What Does A Bull Horn Exhaust Do??
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- Опубліковано 6 лис 2023
- Help me understand what is going on in the comments please! The exhaust pressure HAS to be doing something...
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My thoughts - the scales are intended for a "static" weight (i.e. not moving). They probably have some sort of analog or digital smoothing built-in, with a certain time-constant. Once you introduce movement (engine vibration) the movement could be interacting with the smoothing algorithm producing a false reading. Google "signal aliasing". Due to different scales having different types and responses of filtering, one would expect two different scales to produce different readings. I do industrial PLC controls, and have observed the phenomenon before (not with a race car though...). Readings that make no sense would suggest this or a similar situation. Cheers from Dan In Phoenix!
I did see what appeared to be rotational torque twisting the front wheel weight in one of the pulls , and vibration is likely one factor influencing the scales
I was thinking the same thing.
Pretty much what I'm thinking as the baud rate of the digital scale is taking an average of the changes. The thrust will be virtually immeasurable in any case when flowing through a five inch hole without full load.
Nah the scales work just fine. Car needs to be on dyno and under full power. The downforce you’re getting is from thrust, it’s works very differently than static weight. Need a lot of exhaust gasses escaping the bullhorn.
I’ve seen over 200 lbs from my own car and it’s only a small v6 with twins.
@@5uprnva Hmm... Questions: If the scales are fine, then you should be able to use any scale and get the same results. Steve used two different scales and got two different results. Also, the pipes are directing the exhaust up, which should result in downforce (heavier), but the first scale recorded the opposite (lighter) and the second scale recorded essentially zero change. I'm having trouble understanding how the scales (at least both of them) can be fine. For your own reading, how did you measure it? Just curious. For a chassis dyno, when the car is under full power, the rear wheels are spinning (can't put scales there) and the front wheels are trying to wheelie from the rear-wheel torque, so scales placed under the front wheels would give a meaningless reading.
It would be interesting to see you place a steel plate/ heat shield on top of one of the scales and face the exhaust downward onto them and see if it measures exhaust force that way ?
That’s what I was thinking, turn the pipes down place scales under exhaust and waste gates , end of the day, what little exhaust thrust pressure there is, what about any aero lift this car has as it goes down the track , are there shock travel sensors fitted? Why not see logs of pipes down, then backwards and then upwards and see what the shock data shows
It should be down on a scale as mentioned but while on a dyno under full boost.
it's not going to have enough force to read on a scale, or at least not a scale that is calibrated for car weights. The best way I can figure is using something like a linear strain gauge with something like a parachute above the exhaust to measure how much force is being put out
I’m bad at math but, if you have a given exhaust size and could put a ball of given weight into a tube of same diameter I would think you could figure flow and maybe velocity
There is not very much pressure in the horns that are open like that and they are pushing against air, not something solid. You would need a scale that measures in tenths of an ounce to get the measurement of the amount of actual downforce the exert on the car.
I think the simplest way is to do an A to B comparison. Put it on the hub dyno with scales. Run a pull with the exhaust straight back. See how light the front end gets. Then run them at a 45 degree angle. Same tune. See how light. Then point them straight up and run the same pull again. Try to keep as many variables the same and then see how much weight difference there is in lift.
Steve, I think you should put it on the hub dyno for this test. Put the scales under the front tires and let it rev up and pull instead of just breaking up at a steady rpm. I believe this is what you need to simulate a run. You will have strapped down weights and weights on a pull, also can test the difference in direction they point. Great content again as usual! Thank you. Brian
I didn’t think about the hub dyno, but my thoughts were if it’s on the two-step then it’s not a steady flow of air it’s intermediate unlike after letting up the button and going down the track, or in this case on the Dyno
If you want force from expanding gas you need to look at rocket engine cones. If straight pipes worked well then nasa would be using them.
Surely you understand that an engine rocketing down the track at boost is producing exponentially more volume of exhaust gas (and therefore more thrust) than an unloaded engine revving with little to no resistance. You said 1200 hp from 540 ci at 8 lbs boost. Loaded, yes. Unloaded, hell no. Factor your fuel consumption on the dyno under load vs just revving it in neutral.
Imagine a car traveling on a level road overcoming nothing but wind and rolling resistance. It takes 6 hp to maintain 60 mph. Add a 4000 lb trailer, 5 adult passengers, and their luggage. Fuel consumption will at least double, as will the volume (and pressure) of the exhaust gas, even though the same engine has the same rpm.
Unless I'm completely misunderstanding your conundrum.
@@billharbers3409have to agree this makes a lot of sense to me
For the dyno to work, it has to present a load. Torque applied, equal and opposite reaction, nose is going to lift and take weight off the scales anyway. Maybe an a/b comparison with and without the pipes would do?
Steve! Awesome video and the weight loss is due to an unbalanced equation. Your waste gate comes off the high pressure side of the turbo across a small surface area (the pipe) while pointing down creating lift. Your exhaust comes off the low pressure side of the turbo with a large surface are reducing the thrust. The lift from your waste gate is overcoming the down pressure of the exhaust.
Close your waste gate (like on a launch) and you’ll see a huge spike in front end weight. I can help with the trust calculations later tonight.
Sorry for the delay in calculations! These are rough numbers; if I'm wrong, please correct me (politely)!
Thurst a force. Forces are measured by changes in force over time. This thrust equation will be the mass flow rate/time OR the exhaust density x engine capacity x revolutions / s x speed of the exhaust. I will calculate in metric and then convert them at the end
Air density at 8lb of boost = 1.32 KG / m^3
6.5:1 air-fuel ratio for methanol weight = .20 KG/m^3
Exhaust Density = 1.32 + .20 = 1.52 KG/m^3
540 CI to M^3 = .0088m^3
5400 rpm to rev / second = 90rps
Exhaust speed (Chat GPT Provided) = 400m/s
1.52*.0088*90*400 = 481 Newton OR 108 pounds of thrust (downforce assuming the bull horns are pointed straight up)
There are many assumptions here but this will significantly increase as the boost numbers increase after the launch.
Steve, I love the channel! I've been racing with my family since I was 8 and run a SBC 1978 Camaro out of Norwalk Ohio that runs mid 9's in the quarter. Keep up the good work!
I think you did some great work here, but I would like to politely share my calcs to compare. Considering it takes 2 revolutions to get 1 exhaust stroke, you should only get 0.0088/2 * 90 rps. This comes out to 0.396 m^3/s of exhaust. This is split to two 5” exhaust pipes. Each pipe should have 0.396 m^3/s *0.5 = 0.198 m^3/s of volumetric flow rate out of each pipe. With the cross sectional area of the pipe to be roughly 0.01267 m^2 we can calculate a velocity of 15.627 m/s.
Thrust Calc: pA(v^2)
My calcs only come out to 4.703 N or 1.06 lbs of force at each pipe making a total of 2.12lbs of force.
Considering the thrust provided is a function of velocity squared, the large diameter of the pipes just don’t provide the velocity (at the conditions provided, if my calcs are correct) to make much impact.
Please feel free to correct me if I’m mistaken (politely) lol
@@stephenkeighley7993 I feel like this is closer to reality, if you had 480N (around 40kg, or 20kg each exhaust) acting on the exhaust tip, that would have an equal and opposite force applied to the pipe itself, judging by the video it might also move the pipe due to no visible supports at the end of the pipe
For test purpose flip bullhorns down and see how much weight comes off the scales
That will work - force against a stationary object...not air.
Ya this is logical. The exhaust pressure will have a fixed force to push on (the ground). The atmospheric pressure (1 bar) is not great enough to generate any downforce (my opinion of course).
But it will be pointless data. He needs the difference between exhaust pointing back vs up.
@@AB-80X yes but will at least prove his point possibly
Looking to establish the variable
There are too many turns in headers for the air flow to register discernable downforce because of the equal and opposite forces being enacted within the head and header tube turns after exiting the combustion chamber. It's basically like pointing a box fan at a sail on a boat, the sail and the fan thrust cancel out as long as the box fan and sail are both attached to the same structure. Hope this makes sense. There will be SOME downforce, but not nearly the full weight and power of what you expect because the internal air forces against the ID of the header tubes are causing that equal and opposite counter-action. source: fighter pilot with engineering background.
I believe the bull horns ARE adding down force but unless you compare it to the old setup you're not going to see a net gain. Torque is always going to lift the front end to some degree, so the test needs to be a measurement of how much less it's lifted. If the front end looses 100 lbs with the old setup and only looses 50 lbs with the horns turned up then you're effectively adding weight to the front end.
torque will only lift the front end if the back tires actually rotate, with them beeing stationary there is no torque that could lift the front up. the only torque happening is the twist of the engine itself
and as the power comes on the front wheel will lift and come of the scale - you would need a force gauge between a fixed point and the hood or top of the axle stub to measure the net force during the torque rotation period @@SharkyMoto
Steve
Looking at the scales the bit extra revs increased your weight by 10 Lbs
Remember you have enormous exhausts and at low revs the volume of air going through there is minimal
As you start to build boost and revs, the motor pumps hot air at higher temperatures and volumes, it will start to make a huge difference because the exhaust will be running full.
Like a garden hose pipe. If you have it on at 1/4 it makes almost no opposite reaction because there is no friction in the pipe because it is running free. When you crack it wide open and the water is being forced out there under pressure it is significant in its reaction.
Remembering p=v*a you can quickly see the a (area) remains static but BOTH you pressure (p) and velocity (v) are INCREASING SIMULTANEOUSLY and that will make a significant difference. So, as you build boost and engine revs, the dynamics shift together because you are not changing one parameter but TWO, SIMULTANEOUSLY
Hope it makes sense
Maths and physics and stuff 🤔
Steve, your turbos pull air from above and down. You effectively are lifting the car with your turbos. Connect a makeshift tube to aim the turbo air inlet direction forwards or sideways, just for temporary testing purposes, and you should see you create some down force then.
You beat me to it. Exactly what it was thinking.
Said the same thing, I didn’t scroll down enough. Every force creates an equal and opposite reaction.
Yep Newton's Third law. Can't beat Physics! You beat me as well!! And Steve for top fuel you are correct but there is over a 10,000 HP difference. Let's say the air pump is moving a lot more air.
But would that overcome combustion pressure, exiting from the exhaust in an upward direction. Essentially, you’re adding energy to the exhaust greater than the turbos create in taking air, through the combustion process.
@@MrNofuns2 Oxygen is depleted during combustion therefore there is less volume going out than coming in. Think of the size of the valves.
Engine displacement times the RPM, then halved gives you a per minute volume. With your specs your making about 41,230.8 per minute of air volume. time 60 then divide by 1000 gives you 2,472.6 per m3/hr. I put that in a air flow conversion calc and it gave me 30.3miles per/hr of air flow out of a 5 inch pipe. 1 lbs of thrust is equal to about 21 mph wind speed. idk what size is the wastegate pipe but im guessing around 2.75 inches. having said that the wastegate pipe is putting out about 100.2 mph of wind force. which is about 5lbs of thrust. Mind you this is only with the 8 psi of boost so should be way more on wastegate closes and all 50 psi of boost is available. Theoretically at full boost you should be moving 1,404.5 mph of exhaust flow which is about 66lbs of thrust per side so 132lbs all together
Good Evening Steve, I loved the video.. as an engiener i wanted to do some numbers.. i worked out the force should be approx 22Lbs, based on twin 5 inch pipes. seems to allign with the weight changes of the scales in the video. Remembering becuse the car is turbo you are extracting a lot of energy from the exhaust gas so youll be at a big dissadvantage comapred to a top fuel car running zoomies.
Seems the easiest way to test would be to put it on the chassis dyno, then test it with the bull horns pointing up and then down. Toque reaction will make the front end get lighter no matter what, but if you do a back to back you can isolate the exhaust thrust.
Exactly
Ha great minds think alike👍
That's what I thought too...
I like the way u think.
I was thinking the exact same thing!
You need to do the test on the hub dyno with the scales under front tires and also a tape measure to see the difference in the rise on the front end with both scenarios
TORQUE . . .. makes it irrelevant. . . Cletus will tell you good oll horse torques or bald eagles. . 🤣
@@maineturbodiesel780 it will actually show if the horns produce even thrust to push the car down
Hahaha the dyno torque would lift the front end rendering the measurements useless, only way is to put something directly above the exhaust and measure it like that.
@idgaf5252 which would show real world, not fake numbers 😉
After Steve jumps in the car the scale: ERROR !!!!! OVERLOAD!!! 😂😂😂😂
My thinking is that by the time the exhaust gets to the bullhorn, the hot side of the turbo has already extracted a whole lot of energy from it to compress the intake charge. What remains isn't enough to produce thrust.
Fully agreed
it produces thrust but not as much :)
It's all about mass flow and since your intake is also vertical they are canceling each other out and the wastegate flow is the difference.
Basically the turbo inlet is sucking as hard as the turbine is blowing (with some expansion that should make the exhaust push down harder than the intake sucks up) but the gates are the equalizer
exactly
Should bring the waste gate exhaust out and point it up also
Once car is moving the aero flow will change whatever is measured standing still. Intake tubes for example looks to be in a high pressure area.
Bingo
@@wajfaj yes but if they weren’t there the high pressure would also be pushing the wheels down. Basically this is a jet engine bent in a horseshoe
There are some really good theories in this thread. The leaf blower analogy works well in my mind. They're always rated in "MPH" or "CFM" never "PSI". They can move a whole bunch of leaves in a hurry, which is a lot of work being done, and a lot of flow, but they can't lift much more than a basketball, which would be PSI. As someone else said, that's why you want a 5" exhaust on an engine that powerful; lots of flow and low pressure. Cool experiment!
Leaf blowers still create thrust though. This can be tested by powering carts in physics class. Lots of leaf blower powered vehicles on UA-cam
@@erichamm4628I agree. Pressure is not relevant for thrust as some people already explained.
If you can lift a basketball with a normal leafblower, imagine what you could do with a 4500hp leafblower
“We are learning that we don’t know what’s goin on” yet sounds deadass accurate. That’s when you know your nipping it in the bud!! 💪🏻💪🏻
Thrust from things like jet engines involves bringing in cold air on one side, and compressing and heating it, then forming the exhaust side with a nozzle. Steve's cold air intakes are pointing upwards and so are the exhaust. Those pointing the same direction instead of opposite direction cancels out quite a bit. The air has mass and it's moving the same amount of air down (on the intake) as it is moving up (on the exhaust). If the intakes faced downward or forward it would be different. The scales are also probably averaging and not giving a very good reading. Conservation of energy also means there's a torque being applied to the car due to the crank spinning. So that will make one side a little heavier and the other side lighter.
Isaac Newton agrees with your hypothesis.
Another thing to think about is how much air is your turbo intakes sucking in? You can think of your exhaust adding downforce but what about the 2 huge vacuums you have facing up in the air? Just a thought..
Your (lack of) physics background is failing you here. Look at the basic rocket equation. Even if the turbos were oriented vertical there must be more energy coming out of the exhaust by definition. You've increased both the mass flow and the velocity.
@@otm646 An engine is just a big air pump that adds fuel. Air out requires same air in. No added mass.
Rocket engines either solid or liquid fueled do not use air. How else do they work in the vacuum of space, Doh!!!
@@otm646 wrong sir, you can't expel more exhaust than you intake, even if exhaust pressure is boosted by the turbos the effect is the turbos are taking in an equal amount of air. yes you have increased the mass flow and velocity but you've done it in both directions in and out of the engine
@@mikecamrcplus3057 you add fuel … there’s your added mass, during combustion fuel isn’t just “used up” it’s just an exothermic reaction with byproducts, mass is always conserved, also rocket engines have propellant and oxidisers as fuel …. Exactly the same as in a car, the oxygen in intake is your oxidiser and the fuel you add is your propellant.
@@timrobertson299 why are people nut understanding that what comes out the exhaust isn’t just the air the intakes consume your adding LOADs of fuel …. At an AFR of 3.5:1 on methanol, your literally adding in the region of 30% more mass in the form of fuel, the energy from the reaction is in the bonds between the molecules in the fuel, this isn’t a nuclear reaction, mass is conserved, therefore the byproducts coming out the exhaust must have more mass than the intake charge
Pretty sure your centrifugal force of the engine internals is moving the mass of the car away from the tires, via the shocks.. Notice once you let off and it idles back down, the weight goes up then back to rest.
I watched the video of the Croydon Racing R35 Pro mod, they talk about the weight balance and rotational torque of the motor moving the weight of the chassis.
Engine acting like a gyroscope
Pretty sure it’s the engine moving the body, flex from the torque.
its the engine acting like a lever against the sides of the car
Inertia from the rotating assembly is also a factor Steve. Also, top fuel is moving far more exhaust than silly methanol Motors.
Hey Steve, I have a few thoughts.
1. on many load sensors, vibrations and oscillations will cause lower readings due to their operation.
2. your intakes pointing up will somewhat negate the force created by the exhaust, but the exhaust is considerably more energetic so it should not cancel out or anything.
3. if the car is rocking side to side on the scales, they will not add to its true weight while it is still moving, due to inertial forces
All in all, I think this is just an issue of the scales and their readings.
If I was tasked with experimentally finding the exhaust force here, I would do it by measuring the exhaust gas pressure and velocity at the outlet and calculating the energy it would then exert on its container as if it was a tank of pressurized gas with a hole in the side.
Intakes pointing up was my thought too. next thing to try would be down or more realistically foreward angled intakes
Hi Steve
I think you need to remember the inlet of the turbos are lifting the car. The way your car is set up the inlet in the outlet are canceling each other out.
Was thinking the same. What goes in, must come out.
Rolls Royce Merlin had straight to side exhaust in the beginning. When they changed it to a ejector exhaust that directed gases rearwards, the exhaust gases made 70 pounds of thrust
I have seen that detailed in a book (WW2 Allied Piston Engines), you are correct. Unfortunately I gave to the book away as I'm not a plane guy.
Steve, I have tested this all before. The wastegates must point up as well. I have shock travel data that shows downward thrust till the gates open at 38psi, with gates pointed down, saw .3 in travel upward at around 100mph.....so they were actually negating the downforce of the car. This was with a “Back End”/ Street set up with 55% on the rear. But if you want more example, look at the FWD guys. They have every pipe out the hood. They found every-bit helps, and so,e say as much as 100lbs, idk about that haven’t tested that myself. I also know of 2 diff pro charger guys who have 3/4 sets of zombies for diff surface conditions, and they swap em often
Yeah, those zombies start to get pretty ripe after a while.
😋
@@iknklstgood comeback but give the guy a break for autocorrect. Also how many of us always proofread our comments until somebody calls us out on our error?
@@williamstamper442 You must be fun at parties.
I wonder if the wastegates actually cause more of an issue pointing down.
The underside of the car acts like a giant diaphragm (lever essentially) whereas the bullhorns are just going into the air
@@iknklst you better believe I am! And I go home with a smile😎
Engines also create a gyroscopic effect that can effect weight and balance slightly, It might be negating some of the weight gain from the bullhorns
I was looking for somebody to say this
This has always interested me. There is a reason for the top fuel cars to have certain angles for their zoomies. Also I know for a fact that, if you have a high HP vehicle going down the track next to the wall or barrier, with the exhaust pointing towards the wall it will push the vehicle opposite the wall. Also if the exhaust is dumped under the vehicle it will lift the vehicle. I’ve thought about this a lot, considering locations to vent my exhaust on my build.
Same. And I guess this is why F1 teams spend so much time and money on CFD. Intuitively, it must have some effect, and with top performance racing, every little helps. I don't know enough about engines, but am learning a lot from this channel and looks like nicksrandom's done some of the calculations. I guess next step could be to add suction with the air intakes under the car. But I'm pretty sure that would have less of an effect, plus the risk of ingesting garbage from the track. Or maybe a ballast system or sliding weight on rails so as the car launches, it dumps mass, or moves it to the rear. Somehow, I doubt track owners would be happy if the launch involved spewing lead shot over the track though.
Steve if you are feeling crazy here is something..
Add fuel injectors to your exhaust pipes, add jet nozzles with an ignitor right before the turbine. Replace all high temp parts after the nozzle with Inconel or other high temp metals. You can now theoretically power some of your turbo spool with fuel and get some good downforce coming out the tips. Basically some rocket powered turbos.
Or you can also spool the turbos completely with monopropellant like Turbonique used to do in the 60's.
I have made approximately zero calculations on if this would work, this is 100% based on "fuck it" science.
Love the videos keep them coming!
“Fuck it” science is the best science. 😂
now that's my kind of science!
Might need another hose clamp on the bullhorn.
Sounds similar to what some group B cars used to do for antilag back in the day
That's how Subaru does antilag in group B. If you use inconel type X (alloy X-750) it would hold up just fine. Run nitromethane for volume, and the exit needs to have a nozzle in order to quickly accelerate the exhaust gas in the opposite direction. That's fluid dynamics and energy conservation, with a little bit of chemistry and metallurgy.
Steve, many years ago a drag bike here in the UK "Jade Warrior" did some clever stuff with Bernoulli or venturi effect to gain downforce from the exhaust. It generated ridiculous down force, there are diagrams on the net showing it. The effect was so extreme that they had to disable it during burnouts. That was a 2 litre supercharged engine... I bet the same principle could be used....
I will do the maths challenge, but I do wonder if the car being lifted off the floor on the scales has reduced the pressure under the car? Maybe worth putting a manometer under the car? You are producing a lot of low density exhaust, no idea what the temperature is but I would guess close to 1300f? In which case the output volume could be about 4 times what you put in.... sorry I am not a dragracer... the weight of burnt fuel in the exhaust is also significant....
Jade was a nitro fueled machine, the majority of nitro burns out the exhaust on a full power run. There is a tremendous amount of thrust generated from that nitro burning in the exhaust. You can see the effects in super slow mo video on the body panels of funny cars. Most of the methanol is burned so the gasses are not still expanding near as much as with nitro. I'm not saying there is nothing there, but nitro is several orders of magnitude greater. Something blows folks hats off........There is force there!
Your input is very interesting. With that said, I believe what's needed here is first a method to actually measure any changes. After that then the "reasons" can be discussed. Am I making sense? Got a lot on my mind lately and that's when ones critical thinking skills can be reduced dramatically..
This is fun and all but if you suppose the exhaust is providing downforce like a jet engine you also have to take into account the air intake is also pointed straight up. If the intake and the exhaust of a jet are pointed the same direction (in your case both pointing up) its cancelled out. To measure the thrust you'd need to know the air speed going in and out of the turbine.
At some point I recall reading about exhaust being negligible in providing "thrust." However, there is a venturi effect that helps draw it from the pipe. Like a scavenging effect that provided more usable power than "thrust." This may be exclusive to 2-stroke engines though, as that's the core of my deep diving into exhaust modifications. However, I could see it applied in straight header 4-stroke as well.
The easiest way would be to use a gas flow meter to give you a cfm of flow then use that information to calculate the amount of gas pressure along with the exhaust gas temps at the bull horn. There is a calculation for this with many variables and information needed (ex. intake cfm, volumetric efficiency, exhaust temp, tube size and restriction, flow rate of the turbo turbine side)
Exhaust gas pressure and volume thru it's exit will not directly correlate to the kind of results this test is meant to show. Or maybe you are correct and there is not much to this idea. Either way it's gonna be interesting to see any results
I did the calcs, rough numbers and may have gotten it wrong but it's equates to about 2-3 pounds of thrust. The killer seems to be the 2x 5 inch diameter pipes, so much cross-sectional area for the flowrate. The engine pumps a lot of air but those pipes are huge. Not to mention what is "lost" through the wastegates.
@@heathmccarthy5137That really surprises me. My gut feeling would have been more like 30 to to 50 from an engine with that much power
@@Harry_Gersack at low boost and lower rpm’s and that large of a horn, in shouldn’t make that much down force. Top end of the track at full boost and 8800 rpm’s, the pressure may be greater. With the top fuel cars, they make so much down force from the exhaust (in theory) from the amount of fuel still being burnt in the exhaust pipe and the amount of pressure it is being forced out, on top of the pipe size. Under launch, they produce close to a 3 foot flame out of the exhaust tubes and under the run, it can affect the car as to push it to the left or right as it starts to lose cylinders. Pretty cool actually.
I agree If too much is affected by all the transitions. It needs to be measured at the point of exit. Just worry about the force then decide which direction to point it. You could point it straight up for the launch and straight back for the last half of the track. Just spitballen.
As you already know Steve your right on your hypothesis, this is the reason top fuel are limited on exhaust angles because the first team to angle their pipes found something like a tenth improvement in their time down track. Now all teams have their exhaust angled back to the limit allowed,your just using it as down force instead. Oops I should have waited future into vid
What you are saying is accurate...however you are comparing nitromethane fuel source to methanol. Nitro is so crazy powerful and harsh that the combustion event is still happening out the pipes! Nitro is actually comparatively slow to burn, takes a bunch of ignition lead to propagate a flame front as well as tons of electrical energy to light, even under compression. Once it does tho', violent things happen and the loudness is due to the combustion event continuing into the pipes. Once things are happy at a high rpm lighting off, it's almost as if those ridiculous exhaust pulses make down force from the sheer force of the explosion shock wave moving thru the air in our atmosphere.
With methanol, things are a bit more tame, in comparison.
Still tho, I did agree with your original comment
Hi Steve, I am studying Mechanical Engineering right now, so I don't consider myself an expert though I will try to provide a possible conclusion to your scenario. The only way to see a reasonable difference on the scales is to have an extremely high rate of flow (of fuel and/or exhaust gases) out of the bullhorn. A high rate of flow as such will actually generate a "downforce" that is GREATER than that of the weight (of fuel and/or exhaust gases) leaving the bullhorn. As a comparison we can use a rocket. If a scale is placed under a rocket and the rocket burns fuel and sends the exhaust gases downwards, the scale would read higher, however if the rocket does not burn fuel fast enough and does not send the exhaust gases down FASTER than the rate at which the fuel is burning, you will see a smaller number on the scale even though the exhaust gases are pointed at it. Looking at the other comments, yes, there is likely a small delay in between sampling time on the scales which could be skewing your information because of the motor shaking. It is also possible that the wastegate pointing downwards will have MORE of an effect than the exhaust as there is likely higher pressures in the wastegate than the exhaust. It would be interesting to see if you pointed the wastegate upwards and the exhuast downwards if you would then see the higher scale reading you are looking for. Overall, I honestly think the exhaust pressure (and maybe the wastegate pressure too) have an effect so small that I may even consider it negligible. All that being said, I could be wrong and maybe they have a bigger effect than what I can tell. Either way, if your looking for any edge over the competition you can get, I don't see a downside to pointing both wastegate and exhaust upwards.
I remember being a young graduate with my whole career ahead of me (honestly I wish I still had the enthusiasm and it was great to read your comment) but in 45 years read your comment
Good morning brother I really appreciate you and your videos have a awesome day everyone 🇺🇸🏁
Probably the best way to test it is on the track with your shock travel sensors and see the height difference and you can work out the extra load based on suspension travel. In the car and scales like the way you tested you may have too much vibration or engine torque going in to the transmission affecting results
I think you're right about the vibrations, but imo testing this on the track will give you a gut feel at best. I think there are too many variables to get an accurate result.
But yeah it would be easy to do it that way and at least give you a feel if it even does anything.
How do you calculate it on the track if acceleration throws all the weight back and aerodynamics begin too? 25 baffling people liked your idea though.
@williamherzog6920 if you did back to back runs, one with horn pointed back and one with it pointed down, wouldn't you be able to compare shock travel?
@@cheapscifi yes of course, but have you ever seen back to back runs from a car where there were no changes made between the runs? The time is never exactly the same. Which shows that there are a lot of variables in drag racing, even though it doesn't seem like that at first glance
Should be something like ~157 lbs of downforce total. Area of the 5 inch exhaust(19.6 sq inches) multiplied by the 8 pounds per square inch of pressure the engine is reading. At 50psi its closer to 980 lbs of downforce. This assumes all the flow is coming from the upturned exhaust, but in reality alot, if not most... is coming out the wastegates.
Most if not all digital scales are based on pressure transducers. Any vibration will mess with the measurement because they are not limited to 1 axis, which is why they all come with instructions to NOT drive the car onto them. You need an old school spring based way to measure it. Maybe lift the front end with spring based engine weight testers on 2 hoists, and measure it that way.
I agree with the vibration being the issue.
This is a little different but when weighing cattle individually on the same type of scale they read lighter when they move about excessively, even though all of their mass is on the platform and therefore on the scales.
I also wonder if the waste gate is cancelling out the exhaust to some extent with the exhaust being such a large opening and the gases escaping and dispersing, the effect is minimal.
Also that hot air coming of the exhaust, so it’s lighter.
All little things that might add up net zero effect.
You’re way off. You haven’t factored in that A the turbines extract all the energy from the gas flow, and B those pipes are not jet nozzles. That 5” inch tube is in fact much larger than the exit port of the turbine itself. There’s next to no energy in that exhaust. It would be like taking a T-55 out of a helicopter and expecting it to work asa jet engine. Nope, ain’t happening.
Something like the scale at the dump used to weight the difference before and after loading/unloading might work if that's the actual problem.
@@AB-80X its purely a function of the pressure at the exhaust exit and the area of the exhaust exit. The density of the 'fluid' also matters on both sides, but for a car engine, its basically air density.
Pressure ratio for a well fit turbo should be near 1:1 intake to exhaust pressure... thus the 8 PSI of boost is also exhaust pressure and is basically represents the added heat energy. This roughly matches with thrust I've seen from homemade car turbo based jet engines getting like 75 lb thrust out from 9psi on a s500 diesel turbo.
@@ImRichRu
You can’t compare the two. In your case you have a significant excess of energy in the gas flow. Try and put a power turbine behind that impeller and see what kind of thrust you get. Heck, a GE79 running at 70% throttle with the nozzle in reheat configuration has next to no thrust.
What nozzle is on that turbine when you create 75 lbs of thrust? If you don’t have a power turbine to remove the energy from the gas, then a tube with the same area as the turbine will function as a nozzle.
I think the problem is simple, it's mass flow of air, or air in air out. You only alter it's density by combustion but not its mass. The turbos are sucking up and the exhaust is blowing it down. IE: counteracting one another. Now your fuel type carries its own oxygen and therefor it should still have a slightly higher exhaust mass output vs input because of that. But that fuel mass was already accounted for via the scale weigh in, and it now gets sent out the exhaust so the car gets lighter...
One flaw I see in testing this, is the exhaust piping is going to flex itself before lifting the vehicle or shoving the vehicle back down. If you had a completely solid mount from the exhaust to the motor with no flex and a solid mount from the motor to the chasis with no flex, then you would be able to see the results you're expecting. Your piping is absorbing the change you're expecting the car to have. If you mounted the exhaust pipe directly with the chasis of the car you may get results? Didn't read all the comments so not sure if anyone brought up this point so sorry if I'm beating a dead horse
Putting a nozzle on the end of the pipe would almost definitely help make more thrust, only issue would be how much the flow can be restricted without negative effects
Maybe size the nozzle about the same size as the turbine wheel outlet. same mass and higher velocity means more force
Steve. Your turbo intakes are pulling weight off the car since they are aimed up. Drawing air from above the car and possibly pulling the car up. The wastegates are also pushing the car up. The only thing pushing the car down is the bullhorns and they are half of the intake….. maybe…..
Very logical in theory. I like it.
Steve youre not wrong. We played around with Zoomie angles as well but we found that the diameter of the headers played a bigger roll. We tried 2-3/4, 2-5/8 and 2-1/2 and landed on 2-1/2. We think it was more about the velocity. We also made 42 lbs of boost on the 2-step.
Point them down and see what it does.
Velocity from the 62mm gate will be higher than the velocity from the 5" bull horn. You might need to have the gate pointing up too if you want to maximise the effect but if it gets lighter pointing both down it will show the effect working - just backwards
It would take a LOT of exhaust pressure to affect the weight of the car the way its being exhausted upward. You would probably notice a difference if you aimed them down and had the tips almost touching the floor. The pressure would force the exhaust tube up which would lift the car.
Exactly, because the air above is not dense and the floor is.
Turn them so they point to the floor and see if you can measure a force when directed at a solid surface. If it does, you might have inadequate volume/velocity on the two-step to push against air. Or put the car on the dyno and make a run.
Was thinking the same thing, rather than measuring the weight of the car, measure the thrust directly. Scale under outlet.
@@SomeGuysGarage
If he wants any kind of meaningful A/B test, he needs to use the horns that face back. If he puts them close to the ground facing down, he creates additional pressure that was not there with the pipes facing back.
I read an article and the guy gave an in depth mathematical equation and concluded that a top fuel dragster would produce somewhere between 200-400 pounds of downforce from the exhaust. I reckon the best way to measure it would be to fit sensors to measure the front shock lengths then give it a hit with the bullhorns facing up and down to compare travel in the shock under full wide open power
As a jet engine mechanic, (no joke 23 years in the Air Force) thrust is best explained like a balloon when you let go of the opening and it takes off, but not because of the air coming out the opening it's the release of pressure within the balloon that is equal on all sides while holding the opening closed but is no longer equalized on the opposite side of the opening is what pushes the balloon. Having said that! in the combustion chamber the only thing that moves or relieves the pressure is the piston so there is thrust applied to the heads which are pointed up not down.
It’s the shocks. If your shocks were replaced with straight steel I bet that would make a difference. Love the channel Steve, keep it goin man!!!
The force they're feeling here compared to a launch? End of the day scales at the tire, tire won't move if the shock says no, and they're laughing at this attempt.
Good call. Probably the compression on the shocks.
The shocks don't matter. Any force they absorb is countered by the normal force at their attachment points. Newton's 3rd law- equal and opposite forces.
Most of the exhaust pressure is used up as it flows across the turbos. The energy is extracted from it by the impeller in building the boost.
This same effect doesn't apply in a blower setup, there's no obstruction in the exhaust, that's why there's so much left for the zoomie style pipes.
Edit: think of it as analogous to voltage across a resistor or any electrical load, that's why it's called _"voltage drop"_ on the other side of a load there's less voltage left. _The turbo is the load/resistance._
@@dougfry5897but if the turbine is using up the mechanical energy from the exhaust flow… all that is coming out the pipe is just used up exhaust that doesn’t have enough energy to be measured…
@dougfry5897 Modern jet engines are all high and now ultra high bypass...over 80% of the thrust comes from the bypass air and not the core. One other important point with a turbofan...they have a nozzle to accelerate the core exhaust. I've vastly over simplified it but you get the jist. 😁
@@dougfry5897 Without boring the pants off you... In simple terms...no nozzle= no acceleration of the stream...a simple way to test that theory... turn those exhausts to face rearward and see if the car moves while at full throttle without the rear wheels providing any drive.. The answer will be, not without a hill!
There is a reason you don't see every backyard engineer building turbojets from old turbochargers.
Their function in life is to use as much energy as possible to drive the compressor while having an acceptable pressure ratio.
Once you've used as much of that exhaust energy as possible it's work is done....If a nozzle was placed downstream to re accelerate the exhaust stream it still wouldn't produce jack in the way of usable thrust as you've already taken most of the thermal energy being produced to drive the turbine... Adding that nozzle would simply serve as a restriction resulting in less power from the engine.
@@Super_64 I’m guessing with your opinion, then you would not mind leaning over the bullhorn and looking into it at full throttle
@@garystat 😂😂bahaha, Not advisable! But then I wouldn't do that with a heat gun either and that's not going double as a jet pack.
Steve its about thrust and nozzle size. To really benefit you would have to design a complete set of headers that would let as much air pass out them as possible, we as much thrust as possible. But just putting the motor on the two step is not going to produce as much thrust. Mike Murillo did alot of research into this and found that when he moved his bull horns the car did not hit the bars as hard so he could leave a little harder but the real benefit is down track. I would spend some time testing and try turning them slightly pass 90 degrees towards the back or side mirrors. When the motor is producing the thrust it will push the front down and forward under track conditions. I learned this bunch of years ago from a guy that built my first set of custom zoomies for my race truck. The ones I had were the wrong size (to Big) and did not turn up and back towards the side mirrors if it would have had them there were straight up. Good experiment.
The sound pressure from the bull horns strike the ceiling of the shop with enough force to push the shop upward. As with the Earth rotating and a person jumping in place and coming down in the same spot, your car and everything around it is going in the same direction, therefore, it doesn't register on the scales. No Bud Light was abused to calculate this theory.
If you know the flow rate through your engine and the temp of the exhaust, diameter of the exhaust pipe etc. you can find the velocity of the exhaust and calculate how much force
He asked for you to calculate it and report back.(you do the work for him)
Wouldn't the intake pipes on the turbo's counteract the exhaust to some extent?
Yea came here to say the intake pointing up would cancel out some but not all energy. Pointing the intake down would definitely improve the downforce a tiny bit
I hope you make it to World Cup Finals next year! I'll be there to watch and buy merch if you are!
When the motor is spinning the mass of the rotating components remains the same but thier influence and inertia is no longer governed solely by gravity and this counteracts the effect on the scales from you exhaust. The "thrust " downwards is still substantial and worth having (every little helps) but as your car remains the same mass but at the same time lighter you can't measure with scales without a calculated correction factor . Takes a bit of getting your head around the gravity / weight and mass thing but you can balance a crank so the light bulb is already on , just the other side of the workshop.
Great content by the way
I’ve wanted to see someone test this for long time. In NPK, Murder Nova had one of the exhaust horns off during a run and he could “drastically” tell the difference. I would guess that the waste gates are counter acting. Maybe if they were angled up as well.
No, the difference came from air moving across them when traveling at full speed (like a wing/spoiler).
We can do the math here based on the mass flow through the engine.
I suspect it isn't a huge amount but you are at the point where a 1% gain somewhere makes a difference
I need to know fuel consumption to roughly estimate based on cr and displacement
Those scales probably aren't sensitive enough to pic up the small amount of force created by either
The exhaust pressure is pushing against every inch of the the entire exhaust system. The entire system would need to be shaped like a rocket nozzle if you wanted to get significant thrust from exhaust pressure.
If you make the final size of the horn a smaller diameter you will have more pressure coming out of the pipe. Pressure increases as resistance to flow increases. I suspect that angling the horn at a 45 degree would probably cause more down force on the track due to wind resistance compared to pointing them straight up.
More pressure reduces flow. That would be detrimental. You need pressure AND volume to move mountains, such as the 3600something pound wagon
Wrong …If the tube gets smaller the pressure reduces and velocity increases.
I wonder if the upward suction force from the intake counteracts the exhaust somehow.
It certainly does to at least some extent. That was one of my first thoughts as well. And since the methanol stoichiometric ratio is 6.4:1, that would seem to indicate that 1/6 of the thrust created by the total exhaust volume is being counteracted by the suction of the intake. Possibly even more depending on the difference in flow velocity, since physics tell us that Energy is equal to mass times velocity. And i'm gonna bet that a turbo spinning at 85,000rpm is creating some impressive intake velocity at the inlet
It does
I think we're also forgetting about centrifugal force within the rotating mass (crank only in this case since the drive shaft is not engaged), negating some of the weight the faster it spins.
You nailed it, considering the size/weight of the his engines and the acceleration/deceleration of the rotating components I bet they’d be surprised at the numbers of the forces at play here
I would suggest putting the chassis on the scales. The down force may be getting transferred into the strut springs and not transferred through the tires (which are also springs) to the scales.
If you put a pressure gage in the pipe and then calculate the flow based on engine speed and volume, you could determine flow rate.
The thrust of a jet is massflow*jet velocity. The massflow is the weight of the exhaust volume produced per time unit:
rho*V*revs/2,
where rho is the exhaust density and V the engine capacity. The jet velocity v is the speed by which the exhausts exit the pipe, so the thrust is
rho*V*revs/2*v.
Just to get a rough estimate, use rho = 1.23 kg/^m^3 (density of air, exhaust is heavier, but not by a lot with gas as the fuel), V = 0.003 m^3, revs=300/sec, and v=300 m/s and multiply.
Then you get
1.23*0.003*150*300 = 170 N.
So the peak thrust is on the order of 200 N or so (corresponding to a "20 kg" or "40 lbs" downforce), which is not a lot.
So let’s look at it volumewise. 540 cu inch, but only every other rev is an exhaust cycle, so 270 cuin at 5200 rpm times 1.6 to account for boost, then divide by 1728 to go from cuin to cuft. You get 1300 cfm, of air input. Gasoline engine expansion ratios are about 12:1 on the higher end. So 15600 cfm of outflow. Thru dual 5” pipes you get about 162 mph wind speed. Which may seem like a bit, and enough to blow hats off, but every 60 mph only generates .06 psi of dynamic pressure on a near surface. So with about 40 sq inches of pipe if it was acting against, say the floor, it would generate about 6.48 lbs of thrust. That 1200 hp is going into the converter to do work and the waste is coming out the exhaust. it’s not a 1200 hp air mover.
I like this. An attempt to get real math and physics involved not educated guesses. You’re on to something.
maybe it needs to be thought of a bit more like a flow bench... measure the exhaust velocity (anemometer or pitot), the orifice size (the pipe area) and rather than a measured depression and calculated airflow in cfm, you invert the equation with a calculated cfm number to give positive discharge pressure (as opposed to the depression of a bench) at the pipe
everyone else has mentioned any vibrations affecting the accuracy of the scales for direct measurement, there are load cells you can get to measure thrust, once the load cell was 0.25D above the outlet it wouldn't be affecting the curtain area or offering any restriction to flow
@@stevececchele2880 a digital manometer which is normally an hvac tool will measure the pressure differential at the exhaust and ambient. He should just buy one if he doesn’t have one as it gives you a perfect number for pressure loss through an air filter which can come in handy. I think the consensus is going to be that it’s not as much force as people think. It will be more under full whack, and certainly “something” as he’s wrestling with which makes it useful to aim it where he would like it to go, but a lot of exhaust is going to get used up filling the vacuum space along the side of the car once it gets moving, and not necessarily generating a ton of down force. But still, every little bit counts in that game. The fun part is to think that with 150 psi of backpressure to make 70 psi of boost, there's about 2000 lbs of force on that turbo exhaust flange, yet we're talking much smaller numbers here on the other side of it. But that's just a turbo doing what it does, recovering energy.
@@dochaze1 agreed it wont be very much, rather like the guy above saying 20kg of force... although in his example I think he was working on just one discharge (outlet) whereas there are two, so cfm needs to be halved again (two turbos and two outlets)
I also think the cfm number would need to be temperature corrected (Boyles gas equation) too, as temp has a huge effect on air density / speed.
people saying it won't generate force as it's pushing against air are wrong... think of a rocket, sure it overcomes the most resistance to movement at liftoff when pushing against something solid, but when it's in flight it's still thrusting and pushing against only air.
same with people thinking the inlet "suction" and the exhaust "thrust" cancel each other out... if the exhaust was at ambient temp then they are probably correct, but a big chunk of energy has been added to the exhaust gas from the combustion process....
Hi Steve cool experiment. From what I recall from thermal dynamics, the down force correlates with the mass flow rate and velocity out the exhaust. Since your burning so little fuel on the two step your not getting near much mass flow rate out of the exhaust as you are when under power. Sorry I don’t know the formulas, but can you compare the fuel rates on the two step verse’s going down the track.
It's all about pressure. Thrust essentially works by decompressing a gas to the atmosphere (think fire extinguisher). Piston engines are designed to convert as much gas pressure into mechanical energy in the combustion chamber and out the crank as it possibly can. In fact, a turbo does this even more, it converts exhaust pressure and heat back into mechanical energy to pump more pressure INTO the engine than what is coming OUT of it, to be converted back to mechanical energy in the crank. It doesn't matter if the engine is 3 or 3,000 hp, all that does is increase how much exhaust gas is pushed out at just above atmospheric pressure and essentially no thrust is created.
@@DopetheWind Its all about mass flow
@@DopetheWindYou know that the best combustion engines trimmed for efficiency have about 30 - 40% right. Now guess the effiency of a 4000hp drag racing engine that doesn't care about fuel consumption at all. And the rest of that energy is converted to heat --> exhaust.
And relevant for the thrust are mass flow and velocity, not pressure
@@DopetheWindAlso go to a dragstrip with a piece of cardbord and just hold it into the exhaust flow when one these things launch (there are enough cars where the exhaust is pointed sideways).
You will feel a significant amount of thrust trying to blow that thing out of your hands
@@heathmccarthy5137 I think you're making a good point. Also there is no significant load on the engine
Simple test: Measure with the exhaust pointed down, then measure with the exhaust pointed up.
Any air going down will create a strong upward ground-effect, building high pressure under the car, somewhat like sitting on top of a balloon.
Best of my knowledge, the amount of exhaust on the 2step is just a tiny fraction of the exhaust under load, but to get any thrust you would probably have to taper the exhaust tip to create a nozzle.
I dissagree with everyone saying that the intake is pulling up more than the exhaust is pushing down simply because the volume and velocity are much smaller at the intake (valveless pulsejets intake and exhaust both face backward)
Hi Steve
Here's my 2 cents. Think of your exhaust like a turbine exhaust. To make thrust (force) you need to narrow the exit, like the vanes on an afterburner.
Yeah thats true for turbine's, that are designed for creating thrust. The engine need's to flow for better gains. You don't wanna have back pressure last I heard anyway.
I think you'd see something tangible on a screw blower car. Remember, the turbo is there to take energy out of the exhaust. That wastegate is behind the turbo so it sees the full enchilada of exhaust energy.
feed the wastegate back to the exhaust maybe? However, I don't think that, with all things being equal as far as mass air flow into the engine, a supercharger or turbo would produce less or more thrust. The way I see it, if the mass airflow in is the same, the mass air flow out is the same (again assuming you can route the wastegate back to the exhaust)
that is an astute observation
This has always been a theory of mine, i think i originally seen it in a funny car video explaining how the exhaust creates down force, then i would see foxbodys doing wheelies but the guys with a bullhorn setup like this weren't doing wheelies and got clean launches. It was interesting. I always wondered the exact effect like this.
Two things you might consider Steve:
1 - The engine rotation might "twist" the whole car chassis, making it lighter on one side and heavier on the other more expressively than the exhaust pressure.
2 - Would the shocks travel log show anything?
I think top fuel downforce is about 100 pounds per primary, and I agree you should do it on a hub dyno. Front shock travel changes should be beneficial but give only “relative” information and not absolute (pounds of downforce). If I had to guess, I’d guess your downforce would be about a third of that as a top fuel car, so would expect about 200-250 pounds of potential downforce assuming exhaust is not being offset by something else.
Well Steve, there are multiple ways to do this. I believe the result you're looking for is going to have to be full load though. The easiest way that I would try first is on the hub dyno with those scales you were using. Make a pull with the exhaust exiting parallel to the floor, even the waste gate exhaust and then a pull with it straight up. Another wound be pretty much the same method but using a load cell attached to the floor and the chassis, centerline of the bull horns. You could put load cells on your suspension and go to the track. Another way is the bull horn to have the ability to freely move up and down with a load cell positioned underneath and centerline of the exhaust exit. Just my $0.02
Precisely what I was thinking! Needs to be done on the hub dyno!
I agree that the hub dyno is the way to go. Doing the two step is not a good way of testing it. However, when it’s on the hub dyno, the front end lifts way up typically due to the weight transfer. I guess you need to do it with the horns pointed down and then pointed up and see what the difference is.
On the 2 step your just make enough power to spool the turbos. Figure out your sq. in. of area of you bull horns, then figure the area of 4 fuel headers, fuel car 11,000 hp vs. what ever you dial in. 2 different animals, you are restricted by back pressure, blower motors are not, a ton of your power is used spinning the compressor, blower motors steal that power from the crank, that is why turbos are more efficient, your not getting the energy because it's used up before the bull horns, you made em big to reduce back pressure. Need to ck it under load on the hub dyno. That's my story and I'm sticking to it!
@@montestu5502 yes it does lift but I don't think it lifts the tires all the way off of the floor though. You'd need to direct exhaust outward so it cancels out, neither lift nore down force.
@@ch3no2killz you are correct, turbo exhaust will never make as much force but it does some. Plenty of hobbiest and myself have made jet engines from turbochargers. This is basically the same except the SMX is the combustor. You are correct about the diameter of the bull horns, they would need to be necked down just like a nozzle on a jet engine.
Where force is being directed and what is resisting that force is important. Given the opposing directions of the air flow/forces between the waste gate and exhaust + differential nature of the resistance the air from each meets + the nature of a 2-step balancing flow between the two to hit the desired boost level, there is a very good chance those forces are largely offsetting each other making it very difficult to measure the impact, if any.
It might be interesting to take current results (wastegate down, bull horn up), and compare them to wastegate down, bull horn down. This would give you an idea of total potential lift. While the downforce would be less with the bull horn up (only pushing against air and not the ground) you would have a ballpark expectation of the downforce if everything were reversed. You could then test the impact of the wastegate flow being directed rearward, then see what happens when rotating the bull horn into the vertical position.
As far as solving the wheelie problem in general, if you really want to go down the physics rabbit hole it might be worth looking into precession of a gyroscope. You know the feeling from holding an angle grinder at high RPM - it feels somewhat difficult to move in certain directions (perpendicular to the axis of rotation), and doing so makes the grinder want to pull in a different direction. You can also see this when you rev an engine and it dips to one side - the forces from the pistons are acting perpendicular to the rotation of the crank, so torque that should be going through the crank gets redirected off axis.
That said, there are a lot of things mounted around the same parallel axis of rotation perpendicular to the axis of rotation of the rear wheels (crank, trans, converter, driveshaft, turbos, etc.). I'd wager this is causing much more torque to be redirected upward than you'd expect, in part due to the slight angle the crankshaft and turbos are mounted at currently only being made more severe as the rear squats and the nose lifts on launch. You obviously can't do much about things like the crank other than making them lighter. That said, given the much higher RPM of the turbos, re-orienting them so the axis of rotation isn't perpendicular to the rear tires may reduce the torque being redirected upward, which may be enough to keep the nose planted or at least reduce the weight on the nose required to do so.
The thing with the bull burn exhaust was explained to me as a child to the tune of
Due to the air flow as the car moves forward the exhaust changes the flow of the air passing by the car creating down force
Hi Steve, I believe it might also have something to do with air density, the air moving accross the bullhorns at 200mph will be a lot denser and would create a lot more down force...
Just my 5c...
Love the Channel!
I also had that thought. Probably the downforce will not be that significant in the 60ft
Hi Steve. I was thinking that since the intake for the Turbo is pointed up, the same amount of air that is getting blown out upwards would be the same amount of air being sucked down into the turbo, meaning they cancel each other out. I might be totally wrong but it makes sense in my mind.
Was thinking the same thing, the turbo´s will lift the car and the exhaust will push it down the way the pipes are pointing.
This is the answer. The engine is one big air pump. There's undoubtedly a difference between the intake and exhaust with the heat fuel added but it's a small difference.
Exactly
Well since the Air/Fuel Ratio is probably 4:1 the exhaust will be 20% more air mass leaving the exhaust. So that will be the difference. If the air was coming in from the front or below creating a vacuum and the exhaust was up you'd get double the benefit.
Yessir! I'm glad someone mentioned it before I did
Love the technical stuff 🤜🤛
I am always interested to see what Steve and crew got cookin up though.
The only way it could work is using your hub dyno, I suggest 5 runs with stock position and 5 runs with modified position. You don't lock down the front anyways, so perfect way to measure any downforce
The top part was after the initial testing. I still think it's the only way to measure it. i say do a 1/4 mile run like you were lined up just have the scales under the front wheels. 5 runs with the original position and 5 runs with the new proposed position.
I think the car needs to be moving as the car speed increases, it creates a pressure wave, not just over the top, but around the sides, where the exhaust will be pushing down against
It’s counter to instinct but exhaust doesn’t need to “push down against” anything. Newtons 3rd law. Same reason rocket motors work in a vacuum.
@@Matt_Vanepps think you got it wrong/mixed, the exhaust should push the car down exactly because of Newton's 3rd law, you can't have air/energy going out in one direction without having an opposite force pushing the other way, which is exactly why rockets work in space, you're throwing energy out behind the rocket moving it in the opposite direction.
Another factor to consider is that one of your original goals with exhaust is to freely move it out of the engine. After all engines are air pumps right? You are making HP by moving the most air possible and translating that into crankshaft rotation and torque. So you have 5” outlets to help do all that. Those same outlets also serve to limit thrust by their big open design. To increase thrust you would need a nozzle design similar to a jet engine which has the goal of producing max thrust for propulsion. And limiting your exhaust flow by nozzle design would be counter to producing max HP and torque at the crankshaft. As you neck down air flow through a section its output speeds up producing thrust but at a cost. So keep on making big power the old fashion way with the SMX and aim your bullhorns so they look cool and don’t damage the car body.
Steve, I did comment below, as did many others, your test did surprise me, your bullhorns have a total cross section of about 40 square inches combined though the gas exit speed was not as high as I was expecting. The result on the scales was very puzzling... I am sure we have all seen stuff blowing around in dyno rooms.
The exhaust is pushing down but the intake of the turbos are also facing up cancelling the effect of the exhaust. Also maybe the engine is acting like a gyroscope negating the downward force of the exhaust.
I think you may be correct. The intake is pulling just as much air in as the exhaust is pushing out. They are exerting the same pressure in opposite directions therefore canceling eachother out. Interesting take.
@@davidbronson3800 dumb question but isnt the mass flow coming out of the exhaust always bigger than that going into the intake? All of the fuel that is injected and then burned has to also be ejected through the exhaust. (air out = air in + fuel)
@@Max_xaM I think the net difference is negligible as shown by the scales. The same amount of air coming in is the same amount of air coming out albeit heated and expanded/less dense. No new air is being "created" during combustion and the small amount of fuel being added isn't going to move the scale.
The problem with digital anything is its refresh rate. The scales can not show the change likely due to them not refreshing as fast as each pulse exits the pipe.
Side note depending on your intake point ( angle ) it can also change pressure to the ground.
If the brace point of exhaust is parallel with the ground the force would not be down but side to side or front to back.
This is also why for a short few years motorcycle TT exhaust was pointed out under the tail at the angle it was even though it required more pipe ( weight ) to get it to do so.
First guy to invent ani-wheelie thrusters!!
~2000 Horsepower WWII aircraft engines developed significant thrust from their exhaust. Most of those were supercharged, though and the Turbo undoubtedly recovers a lot of the exhaust energy
I think the pistons and crank create a gyroscope effect to reduce weight.
Maybe the exiting air is not pushing against anything that is a hard stop. Turn the exhaust tips straight to the floor and redo your test, I bet the car will get lighter
This is what I was thinking also. There is no "hard point" against which the exhaust thrust is able to "push" against.
No need to push against anything. That's why rockets still work in a vacuum.
@@wingracer1614 rockets also have a nozzle to force the exiting thrust through a smaller opening to accelerate the hot gasses into a high velocity stream.
@@jwright650 I am aware of this. It has absolutely nothing to do with what you posted which is a very common misconception. Thrust in the form of a fluid mass being forced out of some pipe or orifice does not need anything to push against.
The reason things seem to push harder as they near a solid object is something entirely different from thrust. As an object approaches the opening, it creates resistance to flow and thus increases pressure inside the pipe. Since pressure pushes equally in all directions, it inevitably pushes on said object as well.
you'll probably find that the vibrations interfere with the sampling rate of the scales and make it hard to get useful readings, but under these conditions it will be hard to get much thrust out the exhausts in general. The thrust depends on the mass flow and the gas velocity, which depends on the pressure.
The turbo outlets are at a very low pressure until you're getting close to the flow limit of those pipes.
The wastegates are venting much higher pressure gas since it's before the turbine, so the exit velocity is much higher and more thrust is generated.
Think of the difference in force you feel holding a pressure washer nozzle vs a garden hose - even though the hose is probably flowing more water.
There will also be some lift from the turbo inlet pipes.
i think something that would help is shrinking the size of your exhaust piping. you're not going to get as much velocity from a 5in pipe as you would from something half that. you might need to drop down to something close to the diameter of the stock exhaust to get what you're after, but at that point you'd be choking out your turbos and sacrificing horsepower... i know there's a solution though, because i've heard that during WW2 the Army Air Corps put special exhaust tips on P51 Mustangs to get higher flight velocities - they acted almost like mini jet nozzles.
I suggest you put tapered fittings that reduce the exhaust diameter to 1½", that will increase gas velocity and push down.👍
that's what i was thinking. he might not need to go down that far tho to see the results he's looking for.
Velocity isn’t important. What’s important is flow rate and density. The reduction in cross-sectional area will increase velocity, but it’ll also restrict total flow. You’d see a net reduction in force.
@@JakeRobb I agree, but that would make a difference.
@@JakeRobb we are literally getting into rocket science here, but velocity is very much a component of thrust. A rocket engine is effectively the controller release of expending gas. There is a balancing act to consider in rocket nozzle design. Yes, some restriction does decrease your mass flow rate, but the increase in velocity can have a greater effect on thrust than the reduced mass flow lowers thrust. Taking a look at the cross section of a rocket nozzle may help explain this. Caveat, I am a mechanical engineer, not rocket scientist, but have a basic understanding of rocket motor design.
@@USAfor110thCountry I don't say it will help to go faster.
You've got the air volume, you just need to maximize its exit velocity. Adding a "nozzle" might create the effect you are looking for.
Not even a jack-leg engineer but I've done a crap-load of reading in all sorts of fields. There are a few things that could be giving the confusing readings. The waste-gates giving "lift" while the exhaust is pushing back down could be part of it. An "easy" test of that would be some plumbing to route the waste gate gasses to the sides and then see if the down-force increases. A related thought comes from hovercraft design, it's possible that while running, the waste gates are helping to pressurize the air under the car increasing the lift. Again, venting the waste gate gasses to the sides or even just the REAR of the car could counter that effect.
Another idea is literally getting into "rocket science" and I'm not even sure if it would be allowed under the rules you race by. Design the bull horns like ROCKET NOZZLES! With a constriction in the pipe and then a flaring bell for the actual outlet. That may result in unacceptable back pressure though.
A coupla things...
1. what is the diameter of the horn at the bottom versus the diameter at the top? (reference the Bernoulli principle) About them fueler rules - did you notice that the pipes on a fueler are constant radius?
2. there is an alter nate method that will give you a 'ballpark' value of downforce. It will be about as accurate as duck hunting with a blindfold, but will be fun and impress your friends. Weld a 1 inch square to the end of a rod, put a pivot point at the exact middle of the rod, place the square at the top of the horn, put a scale at the other end of the rod, crank up the engine and read the value on the scale. This will be VERY inaccurate but will show if you are in the range of 5psi or 50psi. It should vary greatly depending on what part of the horn you are placing the square. Multiply the value by the number of square inches at the outlet and you will have a rough estimate of the downforce.
It makes sense that the wastegates will have a large effect. Might collect more useful data during a hub dyno pull with scales. You'll probably want to plot the scale values so you can look at trends better. That said I would guess that more length on the end of the bullhorn would improve downforce by reducing turbulence.
Simple: Instrument the Bull Horn mounting point with a load cell. You'd need a flex joint to allow a little free movement.
All that I can think of is the mythbusters episode when Jamie and Adam had a myth about a ship blowing it's own sail.
Thinking about the energy in the fluid (exhaust gas), two things strike me, when you are leaning on it off the line the volumetric flow will be far higher, and you will be adding a heck of a lot more energy (fuel).
This is probably where your missing thrust is.
Also the intakes are facing upward, so at low fuel that will have a balancing effect too.
I haven't read any of the comments, but my thoughts are the affect you're looking for is notice / calculated moving forward not standing . Especially 4khp engines. Illegal Pipe angle > highspeed = slight increase in downforce =potential Victory!! Angled downward in front might lead to slight wheel lift with high hp vehicles. Computer/Simulated calculations or sensors' mounted throughout vehicle measuring + downforce at various exhaust angles.