How 2 stroke exhausts work
Вставка
- Опубліковано 22 лип 2024
- The first video in probably 2 or 3. In this video we look at the very basic concept of how back pressure works in 2 stroke expansion pipes. Firstly I talk about pressure waves, and show a simplistic version of how a pressure wave travels through a directional flow.
Excellent prognosis from young guy with interest in 2 Stoke’s .keeping 2strokes alive
This is the better version of Engineering Explained.
I duno, I'd go for "they're two sides of the same coin". It'd be fucking great to get them together.
true, I see your point
Alright fanboy. This channel has a better vibe, Matt is funnier that Jason. Also, Jason does a lot of sponsored videos where he tries to sell Shell Oil.
Triggered.
Jason is funny? I mean his preteen voice crack makes me chuckle sometimes
Found this channel very recently... utterly fascinating.
In kart racing (80's) we saw sliding exhausts, lengthened and locked long by a brake connected cable & pawl when the brakes were applied, released by depressing the throttle to the stop. The pipes we used just had a sliding convergent cone with a locating collar (held by self tappers from outside)within the parallel section. (Between divergent cone and stinger). We could adjust this in the pits whilst experimenting with header length and gearing changes :)
Greatly explained.
Going down the 2T rabbit hole
Ahh the good old 2 stroke days. Cuttin skirts, filing ports. I miss the smell. Konig had some racing outboards that had a sliding pipe setup on the inlet side of the expansion chamber. Could be slid back and forth with a leaver next to the driver.
Nice work Knackers! The people on escalator explanation to differentiate flow and density was mint.
I need to get on with my day, but I’m loving these vids.
Thumpers for life!
Wow that was a great explanation on how expansion chamber works. I've read it in some books I like the way you described it. Thank you for sharing
Great explanation! If somebody like you have come accross when I was studying engineering I would probably have stayed closer to mechanical engineering. Congrats mate!
Cheers dude - matt
thanks for the videos your explanations help me to visualize how this works,i once made an expansion chamber exhaust system for my Yamaha rt 180, it actually had 2 power bands first would start to drop off and a shorter one would hit taking it to its final rpm.Sure felt strange but was fun.
Wish I had teachers at school like you back in the day.
Very well explained thanks for that masterpiece info. Cheers
Yo i wish you were my math teacher... your whiteboard skills are infinitely better than any teacher i had. Maybe i wouldn't have failed math lol
Very well explained, thank you for sharing it, definitely thumbs up.
Cheers dude and welcome to the channel - matt
That variable length expansion chamber idea it’s actually brilliant . If there was a way to make it work efficiently that would be sweet .
people have tried - the main issue is reliability - the exhaust is hot and you need an air tight system that can take the heat (thermal expansion) and all the carbon and shit and still work time and time again
Thank you for the great video! Learned very much :)
hi, great vid. there is an easier way to adjust the pressure wave in an expansion chamber. the reflected wave is , to some extent governed by the diameter of the outlet to the stinger and this could be adjusted using an "iris" valve , similar to the aperture adjustment on a camera. just a thought, somebody will no doubt kick holes in it, cheers.
If you want to see pressure waves, watch artillery or explosions in slo-mo.. it's like a translucent supersonic bubble.
What about the properties of sound and mass? That "bang" sound generates frequencies that are bouncing around in that expansion chamber like the exhaust pressure waves are. Unlike the exhaust, it's energy, not mass but requires mass to exist, move. That same dependence for existence (mass) is what will eventually consume it. Both change when contact is made. Mass just bounces off each other but sound frequencies can bounce off of, viberate through or get absorbed by mass depending on the density and composition of the mass and the frequency and volume of the sound.
you take time to explain a very simple thing.
Quality videos mate, learnt fair bit from you vids
No worries mate thankd for the comment - matt
Thank you for the great explanation!
Thanks for the comment dude - matt
Check out CVEC exhaust pipes for nitro RC engines, I've had one of these pipes before. It's a tunable 2 stroke pipe. It has threads inside that holds a baffle like a firearm suppressor. Twist the baffle and it moves inside the pipe. Then you screw the pipe back together. It has 3 pieces. Two pipe halves and a baffle.
Thanks again for your explanation.
Really good explanation. Thanks. I now think I see why putting AllSpeeds on my RD 400 gave it more power, but made it very peaky compared with stock exhaust?
This video is very very helping.....thank you to explain in detail.....✌
No worries dude
Just curious.. some pipes will be more for low end power (fmf fatty), or high end revs, (fmf gnarly). How can they change that (increasing power at different ranges) or is it just the timing of waves at different rpms?
Brilliant mate just found your channel cheers
Welcome to the freak show dude, glad to have to along - matt
Good video, for sure... Thank you!
That ice cream truck sounds like the stuff of nightmares
Excellent explanation, this long time 4 stroke mech. thinks...
Just subscribed .... Very Well explained ...
your fantastic at explaining thing in a way i can understand!
cheers for the comment dude - matt
I finally understood it!! Thanks!
can You suggest good Expansion pipe measure value for my Yamha Rx 135 bike If you have any excle sheet to derive at t perfect values please share
Good vid , all credits to Kadan , the MZ godfather ✌🏻
Could You explain (if it's explainable) why 4-strokes don't have such expansion pipes? I guess it's all about the fact You get twice the pressure waves as in 4-stroke, but could You put more light on this?
David Vermillion has the perfect question for you to sum up all the component concepts you have explained.
Just as a note dont get confused normally the ideal gas law and uncompressible flow would dictate that a divergent nozzle increases pressure but decreases flow and a convergent nozzle would do the opposite. These are the assumptions when designing a nozzle for a rocket engine or most other applications. Here we are dealing with a compressible flow wich is quite a lot harder to simulate and design a nozzle for. In Rocket engines the pressures are so high that compressible flow isnt really a concern, here you would rather consider pressure shockwaves in supersonic flows.
help!, my yz125 has a nasty bog to it (mikuni tmx 38 carb) if im riding in high gear just cruising along, if a slam the throttle all the way down fast the bike bogs, but when i gradually increase the throttle bike pulls fine. Please HELP
I dont have much experience, but no type of engine is obsolete IMO, they are all useful for different reasons ready to be reinvented again anytime.
Great video, thanks alot.
What happens if someone's chamber has the belly or the constant diameter cylinder a big one, I read somewhere that the rpm range will be a high powerband, but not pick power.
Something to think about....expansion chamber can have the volume changed by having a port out of the headpipe going to stringer (bypassing the cones), controlled by a solenoid or mechanically actuated flapper valve. This can effectively change the reversion characteristics, depending on RPMs.
Hi , could you possibly do a video explaining ignition timings on a single cylinder 2stroke engine such as the dt125r, TDR125, tzr125.
Regards
Matt not related to this video. But have you done one on valve clearance. Manufactures say every 16k for my bike what’s your opinion ?
Perhaps, building a system similar to a thermostat within the expansion chamber. Great discussion, by the way.
Could you drive a 2t engine with a pierced exhaust?
Maybe a possibility is a metal diaphragm type expansion chamber that elongates and contracts with temperature/pressure.
Brilliant, thanks
So, if I may ask, I have a stock 75 Yamaha RD250 and it has its stock pipes on it... Since 2 strokes work off pressure waves, how does a relatively straight, baffled exhaust work? Is it the baffles providing the pressure waves? Or is it a simple means to an end without a true performance gain?
It's a simple means to an end, yes. Lots of older 2-strokes have straight pipes with no real expansion chamber simply to keep them less powerful, simpler to manufacture, and more "reliable" due to lessened peak power output.
Hi Matt, since I bought me a Gogogoped a few Days ago, I stumbled across this Video again. You mentioned a Seal for a very hot and dirty Environment in the Exhaustcamber... why not just use one or two big Pistonrings? Oil should be no real Problem, since in some Cases it pisses out the Endcan anyway and leaves black Marks all over the Exhaust.
Cheers Dude.
The "slow rebond" were there are fuel in the exhuast, is that why the Suzuki GT 380 has a refuel injection ?
How’s come 125cc dirt bikes exhaust pipes come out the cylinder then turn around the frame and go out the back, where 250cc dirt bikes come out the cylinder, turn left, loop back to the right and out the back? I’ve always wondered
its about the length of the expansion chamber and bigger bore engine needs bigger and longer chamber to handle more gas than smaller engines pipe, hard to explain because i´m not native english speaker so somebody else can explain better
So what is the benefit of having each cylinder go to its own muffler? I understand seperate expansion chambers but why can/should they not connect up to one muffler after the expansion chambers?
Because the timing would be off - it would be like 4 people trying to play the same trumpet but playing different songs
Are there any reed valve (or single way) type exhaust outlet designs?
Probably, I honestly do know. I'll let the horde answer that one........
so on this hypothetical seal for a hot and dirty environment. unless you can get a high temp flexible boot to work on a loose seal, seems to me that (if you don't need a muffler) you make that joint the final exaust port. the simple illustration would be pushing a tin can in and out of a very wide exaust pipe with enough gap to be equivalent to a normal exhaust
sir i want Yamaha rx100 cylinder block kit and piston kit can u suggest me who is selling
So what would happen if there were a hole in the expansion chamber? I have a yz125 with a ton of needle size holes from a shit weld repair job. Is it going fuck up the engine internally and decrease its longevity?
Nothing really, the pressure wave is too fast usually to even notice, but this depends on the size of the hole obviously
and why the trial 2 strokes bikes don't have a expansion chamber on the pipes??
How is it that 3 cylinder 2 strokes scavenge well with a simple exhaust? I read somewhere that the timing helps the exhaust pulses scavenge each other.
If each of your cylinders has a separate pipe, then it doesn't matter if you have a 1 or 2 or 6 cylinder engine - each cylinder scavenges on its own.
nice explanation. so if you have vario transmission- more or less the same high rpms that is no longer a problem? you just calculate your expantion chamber and thats it. or am i wrong?
Pretty much, the calculation will only get you so far, there some flow testing to be done, but once thats all done everything is gravy.
Seems like the expansion chamber makes the biggest difference in a two stroke exhaust, is there any benefit of an aftermarket silencer? Seeing as how they all are a perforated tube wrapped in fiberglass? (Speaking for dirt bikes)
Aftermarket USDF spark arrester silencers can add back pressure - vs- straight thru closed course motocross silencers.
Tunable exhaust is sort of a thing on two stroke jet skis albiet black magic. They have ECWI systems available that electronically inject some of the water from the engine cooling system into the exhaust stream before it diverges in the cone (since it takes water from the lake to cool we have an unlimited supply). Since the wave travels at the speed of sound people tune pipes by injecting extra water at low rpm to cool the pipe slowing the speed of sound down, lengthening the pipe. Tapering the flow back as the pump pressure and rpm increase with electronic solenoids and an MSD brain allows the pipe to heat up as the RPM increases speeding up the sound wave and shortening the effective pipe length. Can you go over some theory on how we could do the tuning better? Where should we be injecting the water in the pipe? Should it be in a fan pattern with a spray bar? Additionally how does a twin cylinder differ to a single cylinder in regards to using one shared pipe. We have an exhaust manifold that allows the cylinder gasses to converge before the expansion chamber, how would that affect the scavenging process? The engine that seems to be the most used in the two stroke circles on the stand up jet skis is a 62t yamaha twin cylinder 701 with a 81x68 bore/stroke. A video would be great on this premise if you have the time. Cheers.
is there anything like this implemented in a 4 stroke otto or diesel cycle?
Yes, most 4 stroke exhausts are designed to take advantage of exhaust pulsing, there will be a video on this soon - matt
I wonder if you could use a liquid seal from something like a sodium (well something more stable, but still point is a metal or alloy that melts at a certain temperature) and then having it wet the surface to form a thin film that acts as the seal. With the right viscosity it seems like the right kind of idea, the nice thing is that when it cools down it becomes a solid piece again so it won't leak on a low throttle setting.
Not a bad idea, given me something to think about - matt
i may have got this wrong ,it could have been ernst degner...give wikipedia a look.much info on early power valve development
When I was 16 I had an fs1e moped, the last of the non restricted ones. Will let people guess the year.. Anyway I cobbled together an expansion exhaust to try and beat my mate who had a Puch JPS. It never worked but I thought it created some kind of super vacum at the time. I pondered for ages how it worked and that was the best guess I could come up with. At 16 you know everything so was never gona ask anyone. Later in life I bought a KDX250 and it was only then I understood what they did and how they work... Some of the time.
why not use a spring loaded piston inside a sealed exhaust expansion chamber?
nice vid, although i more or less knew this, it's nice how understandable is your way of teaching, i have to give you that. one question though, and maybe you can address this in a future vid - how does the height of the exhaust port change how the pressure wave travels and what time does it arrive back at the piston. i've heard that the higher the exhaust port, the more rpm the engine will give. cheers - nick
Very good question and yes that is for another video - cheers for the great comment though - matt
Instead of changing the length of the whole expansion chamber, you could have a move-able internal baffle shaped like the convergent cone. You wouldn't need to worry too much about sealing the outer diameter of the cone, in fact you could leave enough clearance that leakage past the edge could be the flow path to your muffler.
moving it fast enough to keep up with acceleration in first gear might be a bit of an issue. A stepper motor and a threaded shaft maybe?
It's interesting how snowmobiles got around this problem, they use a CVT transmission that keeps the engine on the pipe instead of a pipe that adjusts to the engine.
like most mopeds. Great idea about an internal cone, the problem comes with having a motor that could survive the environment. As for the first gear problem and second for that matter, you could just ignore them. Have the cone at a set 1st and 2nd setting then move during higher gears where you need it most
i was wondering, does the end silencer itself also play a part in performance? alot of the older 2 stroke racers didnt have an end silencer, just the straight tailpipe. did they just come because of noise emissions or do they actually benefit the performance?
"i was wondering, does the end silencer itself also play a part in performance?"
- not really. The back and forth of the pressure in the expansion dampens any effect out.
thanks for answering, appreciate it man
No worries dude, that's what this channel thing is all about - matt
I have an exhaust with a second trail near the front of it, which goes to a reed valve, then through a tube to a filter thing that isn't hooked to anything. what is that?
EGR or some other emissions bollocks - Is it a 125?
@@dirtygarageguy it is a two-stroke so I think it is for scavenging
@@krazykracken1159 can you find the actual unit under its manufactures brand name trade name in the google images section of google search bar and if the ones of us who can draw an instant visual from just the. Written text as some i know can but i cant , show me the address of a pictured gallary namely google images from just one glance just mayne ill recognize it from some other...i gotvto govas my artificial intelligent trojan virus with pups is completely rewoeding every thing asvi typevfaster. That. I. Can. Correct and. It knows as i have. Our purposely. Agravatedvit. And it. Gets. More aggressive ...andvjust. the othwr day. This thing. Discover the program in a smartvphonev designed to antisipate your next. Wording became x rated and let me. Telll you if. How pleasant you become. Viewed. As i am now ..and. ill be. Damned this guy i barly know was rant about his phone thst was completinh. About. The same and thrn what hit us both like a ton of bricks our virus's are insulting ourv creditablity by using the exact wording that was a new attack use thevssme. Word we didnt disvover untill daysv later we just happen. To dicover so now wevknow that. Somsone. Is doing. This to us
@@donniebaker5984 What, really, what the hell was that
Hey man awesome video ty I truly enjoy and appreciate all of your vids I am new to 2 strokes so I have a quick question for you so does the length of the pipe before the expansion chamber matter because I took my pipe from another bike and had to cut a small section out but to be fair the whole thing wasnt very big and I may have removed about 50% please respond if you can ty for your time
Cheers dude
yea cheers bro but does the length of the pipe before the expansion chamber matter?
@@michaelhunter9485only part that doesn't matter so much is after the expansion chamber. Everything else matters alot in every dimension.
I still wouldn't go cutting any part of it without calculating and checking though.
So the point is to help with efficiency by forcing unburnt fuel/air mixture back into the combustion chamber?
yes but it is also a function of the system. If you remove the exhaust most 2 strokes can't maintain continual combustion. So its also an intergral part of the design in most cases.
At peak efficiency, it acts not only as a valve by creating equal or slightly greater back pressure in the returning wave, but after blocking the fresh charge from escaping, it'll leave a low pressure wave behind it helping pull the exhaust out after combustion. The best way to give you an example of pressure waves is with a wave machine or your hand in a pool of water. You'll watch the waves run out big and fast then bounce off the wall and return wider but about as fast. if you time it right, you can make the waves bigger without increasing energy. in a 2 stroke, any charge that leaks into the exhaust is actually a loss of charge volume making their less to compress meaning less power. Air has mass and inertia when traveling from the crankcase to the combustion chamber. Blocking the exhaust port or having trace amounts of exhaust re-enter won't stop the charge coming in but add more volume and act as a catalyst for combustion. Your car does this with the EGR valve to lower emissions. it does the same for 2- strokes also.
So, VERY complicated voodoo. But very very cool if you begin to understand it. Everything in a two - stroke is about timing. If you can time your high pressure wave to the low pressure wave on either side of the reed valve, you further increase efficiency.
Now, if you want to get really crazy, Husqvarna chainsaws have no......? Reed valve. How do you have a two stroke without a reed valve? Timing, fancy engineering, and probably more voodoo.
At peak efficiency, it acts not only as a valve by creating equal or slightly greater back pressure in the returning wave, but after blocking the fresh charge from escaping, it'll leave a low pressure wave behind it helping pull the exhaust out after combustion. The best way to give you an example of pressure waves is with a wave machine or your hand in a pool of water. You'll watch the waves run out big and fast then bounce off the wall and return wider but about as fast. if you time it right, you can make the waves bigger without increasing energy. in a 2 stroke, any charge that leaks into the exhaust is actually a loss of charge volume making their less to compress meaning less power. Air has mass and inertia when traveling from the crankcase to the combustion chamber. Blocking the exhaust port or having trace amounts of exhaust re-enter won't stop the charge coming in but add more volume and act as a catalyst for combustion. Your car does this with the EGR valve to lower emissions. it does the same for 2- strokes also.
So, VERY complicated voodoo. But very very cool if you begin to understand it. Everything in a two - stroke is about timing. If you can time your high pressure wave to the low pressure wave on either side of the reed valve, you further increase efficiency.
Now, if you want to get really crazy, Husqvarna chainsaws have no......? Reed valve. How do you have a two stroke without a reed valve? Timing, fancy engineering, and probably more voodoo.
The tuned expansion chamber is in effect, a supercharger, Cooling is the aim of having the exhaust port close just before the burnt products of combustion are forced back into the cylinder, where at high revs and lean mixture, they will raise the piston temperature above the accepted 550C that our race pistons could handle. Above this they would become "soft" and stick to the cylinder. (Nip or seize up).
What if instead of a separated sliding expansion chamber you used a sliding cone inside the expansion chamber that has a pipe that slides inside the outgoing exhaust. That would eliminate the need for a big seal along with the big pockets of disturbance. Maybe use a rack and pinion type system for adjusting the expansion via the sliding pipe inside the exit pipe, what are your thoughts? Thanks for another great vid
This will be in part 2, I'll take peoples comment and we'll go through what is and isn't a good idea and why - cheers - matt
LOL, just saw your very valid idea mentioned here. I have a post above about just this. :)
How 'bout a thin version of a cylinder with rings a larger cylinder as an expansion chamber. Would seal, but would add weight. Maybe a valve in the expansion chamber that opens an additional chamber?
how to 4 stoke pipe?
Do you get more low end power out of a bigger or smaller exhaust
What do you mean by smaller/bigger?
I mean longer or shorter
This is great and in no way trying to discredit the creator, I’m sure it was just a brain fart and he does know the right way but... the subject matter starting at 14:30 he has the explanation backwards. The explanation for the waves returning early is really for them returning late at that rpm range and vise versa for the other rpm range extreme.
Wow what would be the proper specs to let's say an 80cc 2 stroke and the exhaust size efficient for that motor? Or is there even 1 particularly?
And thanks for the great explanation
Each exhaust is designed for that particular engine
Ok so it dosnt matter if I put a kx 65 or a kx 85 pipe on the 80cc
At subsonic flow don't you normally get and increase in pressure in a divergent duct and a decrease in pressure in a convergent duct. Ie increase in velocity = decrease in pressure and decrease in velocity = increase in pressure? Bernoulli principle
Lee Harvey Griswold I'm thinking the same
could also use holes in the expansion chamber that open and close with valves, like the keys in a wind instrument. if you use a valve with variable aperture then you can get the same effect as a sliding exhaust chamber w/ a much simpler and more reliable mechanism.
Well it depends on what you wanna do. If you vent the expanding exhaust gas to atmosphere then that's no good.
yeah, I've not thought through the details. but since the basic task is to modify the frequency of the resonance, and we know that that is a way to do it, it's potentially workable.
I have a 1967 Yamaha 180cc twin 2-stroke street bike that's a project. This bike is a pre expansion era but I would like to squeeze more power out of the engine. How would you engineer the perfect pipe? :)
"How would you engineer the perfect pipe?"
- Perfect? Well it would have to be a variable expansion pipe.
I found some race specs online from 1968, where Yamaha made a racing version for close circuit. It has the dimensions for the expansion chamber but I don't know who could fabricate it for a reasonable cost. They posted other modifications to the motorcycle also, so I don't know if I would see good results by just doing the pipes.
Thank you for a great series!
I would like you to explain something for me: when i grew up i was the proud owner of a KX80 made 1986. I remember the absolutly monsterous effekt curve starting at about 9K revs. Resently i visited an old friend who bought a brand new for His kid. When taking it for a test drive there where almost no high rev hard on. I was expecting that. Why is there no "kick" in modern twostrokes?
The Workshop Hehe, i like your humor. When thinking of it many turbocharged cars from the eighties also had that kind of temper as well. For instance Volvo 740 turbo -85 tuned to about 300 hp had that kind of kick. Giving you a serious Hard on. I guess you are right that driving any vehicle with that kind of temperd engine takes some skill. Making engines that are easier to use are Good sales i guess. teoreticly, would it be possible to tune a two stroke that way with a 2 stroke?
To answer your question - modern bikes often have a powervalve which alters the exhaust port timing dependent on RPM, which smooths out the "kick" of the powerband and effectively widens the powerband out to lower RPMs so you don't feel the bike snap into the powerband at 8000 rpms, it more smoothly transitions between "off" and "on" the power at 3500-4000 instead.
I enjoy your videos, and am subbed..
But on this particular aspect of two strokes, (and porting) I've had a long acquaintance.. and feel you could have explained things better in different way... that most would understand immediately.
For instance, if you'd have used the analogy of sound propagation in air...
Sound travels in air in waves, as we all know.. and can be thought of as many waves travelling in concentric circles from the source, (at it's simplest)... And so, it's only a small step to show that the 'leading edge' of the travelling sound wave is the 'high pressure' part of the wave, banging up against normal atmospheric air... and the trailing edge of the sound wave is the lower pressure side..
Which is quite true.. and it can be shown to give a slight vacuum too as it moves along.
Just as tailgating a truck 'pulls' you along in the lower pressure envelope behind it.
And... just like a pulsing audio speaker beats the air to send it's pressure (sound) waves out...
Or... this analogy... concentric circles running across water from the splash... will 'reflect' (like sound will) off any solid, or firm, obstacle, like a boat or a riverbank, say.. these waves will reflect back towards the origin of the splash source if perpendicular to the wave, or glance off at the angle it meets the obstacle.
Similarly, the fat 'racing' expansion chamber will have a steeply reducing REAR cone (leading to the end pipe) in order to REFLECT a high(er) pressure wave back towards the exhaust port.
Personally, I think it's a bit of a mistake calling this a "rebound"... because a rebound implies that the exhaust gas actually travels backwards, and it doesn't.. (or.. only as much as a ball in calm water does.. when a wave passes by, i.e. it has a slight circular motion then returns to being still). The 'reflected' high pressure wave DOES travel backwards though... and the WAVE FRONT does a great job of putting a wall up against the next exhaust gas rushing straight out of the cylinder.. (But only at a particular and very narrow rev range as you mentioned).
The sound analogy is a bit more than an analogy too. Because the exhaust gas wave, the 'expansion' into the can, and the reflection back towards the exhaust port ARE sonic waves!
I just think that most folk will soon see the bunching up of the wave as it travels.. and the "rebound" effect... will be more easily understood if you mention sound waves.. Everyone understands a brick wall will reflect sound.. without even thinking about getting their head around molecules compressing together and then stretching apart...
Anyway, just my two penn'th.. and thinking out loud.
Keep the videos coming! :-)
Cool - and yes I agree. I'm not an expert in analogies and try to break it donw in a way I think works. This is not always the best way (obviously) and this wil be built on. As for trying to get across that exhaust gases don't reverse and its just the pressure that is reflect is also not entirely true.
Fresh charge escapes the cylinder and if the pipe is in its rev range then this charge is forced back into the cylinder. Now, I'm totally with you that the exhaust doesn't travel bak and forth but you can understand what I mean here.
The aim is to get the initial idea out, then build on it from there. But these comments are great, and will be added to the next video on this subject, which will have some physical deomnstrations
- matt
So does this mean with a rotary valve 2 stroke engine you don't need an expansion exhaust?
No because the exhaust port is the same - just a hole in the cylinder. The expanison pipe is basically an exhaust valve.
walter kaaden of mz invented the expansion pipe, to stop the profuse waste of fuel.the fact the pipe can be tuned was a bonus.
Say what? I'm sure it was the DKW designer Erich Wolf. Walter Kaaden was late to the party my friend. He picked up where Wolf had left off.
Hola. i,am argentina. don't understand you to much jajja, so, i thimk that's lovely explane. congratulations. your fonetic voice is very dificult for me. now, what about of resonance of exaut gas? is this one way of Arquimedes inverse efect? i surcribe you colega , greeting
He just speak English.
in regards to the problem of putting a variable expansion tube why wouldn't you just put a sleeve over the actual expansion tube feeding into the exhaust further back you don't need to worry about seals as much keep yourself thin and cheap underlay for a constant loss system if anyone will see this or understand me
Well done pal a good video, was half expecting an annoying yank trying to be funny. I enjoyed this .
Answered all my questions about a tuned exhaust... didn't even realize it was over 20 minutes, seemed like 5.
My bike doesn't have an expantion chamber. It never have. I have torn the exhaust apart, only thing I found was a mufflers system, which when I took out (for science) made it sound a lot meaner and gave it a bit more grunt as well.
More on this in as future video - matt
Looking forward to it.
I was thinking why not just have multiple expansion chambers?
Obviously for a 4 cylinder this would be impractical but for a single or a twin having a low mid and high powerband Chamber per cylinder seems like a good idea, only thing would be the branch and valve system to control the flow of the exhaust into these chambers.
This just seems too simple to have not been used though, but ive never heard anyone or seen any bike that even had a similar concept.
Of all the strange engines 2 strokes had tandem twins, square 4's etc this doesn't seem like a huge big brain complex one.
Is a flat baffle plate less efficient than a cone and why. Does some of the wave energy hitting a flat plate turn back to sound again or somehow lose energy? My 78 DT400 has a flat baffle plate, with a hole, installed in front of the convergent cone like a 2-stage baffle. I was thinking of removing that plate. Also, there is some fiberglass batting behind perforated metal screening along the belly section for sound deadening that I would have to believe might absorb some of the wave energy? Should I clean that out. Thanks again for the instructive video. Frank
This needs it own video, 1 - so other cna get the info and 2 - because I need to draw it out so its clear - great comment though - matt
Why doesn't this principal apply to 4stroke engines?
Because 4 strokes have an exhaust stroke, and in a way it does, but not for the same reasons - we'll be getting to this soon
Racing expansion chamber for go-kart have an adjustable Stinger slide in stop on the end of it so it won't fall off the end when you slide it all the way out if you change the expansion chamber size not going to run right cuz it has to be matched to the maximum flow of the ports
stinger length? Well that's not the expanison chamber is it?
@@dirtygarageguy forget about changing the expansion chamber size all you have to do is change the length of the stinger and it will change the frequency of the sound wave.. it's very easy to put a pipe over the Stinger ...by sliding the pipe in and out you change the torque ...its pretty easy to do as long as you have the engine mounted beside you as they do when you shorten your stinger you get more torque ..when you lengthen the the stinger you get more horse power and higher rpm
Simply put, it's because the two-stroke exhaust system, commonly referred to as an 'expansion chamber' uses pressure waves emanating from the combustion chamber to effectively supercharge your cylinder.as the boost ports are higher pressure the atmospheric pressure forcing against the combustion pressure that is still expanding this is what we call boost ..if it did not the intake charge will never make it to the combustion chamber as it has to be a higher pressure the the combustion ..when the piston compressed the air/fuel in the crankcase that started the boost above atmospheric pressure and as the piston travel picks up speed to the point its traveling fast enough.,,the air /fuel does not not have time to escape that is the exact moment the engine is self supercharging in the power band on the pipe ....simply put, it's because the two-stroke exhaust system, commonly referred to as an 'expansion chamber' uses pressure waves emanating from the combustion chamber to effectively supercharge your cylinder.
In reality, expansion chambers are built to harness sound waves (created in the combustion process) to first suck the cylinder clean of spent gasses--and in the process, drawing fresh air/gas mixture (known as 'charge') into the chamber itself--and then stuff all the charge back into the cylinder, filling it to greater pressures than could be achieved by simply venting the exhaust port into the open atmosphere. This phenomenon was first discovered in the 1950s by Walter Kaaden, who was working at the East German company MZ. Kaaden understood that there was power in the sound waves coming from the exhaust system, and opened up a whole new field in two-stroke theory and tuning
@@dirtygarageguy another thing another thing stop mocking me I haven't asked you if you got through diploma from a box of Cracker Jacks yet have I I spent a lot of years to learn this as I'm a retired tuner and racer many different teams that I've been on over the past 50 years doing this shit when I give you a reason why something works the way it does I'm not making this shit up is why I was trained by American Honda Suzuki Yamaha and Harley-Davidson I was going to Honda school when the first Elsinore 250 125 2 Strokes were born everything I've explained to you over the past few days came directly from Honda so if you want to fucking bitch about it you can see them motherfukers is in the one that tells us the way I'm telling you if you don't want to try engine's exhaust port can be thought of as a sound generator.
Each time the piston uncovers the exhaust port (which is cut into the side of the cylinder in two-strokes), the pulse of exhaust gases rushing out the port creates a positive pressure wave which radiates from the exhaust port. The sound will be be the same frequency as the engine is turning, that is, an engine turning at 8000 rpms generates an exhaust sound at 8000 rpms or 133 cycles a second--hence, an expansion chamber's total length is decided by the rpm the engine will reach, not displacement. Indeed, the only advantage to this crude pipe system was that it was easy to tune: You simply started with a long pipe and started cutting it off until the motor ran best at the engine speed you wanted.Of course those waves don't
learn and look at it and research it yourself I don't give a fuck before I ever attended any technical skills are various companies I spent four years at University of Illinois get a degree in applied science back in the late 70s in the late 80s my cousin Larry G Durkos was awarded a patent on the machine in front of you that's allowing you to read this ... I just a small drop in the bucket of accomplishments my family has acquired over the years not just working on kids toys
patents.justia.com/inventor/larry-g-durkos
"forget about changing the expansion chamber size all you have to do is change the length of the stinger and it will change the frequency of the sound wave.. "
- Very slightly - the main pressure wave is what does most of the 'work'
"when you lengthen the the stinger you get more horse power and higher rpm "
- I'm interested in how much?
"In reality, expansion chambers are built to harness sound waves (created in the combustion process) to first suck the cylinder clean of spent gasses--and in the process,"
- I get what you mean here, but your terminology is wrong, but the idea is ok.
"Simply put, it's because the two-stroke exhaust system, commonly referred to as an 'expansion chamber' uses pressure waves emanating from the combustion chamber to effectively supercharge your cylinder"
- this is completely wrong.
"as the boost ports are higher pressure the atmospheric pressure forcing against the combustion pressure that is still expanding this is what we call boost ."
- and now I see why. They were called boost ports because they're in addition to the standard ports 'boosting' (not like a turbo) - boosting as in adding.
"if it did not the intake charge will never make it to the combustion chamber as it has to be a higher pressure the the combustion ."
- If this was true, then how do non-expansion chamber 2 stroke engines work?
"another thing another thing stop mocking me"
- Well stop saying stupid things then...
" I've explained to you over the past few days came directly from Honda so if you want to fucking bitch about it you can see them motherfukers is in the one that tells us the way I'm telling you if you don't want to try engine's exhaust port can be thought of as a sound generator."
- Well that's a shame. The shame is that you didn't understand what you were being taught...
"Each time the piston uncovers the exhaust port (which is cut into the side of the cylinder in two-strokes), the pulse of exhaust gases rushing out the port creates a positive pressure wave which radiates from the exhaust port. The sound will be be the same frequency as the engine is turning, "
- The sound IS the pressure wave - jesus...
"an engine turning at 8000 rpms generates an exhaust sound at 8000 rpms or 133 cycles a second--hence"
- this is called Hertz (cycles per second)
"an expansion chamber's total length is decided by the rpm the engine will reach, not displacement"
- Well there's more to it than that. The exhaust length is determind by the heat of the exhaust gas (average) and the timing of the engine vs port opening time and finally the speed of sound of said gas at whatever pressure and density and temp is measured.
"learn and look at it and research it yourself "
- I was just about to say the same to you, but you need to.
"I ever attended any technical skills are various companies I spent four years at University of Illinois get a degree in applied science back in the late 70s in the late 80s "
- You need to give that degree back - or at least take the exams again.
@@dirtygarageguy i hunted for a long time today trying to find anything about the profession go-kart adjustable stinger expansion chambers as there plans to build them as they do exist here in indy where they were developed ..used by thousands ..and your saying changing the length of a tail pipe does not effect the tuning ..all you are suggesting me you have no experience are technical knowledge of the trade at all and didn't I tell you I'm only repeating what I was told at Honda are you telling me that Honda doesn't know what they're talking about? right they don't have a goddamn clue do they? Next you're going to tell me the Earth is flat right? Apparently you got your education like I said from box of Cracker Jacks as full of information as your Blackboard was the other day talking about exhaust pipes you haven't got a clue about as you have no facts the back anything you said that only because there is no facts you makes it up as you go along I watched you too many hour but you have a fine audience of millennials who would stick their head in a fire if I told them they would see hell . And your explanation of a pressure wave is bullshit it has nothing to do with molecules it has everything to do with sound frequency but you just us all Carnival acts have a carnival caller you're nothing but a snake oil salesman with a box of colored markers from the halls of the academe
Hiya... You obviously know what you're talking about ... whereas me... naaah! I'm in the process of, let's say, "refurbishing" a Honda Pantheon 125 (FES 125), which is the 2-stroke version from pre 2003 (it's a year 2000). It had been sat for 10 years outside, so there's a few things that are worse for wear on it, however, making good headway and surprisingly there are still some useful OEM parts available.
However, I'm looking to "beef it up" a bit and fit a Malossi Clutch set up and Final Drive gear for example, but I was also entertaining the idea of refitting a Polini Carb and Air Filter. I don't want to refit the original Honda exhaust back on it, though. For one, it's rusty as hell and yes I could clean it up and repaint it etc. but I wanted to fit a sports orientated or aftermarket exhaust to offer a little bit more power to the bike and to improve the aesthetics (the Honda exhaust is pretty ugly).
I've been all over the internet for 2 days looking for an aftermarket exhaust for it and can't find any manufacturer that has stock or even lists one! So, I've been contemplating, cutting off the Muffler from the OEM part and welding another 2-stroke exhaust unit to the pipe. It was that idea that brought me to UA-cam and obviously to your very informative video, which has now made me think that I could mess up the whole optimum output by doing that.
How much of an impact would it have, if I took a pot-luck shot at locating a random 2-stroke expansion and end can and fitted it to my scooter. What's the worst that could happen?
I would really appreciate your advice, thank you.
Curt
@The Workshop So canyon help or offer any advice please?
Bad idea to just randomly slap exahusts onto your engine and hope it works. If you have the time and patience, you can figure out your port timings, cylinder volume (125cc) and other factors and use a free pipe design software to calculate the most effective pipe design for your engine and desired peak power point and powerband width, and then measure diameters and lengths until you find something reasonably close.
Power valves change the torque. Example 250 Suzuki Quad two cycle had a manual power valve with three settings changed the size of the exhaust port from small equal the most torque to the biggest size give you most horse power
"Power valves change the torque."
- LOL oh here we go....
@@dirtygarageguy buy your self a two stroke 250 suzuki quad as it has a manual power valve with 3 settings closed give you the smallest exhaust exit equals more torque at lower rpms for narrow trails and steep hills with sort runs. the Third setting opens up the exhaust Port far as it will go for top speed hey babe babe Don this izuki wherever you said if that's where it's going to stay modern motocross bikes have a governor on the crankshaft and linkage rods for varying the exhaust port
engine's exhaust port can be thought of as a sound generator.
Each time the piston uncovers the exhaust port (which is cut into the side of the cylinder in two-strokes), the pulse of exhaust gases rushing out the port creates a positive pressure wave which radiates from the exhaust port. The sound will be be the same frequency as the engine is turning, that is, an engine turning at 8000 rpms generates an exhaust sound at 8000 rpms or 133 cycles a second--hence, an expansion chamber's total length is decided by the rpm the engine will reach,
At 17:40 I can hear the icecream van. Like a fruit boat please.