to help even further, this is why a proper gauge exhaust tube is required for each engine to keep velocity high.
The turbo charging exhausts love a huge exhausts for your explained reasons. I had a twin turbo GTR a few years back making 500AWKW with twin 2863's on it and the amount of restriction in the exhaust housing was so great I had to use 33psi just to push against it. Also the twin turbo's run out of puff with LPM in the intake manifold compared to larger single turbo.
I should have gone with the larger single in the end to keep the LPM's up and use a lower boost pressure to achieve the same power.
Having such large boost intake pressures was not easy, the coolant temp levels were around 127C at some points around the 5th lap mark on track.
Obviously with pressure came heat and probably the most significant issue was the huge amount of pre turbine back pressure issue that would have been keeping exhaust gasses from escaping properly, I was well and truly pushing the limit of twin turbo's to levels I really shouldn't have been for the given power levels.
I could have cooled it more with better cooling systems, but at the end of the day, it was the poor little turbos that needed to swapped out for a larger, better flowing single.
Damn it had some crazy driving response though, it was an absolute weapon.
Good video Kyle, keep em coming mate, peace out from Perth.
Too long but interesting 😸
nice video! thanks!
it gave me some additional info about this subject. i was first misleaded by the title, because i couldn't believe that an 4stroke-engine really likes to see backpressure at the exhaust. but having watched your video, i understand what you wanted to point out.
When u have to much fancy words in ur head 7:12
Many....not much.
Hilarious
spam click 7.12 and it looks like he trying to record scratch LOL couldn't stop laughing
Thank you for the explanation... I had a torque box on my NA... I could run with turbo charged cars... My fozzies topend was amazing
Would love to see more detailed videos about engines :)
Good vid. Probably helped a lot of people. I would say that the content is pretty low complexity to moderate at best.
--A lot of people confuse what "Back pressure" is. There is no back pressure until the engine is running. Sound stupid, but basically back pressure is the result of engine dynamics. There is no reason for back pressure at all. Now, some people will call the pressure differential between exhaust port output and turbo exhaust intake as back pressure. I can see why, and whatever. But, beyond the turbo exhaust out, there is no reason for any back pressure. The only reason, to my understanding, why there is even an exhaust at all on a vehicle to to quiet it down and pass emission standards.
You just cleared up something i've been wondering about for quite some time. Think my diesel is ready for straight piping now :D
it'd be awesome if you could do a video just on n/a engines, (optimal intake pressure, temperature and resonance??) as well as more on exhaust pressures and design in race applications! I am looking to design a custom intake and exhaust system for an n/a engine (ej25 to be specific) to be used for racing, and am thinking of cooperating with bodywork for both the intake and exhaust. I'm wondering if designing an exhaust with similar properties used in diffusers (lower pressure at the exit) would effectively create a sucking effect on the exhaust? very interested to hear more about n/a!!
Thank you for the very informative talk. Can you address a few question I have about turbos in a future video? I want to know how much of the airflow the exhaust side of the turbine captures as it exits the engine. And what the turbine is doing when there is no effective boost. Or, does it always provide a small amount of boost?
I understand that when the vacuum reaches maximum on engine over-run, the fuel is cut, and only air is passing through the engine - using its compression to act as a brake - is that right?
What 's happening to the turbo on over-run? Does it stop, or just slow down? What would be the minimum sort of speed a turbo spins, with the engine simply idling?
When I get into the gas, but limit the boost to 0 psi, does that represent the maximum power the same engine without a turbo would make? (Or very close to it, due to the internal drag of a non-boosting turbo.)
What happens in the turbo housing when I get to peak turbo boost? Is the wastegate opening just enough to maintain the pressure on the outlet side of the turbo? I have a very small turbo on my old Tommy Kaira M20b, and I wonder what sort of revs it might hit at 10psi boost- would you hazard a guess? It makes some wicked sounds!
What happens to the revs of the turbine once the wastegate begins opening? Does it stay constant?
Just now finding this channel but this is a great question! (Or, rather, series of questions)
In all exhaust system, there is an expansion chamber in the form of a middle drum with no baffles, generally with 15 times cylinder sweep volume to allow the exhaust gas to expand sufficiently to maintain a stable anti-node and much reduced back pressure (near ambient) such that variation of pressure in the silencer system does not affect the header system much, this is more important for a tuned header, however, addition of a catalytic converter generally creates a significant back pressure while obviously being a stable node in the acoustic system of the header.
Air planes have tuned exhaust and zero expansions until the end of the pipe.
So i disagree that all systems have this middle drum.
Thinking of it the only expansion chambers I have seen are on 2 strokes.
Thanks for the video Kyle. This was a great explanation.
I have a 454 headers no cat convert flowmaster supper 44 not much back pressure runs just fine
you made it... thanks...
Thanks for this awesome explanation. Theres a lot of confusion with this topic
Outstanding.
I wish the term "backpressure" would die.
Invariably when people advise you "don't go too big or you'll lose backpressure", what they really mean is exhaust gas velocity.
As Bernoulli tells us, a fluid traveling at a higher speed is a lower pressure. Therefore by going to a smaller diameter exhaust, you are (increasing velocity and) actually losing pressure, which humorously is the opposite of what they claimed would happen.
MrClown indeed. usually when people go big, and thus the exhaust loses velocity it tends to bounce around and stack up and can result in increased BP. Proper built race cars run disturbingly small pipes and make killer power.
MrClown That's one aspect. Another is the reduced static pressure at the port due to the momentum of the previous exhaust stroke. It's easy to forget that for a while, the exhaust is flowing down a closed cavity, and this means that significant momentum in that flow can allow it to draw a low pressure zone in the pipe behind it, ready to aid the subsequent blow down event. This is the single most important factor when deciding which cylinders to connect in double or triple Y collectors.
There's a range of effective exhaust tubing diameter that will increase velocity, but not to the point of reducing efficiency of the system, i.e. going too small. In other words, there is an optimal size for a given system. Too small and too big create problems on either side. Flow dynamics are an interesting science.
I remember the last time a had a icy smoothie the bigger the straw the bigger gulps I had and the easier it was to get it out, but in a small straw fucking turned into a sucking workout!
Lifted_Above and how do we analyze that? Cfd?
dig the channel dude. Quick question what's your opinion on why drag car zoomies (straight out pipe no collector) don't have a bell mouth or trumpet funnel arrangement on the discharge.
Ps to anyone else reading, don't skip the adds and click the add links and likes so this bloke can get something back for the effort he's putting in. I bet he paid a lot for his engineering lessons i'm happy to pay 20 seconds for mine.
It is not an anti node rarefaction of a standing wave, it is an expansion wave that is reflected from an initial compression wave that is created by the sonic (speed of sound) gas flows just as the valve or port opens which rapidly drops to sub sonic flows in the exhaust, while the compression wave continues at the local sonic velocity of the gas in addition to the velocity of the gas, when compression wave meets an increase in pipe area (outlet or collector inlet) of any kind it reflects a mirror copy of itself as an opposite pressure signed expansion wave that travels back up the exhaust pipe at the local sonic velocity minus the forward gas velocity.
The expansion wave is timed to return during valve overlap, that is determined by the length of the pipe from the valve to an increase in area which is the distance the wave will travel and negative wave will return know as "tuned length".
If the time the waves take to traverse that distance in the pipe, determined by local sonic velocity (speed of sound) in a gas, is the same amount of time as the exhaust open to inlet open occurs at a given RPM, then the expansion wave will draw more intake in then would be the case by mere pumping.
I have a bunch of videos on the topic mostly 2 stroke and one recently on inertial scavenging and how it compensates pumping losses of the piston rising after BDC in a 4 stroke.
AuMechanic I've seen moto3 bike with single cylinder with dual exhaust (one outlet per valve design), does this amplify the return wave strength thus increasing engine volumetric efficiency at a specific rpm range?
@@soraaoixxthebluesky Yes it probably does, also keep in mind that the tapered cone shape at the end of the exhaust pipe (called a megaphone) has the function of making the reflected expansion wave effective over a wider RPM range than a straight pipe outlet is limited to, something this video failed to mention, a note a properly designed 4 into 1 exhaust will also have a taper section after the collector for the same reason.
Liked it ! When i took my catalitic converter out, it actually made it worse....started to loose power at high rpm, and the top speed dropped....also the mid rpm torque dropped.....
You need long tube headers you basically moved your back pressure to your muffler, either get some bends in the exhaust or get some longtubes
That's why for a N/A engine you need "Tuned Length headers" for your displacement/cam timing. Shorty header only save weight and give no/very little power on a current OHV V8.
Also why NHRA Pro stock cost so Much.....I've seen than they can actually get better VE ?supercharging effect than Old 90's F1 cars.
Greatly explained, definitely better than EE.
Great video.
You're somewhat close with the resonant tuning, but you're missing a major point.
The cylinder still has a bit over 100psi in it when the valve is opened. This is... massive... compared to any other pulse tuning pressure in the car. The result is that about half the residual gas leaves the cylinder before the piston has moved up any significant amount. The ideal negative pulse arrival time (at the valve) is top dead centre. If tuned correctly you can end up with negative 4psi (gauge) in the cylinder when the intake valve opens. This is why overlap is so important on a race car, and why cam specs influence header design. The major effect is on the same cycle, not the next
Look at this graph
musclecardiy.com/wp-content/uploads/2015/01/8.jpg and note that peak vacuum occurs fractionally before tdc.
and download the "engine analyzer" demo from performance trends to see the effect and data of tuning exhausts. Try a 40" primary pipe on the demo engine and see what happens when you get the full action of the 1st reversion pulse
Thanks for the insight. I'm going to look into this topic more. Understanding air flow and pressure gets me excited.
hey mate you seem to know a lot about what your talking about it would be great if I can ask you a couple of questions
@@jamier9113 go for it. Can't promise much though
Skippy cheers I appreciate it I have a 4litre 1grfe petrol engine and I have just bought and on Friday will be installing long tube genie headers and removing 2 out of the 4 cats with a stock ecu is it still possible to get good Benefits and is it possible for scavenging to still happen?
@@jamier9113 I just had a look at that. I'm assuming you have a hilux. They have pretty poor manifolds that look like a pipe bolted to the head, so literally anything is an improvement. Half of manifold design is eliminating screwups. Genie looks like they eliminated the biggest screwup of having mitred joins. Incidentally so did Toyota with other apparently interchangeable headers.
By removing the cat converters you have also improved flow.
Between those two things (having real bends and having less cat converter to deal with) there will be significantly less residual pressure in the exhaust ports, so you'll have a much better situation at overlap. You'll probably gain, I'm gonna guess, 5% under any given condition. This is basically avoiding screwups.
As for real scavenging (making something genuinely good) I don't think it's going to work. They aren't long enough to get the acoustic tuning right. They are also probably too large for inertial tuning (which to a degree sucks the exhaust out once the above mentioned blowdown pulse gets things moving).The Genie headers are 44mm in diameter, ideal size for a 500cc cylinder at 4000-ish rpm is 28mm. I don't feel like doing the maths on the 1GR but I'd be surprised if they were supposed to be bigger than 35mm.
I don't think for a second you've made a bad choice, there's every chance the Toyota exhaust port is too big to put a good header on it and there's probably not enough overlap to make the most of it even if you did
very informative video🙂
i actually learned something this time...
hey man, great video. can you do a video on the effects of having a vacuum in your crankcase (how/ if it helps with piston ring sealing and how/ if it helps with lubrication). Thanks a lot
Within tuned range, I don't agree that coupled exhaust will create sucking effect for next cylinder., at least not in time. Instead , it will have positive pressure when next cylinder starts opening exhaust valve, and travel to other cylinder. This positive pressure will reduce overall VE of the engine. Because it is able to cancel or reduce negative return pressure. However, it is depended on length, angle , diameter of the primary runners.
Maybe this is the reason why drag car use individual exhaust runners.
shao jom drag cars and recing cars just focus on specific rpm band. Therefore they can design diameter and length just nice for that rpm.
Normal everyday car needs to cater from low until high rpm (if possible)
Therefore, scavenging helps in these low rpm region.
However, I have not gauge any exhaust with a pressure meter.
That would clear any myths.
It's not so much the wave speed within the exhaust but exhuast valve opening events. As the engine rpm (frequency) increases, the exhaust valve opening time (in seconds) decreases. With a fixed mean path length of the exhaust being fixed the opening events and the density wave go out of phase.
Good video however I strongly disagree with a comment you made a few times about scavenging not really being important or an issue for a turbo engine.
Any opportunity allow a turbo engine to operate closer to an n/a engine should be capitalized on.
Removing pre turbo emap allows you the potential to improve VE.
As you know, Fluid dynamics dictate that fluid will flow from the higher pressure point to the lower. Creating a window for the engine to operate in where inlet to pre turbo exh pressure is under a 1:1 ratio, allows scavenging to take place if valve timing, fueling and ignition is optimized.
This will absolutely help with turbo spool, off boost torque and drive ability, engine efficiency etc.
Scavenging can and does work on turbo engines too.
can you use the two stroke engine exhaust effect to scavenge the cilinders
Well explained
Thanks for the great video, I put a gasket on the connection between the muffler and the exhaust pipe for a better sound. It can be said that this part of the exhaust is leaking now, will it damage the car engine in the long run or not?
Gasses have velocity and inertia. Pulse scavenging is more for two strokes. A smaller pipe will have higher velocity and inertia. Bigger will be lower but less backpressure but less inertia for scavenging on the overlap. Differences will have more or less power at different rpms. Now many motors have valve flaps down pipe in the exhaust to tune the inertia for all the rpm range.
I ran my exhaust on my 1995 S Series with a 1991-1992 GM factory header, a pace setter high flow cat converter and a factory muffler and the same size pipe. I also have a ported intake manifold , bigger throttle body a cold air intake, and totally upgraded suspension and a polyurethane master bushing kit, and although I'm gonna build it .20 over for a Turbo setup and dual intake cams, etc It has the perfect amount of torque, at the moment , back pressure for what it is. I don't have to even give it more than a third of a petal cruising and I look down at speedo, and I'm at 70-75 MPH in no time. But the car is only 2280 LBS with ample torque...lol It's gonna be downright nasty with 320-350 HP and RPF1 Einkei 15X7's and 205 50R 15 Toyo Proxies in the coming months...lol
At the end u do a muffler delete in turbo cars and all is well but only after u increase the boost otherwise leave it alone..my audi went fro 7 psi to 14 psi so I cut it off ..no problems..smooth
I am work in a vehicle workshop, this video is very helpful for me.
Can I ask a question? we know at some car, there is a exhaust flap that close at low RPM to increase torque, and open at high RPM for reduced exhaust resistance.
But how the torque increased by close exhaust flap?
I've just seen a video in which a fellow youtuber explained that in engines with 4 cylinders or more, exhaust pulses start to overlap, causing vortexes that decrease the efficiency of a turbo. Maybe you could make a video on that subject and go into a bit more detail ;-)
Keep up the good work, mate! :-)
so a muffler delete would make a car lose HP? because of back pressure?
You are confusing the hell out of people by calling transient waves "back pressure" they are NOT, the overall actual back pressure does not change because of them. Also 5:20 you say a negative pressure should get to the exhaust port at valve opening. NOT so. The flow out the exhaust valve at that time is *choked* and no amount of suction down stream can affect that flow at all. The negative wave is timed to arrive at the exhaust at it's *closing* time and during overlap where it can pull out remaining exhaust and start pulling in fresh air from the intake. You are supposed to know this stuff.
I definitely learned a thing or two regarding turbo exhaust... keyword “free energy” dump pipe.... for the win.🇦🇺🤜🏼🤛🏼😂🍀😎🎅🏻
I once came up with this idea about a sliding pipe system which would always keep the harmonic scavenging right at the rpm you are at
That's alot of moving parts
Simply put, it is an input/output system. Efficiency (power) is the greatest when the system is in balance. Pull the exhaust off a stock engine and it will run terrible. You could retune to compensate but the engine will run rather inefficient outside of constant high rpm.
Great video, now i know where the extra power coming from
Lower pressure in the exhaust after the turbo help response does it of it spooling up
Obviously you aren't a drag racing guy, but if you could, I'd love for you to expand on the pros and cons of zoomies (isolated primaries) over collected headers. I've seen a few guys, when horsepower isn't an issue (as in tire limited classes where they have all the power they need but just have to figure out how to get it to the ground) prefer collected headers because they are "easier to tune". Im assuming its due to only requiring one o2 sensor per bank (therefore simplifying the data) as opposed to an o2 sensor per cylinder, but I'd love to know if I'm oversimplifying it, if I'm completely wrong, or if I'm on the right track but missing other variables.
I understand this isn't your arena, but I'd appreciate the engineering/fluid dynamics view I think you may be able to provide.
Thank you brother
Excellent video Kyle!
Thanks for clearing up the myth about engines needing back pressure for so many uninformed folks.
An ICE is basically an air pump. A working understanding of hydraulic circuit theory would quickly clear up the whole back pressure myth.
great videos , this deserves more views
Hi have a question.
I am making my car repaired and probably made some mistakes in exhaust system. Car is Jag x type v6 and both catalytics are broken - one emptied other is probably clogged. Car idles say for 3 mins then engine dies. Exhaust guy suggested me to place a universal catalytic where pipes from cats unite so there is now one catalytic on line before exhaust mufflers.
After spark plugs replacement i can drive car for say 5 minutes then engine dies on the move, wait 10 minutes then car runs for another 5 minutes.
So i think a big back pressure builds up and engine dies because there was not this issue before installing universal cat.
I plan to remove new cat and let exhaust float easier until i find good cats.
Thanks in advance. Cheers.
Hi Kyle.engineers, thank you for explaining the flow in the exhaust. I found this verry interesting.
I stumbled upon you’re video as I was looking for a faultcode on my MB C class 180D 2015 model.
The car has a fault code on the exhaust back pressure sensor (P047121A). I will replace the sensor, but what is actually the function of this sensor? Does this has anything to do with valve timing to reduce the backpressure (as this is a turbo charged car)?
The fault comes up after overhauling the DPF (almost immediately) and I was wondering, why is this at this moment, what is the logic of that.
this guy makes some great content
Interesting that a recent episode of Engine Masters showed that back pressure is undesirable for best performance and that the "smaller exhaust enhances torgue" idea is a myth. Dynamometer results were confirmation of free-flowing exhaust enhanced horsepower and torque both. Anti-reversion in both intake and exhaust were more effective. When I port and gasket-match intake and heads, I leave a. 030 anti-reversion "lip" on the intake port of the manifold and one on the exhaust port of the cylinder head. Power is enhanced as well as scavenging. My header design is optimized for 2,000- 3,500 rpm for daily drivers with different designs for performance engines based on the appropriate rev range. The port "lip" remains the same regardless. Between catalytic converter and muffler restrictions, there is plenty of backpressure. Post turbo scavenging is the same as you illustrate.
so in otherwords, increasing exhaust diameter will "shift" the power band up in the revs and decreasing it will give better low end? and in both cases straight pipe/laminar flow mufflers is the way to go; correct?
mas921 not necessarily, especially when the pulses is not interconnected, therefore no scavenging.
And, when no scavenging, no harmonic scavenging aka 'supercharging effect'
In other words, it have to be 'just nice', with your engine configuration, setup and tune.
Just at the nice rpm that you targeted for.
Am I watching Engineering Explained? lol
Nope, EE at least explains things better and can draw more clearly.
Knight Fox The. I sub from this Chanel and go watch your EE. This guy does an excellent job at explaining and he dosent have newtlybthe time to practice as long as EE has been doing this.
I find EE to be better aimed at the novice viewer where Kyle explains better to those who already have some knowledge. EE also shows more math, but it's easy to gloss over that math if you don't understand what he's doing.
Both have their pros and cons. It's good to watch both
Kyle explained more advanced concepts
This is called supercharging effect on intake and exhaust besides only siphoning and scavenging.
Right Kyle?
That's why complicated fluid designers and engineers went to variable length, variable route, and variable pressure restrictior to maximize the 'supercharging effect' of the intake and exhaust pulse, for as wider rpm bandwidth as possible
Where is the EGR valve in your drawing? The EGR takes exhaust gases and runs it through the engine again. Does that affect the back pressure? What happens to the exhaust with crossover pipes?
What would happen if there is a "back pressure " of only 800 /500 millibar or assume we have a wall and it it empties into a vacuum of several thousand m3(never have any back pressure ,always "sucking "out) ?
You could have added the factor of compression ratio or compression inside cylinder. Usually, the engines with EGR systems and no exhaust gas coolers have a lower compression ratio. In these cases, what would be the effect of reducing your exhaust backpressure?
Simple way: No back pressure = most power
So straight pipe lol
Probably jumping the gun here at one third through the video, but there can’t be enough said for the effects of valve seats.
It’s that split second as the seal is broken that creates crazy fast air speeds due to pressure differences.
Trick multi (3+)angle cut valve seats are a real world upgrade.
🇦🇺🤜🏼🤛🏼🎅🏻🍀🍀🍀😎🤓
So the turbocompressors are the only places from where the engine gets air?
I’ve removed my catalytic converter on my turbo diesel truck and the engine runs smoother but I have lost some of the initial torque. It kicks in much later now..what can I do to get torque to kick in at a lower rpm
You should talk about turbos that are mounted in the rear muffler. It spouse to be working better. Or is it?
Great job on the explanation.
So does the increased work that the turbo does reduce its potential reliability? E.g if I take my muffler off will I blow my turbo?
Since you are not altering the characteristics on the side that needs pressure/pulse waves for combustion chamber efficiency simply put, deleting the muffler (even the catalytic converter as well) on a turbo setup is generally BETTER for the system. Disclaimer - I AM NOT AN ENGINEER! This is what I've noticed from personal experience, a slightly educated guess at best so consult a professional lol.
This seems to be the consensus however my gut says if you free up one side of the turbine then your turbo can spool faster as there are less restrictions on exhaust gas flow past the turbine. It may overspool a little bit before the wastegate (?) comes in to let the excess pressure off. This is more revolutions and more stresses on your turbo. That's my theory and I don't want it to be right 😂.
my turbos have a 6" outlet that i have going to a resonator and then nothing. i know that using a turbo blanket helps hte turbo heat soak faster and provides faster 0-60 times. testing from the mfg showed as much as a 1.1 second drop in 0-60 with thick turbo blankets
It's like if the host of 'Engineering Explained' had actual engineering experience.
yeah, didn't he start his channel pretty much while in the end of his schooling?
is this what they mean when people say that an engine has a power band, having a certain rpm range where they are really strong?
This video was really informative! Thank you!
Hi, Kyle! Not bad for an obsolete concept. But modern internal combustion engines expand to atmospheric, so all that fancy and inefficient goop becomes useless. Modern engines do gas transfers by positive displacement. If you'd like to see a modern engine design give me a shout.
thanks for the video, 5 points for Gryffindor
I wish I could like this video twice.
If I decrease pipe diameter in my system is that going to increase back pressure?
is catless downpipe+straight pipe good for a turbo diesel engine
My car is turbo charged. I just added a new after market axle back exhaust that has less back pressure than stock. I have noticed a reduction of initial acceleration within the city. Does that make sense? Why would this happen?
In a NA single cylinder, where is the rarefaction developed from if there is not throat collector in the exhaust?
darotor go take a look at a mower or rc car exhaust. Its a common issue with 2 stroke engines so there is an expansion chamber along the exhaust somewhere. The exact size and positioning of this can alter how efficiently the exhaust is extracted feom the cylinder. Of course, 2 strokes dont have to worry about valves but the cylinder still behaves in a similar way. If you dont have an expansion chamber, just cutting the pipe to the correct length works too. (or positioning the first muffler)
Don't forget things like powerbombs on 4 stroke, single cylinder dirtbikes! www.motorcycle-superstore.com/6492/i/fmf-powerbomb-stainless-steel-header
On a 2 stroke scooter (back in the day :D) we usually mounted something like this:
www.motorcycle-superstore.com/9610/i/athena-scooter-exhaust
And it performed quite well. This weird shaped thing is apparently generating a backpressure "shockwave" to sorta seal the exhaust opening and prevent fresh air from coming down the exhaust, increasing the amount of air/fuel in the cylinder. Kinda different thing because.. well, it's a 2 stroke engine. I don't know the details anymore and I also don't know if that is actually working the way it's supposed to. It did increase peformance significantly though - in comparison with stock exhaust or no exhaust. Cheers.
would not some pressure in the exhaust reduce or eliminate "jerk" when the piston is going up and then instantly reversing direction?
With turbos the pressure for turbine is for large portion the result of heat due to gas expansion.
Kyle i would like to know how to figure out what is the rpm or frequency the exhaust is tuned for. This would be helpful if i am picking a camshaft so i dont pick the wrong effective rev range. It would also help me to port the heads to know how much porting is useful in a engine because the exhaust is only going to help at a certain rpm. Knowing this we can build a engine that is optimized in exhaust, head flow porting, cams, valves, comp ratio, x pipe and intake. Speaking of intake, the length of the runners optimizes the engine powerband too can you do a video on why?
@KYLE.ENGINEERS: Maybe a little strange question but based on this explanation the backpressure before the muffler in a turbo diesel engine is lower than with a gasoline engine of similar performance?? For example: BMW X5 natural aspired V6 3.0 gasoline engine vs a 3.0d engine: Could I for example use the muffler of the diesel model and put it on the gasoline engine? Since from the power they are similar I assume the diesel muffler would perform as a performance muffler on the gasoline engine. Correct or completely false??
thanks so much. can you speak to supercharged cars? I've heard of and many that lost power across the range when they lowered back pressure by removing factory cats. all were tuned. it baffles me
The description is reasonably true for cross plane crank V8s but most other motors not really.
Overlap is better described as intake/exhaust valve lead & lag. The inertia of gas flow from the intake charge is used to scavenge the exhaust. In one type of engine viz. cross plane V8, headers do actually work.
In the real world (as opposed to a didactic concept) most other motors, so long as the exhaust is smooth (not even mandrel bends make much difference), then the I/E lead & lag determines the breathing ability rather than tuned length headers inducing scavenging.
The gains that headers make in most other motors vs exhaust manifolds are from the reduction in pumping losses caused by restrictive exhaust manifolds.
You see the problem in the real world is, that to get the correct scavenging effect it is almost impossible to for a motor operating over broad RPM to sustain the effect. The effect can and does occur but only in narrow ranges. This is fine for a race car but for a daily driver it 'ain't happening.
On another matter there is a humorous video on denting headers and the effect on performance. It shows on an engine dyno what happens in the synthetic world:
ua-cam.com/video/azPKIjxmmdU/v-deo.html
I'm still confused. Why used gas going back and hitting the exhaust vault when it's open DECREASE the pressure. And also wouldn't it just get more used gas into the chamber and mixed with the fresh air coming in????? Someone explain pls!!