How 2-stroke exhaust pipes work | Offroad Engineered

[@StepstoPodium]

Thank you all for the love you have shown, I really appreciate it! 😊Note: No, I did not mention the first back pressure generated when the pressure wave reaches the divergent, which is responsible for creating some suction on the crankcase. I left that info out to make the video clean and simple (so everyone can understand it without being intimidating) and focus on the main pressure wave generated on the pipe!

[@Mr.WellingtonVonDukeIII]

Nah man you cool

[@Mr.WellingtonVonDukeIII]

Wtf

[@StepstoPodium]

@@Mr.WellingtonVonDukeIII I'm busting my ass out laughing with your comments, you're a legend! xD

[@richardkey4289]

Good explanation, people always wonder about 2 stroke pipe shapes. It must have been a freaky idea , whomever first considered it back in the day

[@StepstoPodium]

@@richardkey4289 Agree! 😂

[@DarekNiemczyk]

I didn’t know Zlatan Ibrahimovic knows 2 stroke engines. 😜

[@StepstoPodium]

Zlatan knows everything 😎

[@didik871]

Lol

[@Himal_Rulz]

At first glance i thought he looks like zalatan

[@Kartraceone]

Clearly he doesn't

[@maximilianklein9045]

@@StepstoPodium no no... Zlatan is knowledge

[@joshbroadbent9554]

team 2 stroke for life honestly

[@StepstoPodium]

👌😂😂💪😊

[@kirkthepimp1]

Im team both 2 stroke for wood and 4 stroke for track!!! If it’s got two wheels and knobs it’s a win for me ✊🏻

[@chriswebb383]

That seems backwards lol

[@huskyluva2180]

Chris Webb idk 2 strokes a much easier to ride through tight tracks and hills, just abit more clutch work, but that’s quite easy, on track 4 strokes rip

[@donniebaker5984]

@@huskyluva2180 four strokes rip because two strokes where ban from racing on tracks ...since the night at the indy mile when kenny roberts won the indy on a TZ750 two stroke inline four cylinder yamaha that in stock tune made well over 150 horsepower compared to all the four strokes barley make 100 horsepower ..it is impossible for the same size four stroke naturally aspirated engine you ever make more horsepower than a same size naturally aspirated 2 stroke that's why they were banned from MotoGP and the dirt track if you can't beat the competition get rid of it that is how we do it today

[@wilshirewarrior2783]

In early days the exhaust pipe was also referred to as an “ extractor” and the smaller pipe at the end was the “stinger”. M/Cs sometimes came with narrow stinger openings to get more horsepower but it caused the power to fall off at low rpm so commonly the stinger was widened in diameter to get power at lower rpm and prevent a bike from ‘falling off the pipe” or losing power. There were no silencers when I stated racing.

[@starwars615]

“It’s all about the length of the pipe” Facts

[@donniebaker5984]

There is no such thing as the legend of the pipe ..you have no facts at all and no concept of what an expansion chamber actually does as it it was explained to me by the team Honda Elsinore research and development program located in Milwaukee Wisconsin at American Honda training facility.. this was required by all Honda dealerships back in the seventies when Honda brought out the first of their two cycle Elsinore racing motorcycles as I was sent there by my dealership to learn all the technical aspects of 2 cycle Racing Engines

[@StepstoPodium]

Sure it isn't! 😂 Thanks for the comment though, I appreciate you letting us know your experience on the matter! It must have been a great experience that seminar Honda USA did! Great to see that even back then companies invested in those kinds of events for their employees 😊

[@goodbyemr.anderson5065]

donnie baker who are you taking to?

[@laurean5998]

In short: “According to some asians, it is not about the length of the pipe“

[@sethh1577]

“It’s actually the technique” lmao

[@thomasstark5381]

I ice raced Mercury sno twisters in the mid seventies and the pipes on those machines where never duplicated. Mercury even had Tipsters as modifications to enhance rpm. How to cut and shorten for a given rpm. Very high tech at the time. I believe it was Les Cahoun that developed those pipes. A talented 2 stroke engineer that ended up at OMC in their engineering room. A book called 2 stroke tunrs handbook was our bible in the racing days of design and mods. Cool stuff !

[@jacko4483]

Just subscribed and I am looking forward to digging into more of your videos! Turning 60 this year means nothing to me, I have four 2 strokes, two enduros and two trials, and I feel like I'm 40! But I have no problem learning from younger people and you clearly know what you are talking about! Thank you for your commitment to providing such good information! Blessings from Colorado!🙏

[@StepstoPodium]

Thank you so much for your comment and nice words!! I really appreciate it and I hope to see you around in thr comment section! 😃 Let me hear more about what you think about the videos 💪

[@powerwagon3731]

I’m turning 61, have multiple bikes including my new Beta 300 rr, from Colorado and feel 45 when I’m riding. Greetings from Buena Vista!

[@andretorben9995]

When I was a young bloke I rode in a club, one day this old guy turned up on a WR Husky. I thought "were gonna a be hanging around waiting for this guy to catch up", well stuff me, he rode the ass off me and most of the other guys.

[@salazam]

lol old people

[@donziperk]

Great to see you explain it so clearly. There is a mathematical formula for calculating length and shape of the pipe. I bought a book called The 2 Stroke Tuners Handbook 40 years ago and still use it. It has all the info for building pipes in it. I have built 3 and they all worked great. I checked Amazon that book is still available.

[@StepstoPodium]

thank you, I appreciate it 😊 maybe I'll get it! it's such a complex subject, it's never too much knowledge lying around 😆😂

[@sethbrown1763]

Thank you! That was really clear and made it simple to understand. I once built an exhaust pipe for my 2 stroke and it wasn't easy! There was a very good book on improving 2 stroke performance and the exhaust pipe was a huge part of that. Sadly, I lost that book somewhere along life. :(

[@StepstoPodium]

Im happy to hear that! I bet it wasn't but it sure was a good challenge, I imagine 💪

[@geoffreymandzuk5708]

Likely " the 2 stroke tuners handbook by Gordon Jennings"

[@33fastcar]

150+ psi, seal pipe on both ends. Torch the dents. If you have an air tight seal, the dents pop right out... Old dirt dog trick from the late 70's early 80's. If you do it right big dents can be repaired fairly easy. This really works! We did it on the worst of rainy days!

[@mirofin]

You need to fix it with ice

[@barryphillips7327]

A good explanation to the black art of two stroke exhaust pipes.

[@StepstoPodium]

Thank you for watching! 😊🙌

[@jessa813]

Thank you as a daughter who always annoyed her dad and brother with these questions this helped me understand why my kx 85 exhaust is shaped different from my klx 140

[@rcracer641]

When the 2 stroke is running, after the exhaust gas is pushed out, some of the fresh fuel air mixture gets into the exhaust pipe and that is what is pushed back into the motor to charge the cylinder with more pressure.

[@StepstoPodium]

exactly :)

[@NjoyMoney]

@Nimbus Nimbus Not really, the video kinda implied that the gas beeing pushed back is already combusted gas, there wasnt a mention of fresh mixture escaping the cylinder and that beeing pushed back. It might just be a language barrier thing :P

[@NjoyMoney]

@Nimbus Nimbus No he didnt? He didnt say it was fresh mixture that escaped the cylinder, he used the exact same icon for them as the icons for the exhaust. Implying its combusted gases that get pushed back in. Not my fault if you are not mechanically inclined

[@NjoyMoney]

@Nimbus Nimbus Its a smoke icon, explain why unburnt air and fuel would represented with a smoke icon? U are dense mate.

[@NjoyMoney]

@Nimbus Nimbus Also give me the timestamp where it says new air fuel mixture escapes the cylinder.

[@motorsrotors2127]

Very comprehensive video my guy. It's rare to find such high quality info, and graphics from such a small channel. Keep it up!

[@StepstoPodium]

Thank you so much! I really appreciate it! 😊💪 Next week I'm uploading a mega video about suspensions so don't forget to subscribe 😆😉

[@kingcosworth2643]

Another factor is the length of the divergent and convergent sections help broaden the usable rev range. as the convergent gradually contracts it is sending a positive sound wave back the whole time, weaker, but broader. This means it will reach the exhaust port over a wider rpm range, but it's peak wave pressure, and thus the engines comp ratio will be less than a more aggressive angled convergent section, same goes for the divergent section except reflecting a negative pulse for scavenging.

[@macattack9041]

It’s curved bc it can’t go straight. Got it bro.

[@williamnottbusch8024]

I use to race shifter karts and jet skis in my younger days. Temperature also affects the speed of the sonic wave. A rich or lean mixture will change the exhaust gas temperature and the tuning within the pipe. On our jet skis we would inject water into the pipe at various places and this would change the powerband due to the temperature change. We also used what were called center bleed pipes were the exhaust would exit out of the side of the cone. Didn’t affect power but made packaging easier. Lots of interesting theories on expansion chambers.

[@StepstoPodium]

Nice! Thanks for the info! It's amazing how specific the technologies can get in the various motorsports!

[@EarthSurferUSA]

Yep, the difference in the sound wave speed is because of differing exhaust gas temps, as the sound wave does travel a bit faster through hotter gasses. If your pipe and porting are tuned fairly well together, on normal pipes to me (not water injected), you can wrap the pipe with some pipe wrap insulation, for hotter gasses in the pipe and usually gain some top rpm.

[@-Maxim-90]

Wow, 15 years ago when i was riding a moped i told my father that a good exhaust is important for a 2 stroke,but i never knew why. He told me its better when the air just flew out without a pipe. Thats maybe truth for a 4 stroke. Now i know why its better with exhaust. Thanks for the good video, cheers.

[@StepstoPodium]

I'm glad I could bring some enlightenment after all these years! :P I really appreciate the comment, thank you! :)

[@makantahi3731]

no, 4s engine has bigger power with just good header(4-1) than without anything(engine masters)

[@fauzanramadhan9046]

It's really crazy to think, how just change the exhaust system can completely change both the power and the torque in the 2 stroke engine

[@michaelbrinks8089]

I figured the bulb part of the pipe would be closer to the exhaust port , instead of 1/2 way down the pipe.

[@BruceLee-xn3nn]

Not only 2 strokes and not only bikes

[@specialtymachining]

My Dad mentioned this to me back in the 1970's, but now I understand the dynamics. Thank you!

[@StepstoPodium]

I'm glad I could help! thank you for watching! 😊

[@JunkyardDigs]

Science 🤘

[@radowane101]

Biatche lol

[@H.EL-Othemany]

Fuck yeahh

[@gmx0413]

@@radowane101 ahhh you said it for me

[@aaron71]

Wow, thanks for such a clear explanation without taking forever to do it! Now I get why 2 strokes need back pressure whereas 4 strokes don't (or as much).

[@mowerdog]

It's not to increase the compression. It's to reclaim some of the raw fuel that escapes the cylinder during scavaging. CORRECTION. ... What I should have said was you can stuff " force " more air and fuel into the cylinder which can result in higher pressures and possibly more horsepower. However the compression ratio never changes.

[@StepstoPodium]

I understand what you mean by that, but it's a matter of perspective. If there was no expansion chamber, there would be no fuel escaping the cylinder due to scavenging (partly created by the expansion chamber) :)

[@MisterFurious71]

Which adds compression...

[@mareksumguy1887]

Steps to Podium I’m pretty sure a considerable portion of inlet charge (fresh fuel and air) would still be wasted out the exhaust port(s), even if there was no pipe.

[@StepstoPodium]

@@mareksumguy1887 Probably, yeah!

[@mowerdog]

I left out the word "ratio" on my first post which is my mistake. What I should have said was you can stuff "force" more air and/or fuel into the cylinder which can result in higher pressures and possibly more horsepower. However the compression ratio never changes.

[@MartyZaluski]

This is incredible info. I've been riding for 30 years, and just now learned why the power band comes on at a tight RPM range. Thank you!

[@StepstoPodium]

I'm glad I could help! I appreciate it 😁

[@TD402dd]

That is more commonly called an expansion chamber, but it also causes the power to have a narrower band. My friends used to say it was like a turbo charger coming on suddenly. For the average rider this can be very unnerving. For the others it gives a thrill to hold on tight and keep the front end down. My dirt bike had it, and my Yamaha RD400 had two, with the effect almost better than sex.

[@StepstoPodium]

"with the effect almost better than sex." - best way to finish any positive opinion about anything xD

[@APHEXSHAMAN]

Finally. KZbin content actually worth watching.

[@StepstoPodium]

thank you so much for that!!! 😀

[@MAsWorld1]

Excellent clear and detailed explanation!! I’ve been wondering how this worked for decades!! Thankyou👍🏻

[@impalaSS65]

Very complex subject, this explanation managed to at least touch on the major points. Most important being the fixed pipelength = fixed rpm peak or a trade off necessary - the graph showed it well. Well done! .

[@StepstoPodium]

thank you very much! I'm really glad you could appreciate the time and knowledge put into the video to explain it in a simple way 😉😀

[@darrelllatham6086]

And that "perfect" comp & rpm range is what we old guys refer to as "getting on the pipe". Nothing else like it. From 50cc to 500cc, 2 strokes can be a blast.

[@StepstoPodium]

amen to that!👌

[@AC-bl1rl]

HAHA!! I've nearly gotten friends in trouble in front of their parents for saying that. "oh yeah, we came around the corner and got on the pipe" or hit the pipe, and they thought we were smoking something. Just tires on the street, or roostin!

[@AnthonyLopez-dj4lf]

I’ve been wanting to know this for the longest time

[@mc1996]

Ah...a bela pronúncia portuguesa sobre o inglês :D Não engana! Não conhecia o canal, muito interessante.

[@StepstoPodium]

Obrigado! 😉

[@ruifreitas408]

Muito bom!!

[@StepstoPodium]

Muito obrigado Rui! 😊

[@ChocoFreak66600]

@@StepstoPodium Bem me parecia que eras tuga XD XD XD assim como o M Cunha não conhecia o canal... Big Props

[@StepstoPodium]

@@ChocoFreak66600 o que vem de Portugal tbm é muito bom 😆😂 grande abraço e muito obrigado! 😊

[@Tim542]

Whilst i ride them...ive never asked myself why they are shaped like that. Thanks!!! Very helpful and well explained.

[@StepstoPodium]

knowledge is power! 😆 Now you're going to look at your bike and question everything 😂😂 thank you so much! I really appreciate it 😊💪

[@moparone7962]

They're shaped that way so you have to buy a new pipe every time you smash a log.

[@StepstoPodium]

👌😂😂😂

[@lalilulelo1989]

heat gun + air compressor 😏 But make sure to secure the plugs and be careful. Slow and steady. Edit: Actually I might have used a torch. It was a long time ago!

[@JetSkiBuyFixPlaySellChannel]

They should use rave valves / power valves like jet skis. Then you wouldn't need the complex curves.

[@moparone7962]

@@lalilulelo1989 yeah, I do that sometimes. I wear my full riding gear when I do, had a plug shoot out at mach 3 before, haha.

[@Sanguine_Addiction]

Fantastic video! Definitely a must see for any two stroke enthusiast.

[@StepstoPodium]

Thank you so much! 😀 take a look at the suspension videos if you are interested in that topic as well 😁🙌

[@temp_uura]

Esse sotaque portugues nao engana ninguem ahahah. Subscrito! Adorei o conteúdo e a explicação direta ao assunto.

[@StepstoPodium]

💪💪💪

[@peterkang7640]

Great information bro! I just bought a used Goped gas scooter and it’s 2 stroke. I was thinking about making a rhino/snail shaped exhaust but didn’t know how it works. This helps!

[@saeednote7377]

gases when travel at speeds lower than sonic, their pressure increases when the cross section area of passway increases and their velocity decreases, and viceversa

[@neilpincus4667]

Correct. A bit of fresh mixture will end up in the header pipe but the return wave shoves it back in just before the port closes. The sound wave helps the pressure wave.

[@daytonwintle6051]

It’s opposite. You’re referring to the Venturi effect, when the cross sectional area increases, the velocity increases and the pressure decreases.

[@josepeixoto3384]

saeed note ---- what? you got it wrong?

[@Goldenfightinglink]

Jeez, hours of watching "fuel, air, spark" when it's "fuel, air, compression, spark". Never knew I needed a proper fit to get that back pressure, thank you!

[@faustin289]

Another reason: they look fricking cool!

[@c.a.marsupial.1282]

Excellent video. I'll subscribe. I owned the first Elsinore 125 back in the early seventies and now I know why it had such a beautiful big exhaust.

[@werdevo6]

Thank you for the good learn on 2 stroke exhaust systems!🙂

[@StepstoPodium]

thank you for watching and giving feedback! I appreciate it 😊

[@ANDREVDJMIKELI]

I think this must be the best video ever made to explain how it works or how to escape from a 2-stroke bike. Thanks !

[@StepstoPodium]

thank you so much for that! 😁😁💪

[@desertbrewcrew1974]

I actually learned something!! Like my taste in women, more compact and lots of curves. EXCELLENT

[@StepstoPodium]

I'm glad I could help! 😊 and damn good comment! 😂😂😂😂

[@CrossWindsPat]

First time I drove a banshee was a modded one and wow it was legit like a turbo. So much fun!

[@vitor26marques]

Parabéns pelo excelente trabalho que tens feito... Espero e desejo que o crescimento do canal seja proporcional à tua dedicação.... Um grande abraço...

[@StepstoPodium]

Um enorme obrigado Vítor 👐 é bom saber que quem vê os vídeos tem a noção do trabalho e dedicação por detrás dos vídeos 💪💪 grande abraço!

[@conrapal5408]

My gosh! how simple you make it! Congrats!

[@StepstoPodium]

Thank you so much! 💪💪💪

[@NjoyMoney]

2 strokes get so much extra power from a performance exhaust compared to stock, its crazy :D

[@StepstoPodium]

True indeed! 😁

[@tyroniousyrownshoolacez2347]

Zappa goes technical! Well done, thanks for sharing.

[@StepstoPodium]

Thank you for watching! 💪

[@wrestle259]

Walter Kaaden was responsible for the tech originally which came directly from the development of the V1 pulse jet flying bombs from WW2. Fascinating story

[@yordyiam]

The clever here is the way everything is explained. (Without falling asleep) 👌

[@StepstoPodium]

thank you soooo much! I really appreciate it 😀💪

[@Espinete87]

quick and interesting, thumbs up! i had a gasgas 250 enduro, and made dent, so... you answered a question that was in my mind almost 10 years XD

[@StepstoPodium]

thank you! I appreciate it! 😊 well, better late than never 😂

[@TomBartram-b1c]

Having watched several longer vids that left me none the wiser, finly crackled it. Thanks .. muito obrigadu!

[@StepstoPodium]

thank you for watching! I'm glad I could help! 😊😊

[@bruceparr1678]

Walter Kaaden, the man that invented the expansion chamber, said that when you get the perfect shape for the expansion chamber, it will not fit on the bike.

[@StepstoPodium]

😂😂😂😂

[@markwiley1538]

Bernoulli Principal is everywhere, great explanation! Thank you.

[@Luftbubblan]

Think i missed something in this video haha, ended up asking my self more questions. I learned something new today doe so tyvm for the video.

[@StepstoPodium]

more knowledge always leads to more questions, so you're on the right path 😉 thank you! 😊

[@donniebaker5984]

@@StepstoPodium almost cause you are close but not on the right path of the purpose for an expansion chamber ....its not about exhaust "back pressure" its all about the reflecting of sound waves traveling back to the exhaust port to seal in the boost pressure created in the crankcase ..the amount of fuel/air mixture you claim is being pushed back into the combustion chamber and to create higher compression has every little effect at all ...the higher compression was already created in the crankcase from naturally aspirated atmospheric pressure draft in the crankcase and then compressed by the Piston to higher than atmospheric pressure then transferred by the Boost Ports into the combustion chamber where it is compressed again before it is fired off

[@StepstoPodium]

Dude...... A sound wave IS a pressure wave. and no, the amount of boost that comes in through the reed valves isn't only from the crankcase, but also from suction created by a negative relative pressure created by the pipe (I explained on the pinned comment with I didn't include that part on the video). Look it up please.

[@markschlehr6911]

Very good explanation. Static compression is low but when running, the dynamic compression will be high due to the pipe pushing gases back into the cylinder. But it's not just exhaust gases, the intake charge will also start to escape out the cylinder into the pipe until the return wave pushes it back into the cylinder. Consequently, the volume of an expansion chamber increases the amount of intake charge that can be stored and pushed back into the cylinder.

[@StepstoPodium]

I appreciate it and thank you for the bit of extra information! 😊

[@vflinck1324]

Lets say i would ride a 2 stroke withouth a silencer would it lose lots of power

[@StepstoPodium]

silencer or expansion chamber? without the silencer it would do a loooot of noise. without the expansion chamber, it would do a lot of noise and lose a lot of power 😂😂

[@vflinck1324]

@@StepstoPodium so I've been thinking about a aprilia rs 125 stunt bike and i thought i could take off the silencer and put a db killer at the end of the expansion chamber so it wouldn't be so loud and this is because the silencer gets destroyed every time I fall

[@StepstoPodium]

@@vflinck1324 you will affect the performance of the pipe and the performance of the engine if you do that!

[@ginettaclark2387]

Depend, if the espansion chamber is designed to work whithout silencer, adding a silencer will reduce power

[@bonkeydollocks1879]

@@ginettaclark2387 all bikes have silencers after expansion chamber

[@HAL-1984]

Well explained and concise, your english is also excellent, better than many English people!

[@StepstoPodium]

Thank you so much! I really appreciate that! I take as a huge compliment! 😊😊😊💪💪

[@deborahchesser7375]

It’s hard to beat a light two stroke in the tight woods

[@StepstoPodium]

true that!! 👌

[@donniebaker5984]

Unless you are built like scott sumer was when he won the GNCC on a 1996 Honda XR600R that weigh over 300 pounds wet and when you kill it and crash you will kick it till you see stars before it will ever restart ...but ok scott didnt crash much at all , until one day he tried to battle it out with my friend's son who ran scott sumer off a cliff life lining scott to a hospital and costing team honda the GNCC championship for the year...the boy who did in sumer was Samson team rider and importer for TM off road dirt bikes

[@deborahchesser7375]

donnie baker I used to watch him muscle that hog around

[@deborahchesser7375]

donnie baker The TM’s, that’s cool, never in my price range, but an EC300 with those gorgeous blue rims? Oh yeh, I’d love to give that a home.

[@josepeixoto3384]

@@deborahchesser7375 miss that *a lot...*

[@jisooo-fx8sx]

Ive been looking for this kind of video. Finally my questions are answered, thank you bro your video is very informative!!

[@StepstoPodium]

Glad to hear that! Thank you for watching 🙌😄

[@charlesmanning5819]

Two strokes pips are called a tuned expansion chamber

[@intothevoid5027]

The YPVS really helped the RZ 350s get some low end torque, and with a set of good pipes and pistons and reed valves and head work you could fly.

[@copisetic1104]

Read prof Blair two stroke book. You have it partly wrong, when the exhaust wave hits the end of the primary pipe or header and hits the first diffuser there is a wave that returns to the exhaust port with a negative sign and helps extract more incoming charge thru the engine, it will pull a negative wave all the way back to the inlet port of the engine. In a well tuned engine I have seen negative and positive pressures over 7lbs and higher, the header length, diffuser and baffle cones will change the character of the engine. The tuning of the “stinger” will effect the temperature at the piston and effective rpm.

[@StepstoPodium]

I know I didnt explain every single detail about the difuser, it was meant to keep it simple and informative for about 90%. Sometimes if you go too much into detail, you loose the big picture, but I might do a video just for the 2 stroke! Nonetheless I really appreciate leaving a comment with your feedback, and surely everyone reading the comments do as well 😊😉 I will read it! thanks for that info! 😊

[@sergeykiz1728]

i was always very confused and curious how this pipe works and why it looks like this, thank you for explaining so simply!

[@StepstoPodium]

I really appreciate it! thank you for leaving a comment 😊

[@wawaron1407]

I learn...

[@agie170hss2]

To add a bit more detail to StepsToPodium’s explanations - I’ll offer a bit more information: A 2-stroke engine’s exhaust pipe can really be looked at as providing 2 different ways that it “functions”: one is sonic/acoustic, and the other is pressure/volume (look up “Helmholtz resonance” to learn more about the latter one). The shape of the divergent and convergent cones (that is: including angle, length, diameter) *primarily* determine the acoustic/sonic function of the exhaust pipe (and of course effect the total volume of the exhaust pipe). The “negative pressure” (as the sound wave from a single exhaust opening event travels down the exhaust pipe) is caused by the cross-sectional increase in area of the divergent cone. The angle of this cone, and its position relative to the piston face, are the primary considerations of the dimensions and design. Similarly, the convergent cone “reflects” that acoustic wave back in the opposite direction, and its shape/angle/length/position determine the timing/strength and duration of that reflected wave. Focusing almost entirely on the sonic/acoustic portion of the exhaust… what wasn’t mentioned, is that the port timing (position of the exhaust and transfer points relative to top dead center and each other) - typically measured in degrees - is the primary driver of the design of the exhaust pipe, at least when it comes to angles and lengths (there are other items I will ignore for now). For the moment, let’s assume that the crankshaft is rotating at a very stable rate (crank speed actually varies slightly *through* the stroke). For example, let’s say the engine is rotating at 6000 rpm. That’s 100 rotations per second or 10 milliseconds per turn. For sake of simplicity, let’s say the exhaust port in our imaginary engine opens at 90 degrees after TDC, and the transfer ports open at 120 degrees after TDC. Now we get to the interesting part - when the exhaust port opens, a sonic wave begins to travel down the exhaust pipe. The exhaust pipe could have a straight/consistent header diameter or have a slight taper. Regardless of its shape, we can look at the shape/angle/cross-section of the first portion of the exhaust pipe (from the flange on the cylinder, all the way to where the divergent cone reaches its maximum diameter) as being the portion that creates the “negative pressure wave” (primarily due to the increase in cross section). As that “wave” continues traveling down the exhaust pipe, it encounters the “convergent” cone, and as the cross section begins to decrease, a “reflection” reverses the direction of a good portion of that wave and sends it back toward the cylinder. In this very simplified example, we have 30 degrees of crank rotation from exhaust port opening to transfer port opening, and at least as importantly: 150 degrees of crank rotation from exhaust opening to transfer port closing, and 180 degrees crank rotation from exhaust opening to exhaust closing. So at 10 milliseconds for a full turn of the crank at 6000 rpm, we have .833 m/s from exhaust opening to transfer opening, 4.166 m/s from exhaust opening to transfer closing, and 5 milliseconds from exhaust opening to exhaust closing. These numbers ONLY apply at 6000 rpm, and this is a SUPER-simplified example. So, if we know the speed of sound (more on that in a minute), we can calculate “roughly” what the distance should be from the piston face to maybe the center of the rear/convergent cone, and back to the piston face for the convergent cone to be somewhat close to “in tune” (correct distance from the piston) at 6000 rpm. Many people have an idea that the speed of sound is around 750 mph or 1100 ft/sec, which holds true at around 70 degrees. Those numbers are way off for an exhaust pipe though, because the speed of sound increases dramatically with temperature. Of course the temperature varies in an exhaust pipe, constantly cooling as it expands and travels down the pipe. Let’s just throw a nice easy number at it, and say the mean exhaust temperature is 500 degrees F. Now the speed of sound is about 1520 ft/sec. Using the above numbers (once again: only as a rough example, simply to illustrate the concept), We have 5 milliseconds from exhaust opening to exhaust closing, and at 1520 ft/sec, that equals a distance of 7.6 feet. Of course we can divide that by 2 since the sound wave is traveling “out and back”, which gives us a distance of 3.6 feet from piston face to say… the middle of the convergent cone (and in reality, measuring a bit closer to the small end of the convergent cone may be more accurate). As can be seen, this is only one value, at one rpm, at one port timing, and at one mean exhaust temperature. A 2-stroke exhaust pipe has to be designed to work not only through a usable rpm range, but also “in concert” with other engine characteristics that go in and out of tune through the rpm range! It does no good at all to optimize an exhaust pipe for 6000 rpm if the port timing is far better suited to higher rpm, or of the volume of the crankcase works especially well in a certain rpm range, or if the intake length is tuned for a certain rpm, etc. etc. And… I have only been talking about lengths/distances and ONLY to the rear/convergent cone. (These comments don’t even touch on what happens in the header section and the divergent/front cone -- that could easily be another message as long or longer than this one.) Exhaust pipe volume, header diameter and length, stinger diameter and length, type/flow of silencer…. ALL those items add into the equation of building an exhaust pipe. Additionally, 2-stroke engines have many engine components and settings that go in and out of tune through the rpm range, and the exhaust pipe has to be designed to not only work best for a specific use, but work “in concert” with other setting and tuning parameters in the engine. None of the above even begins to discuss port timing or blowdown, ignition timing, combustion chamber shape and volume, roof angles of the ports, port “layout” (where each port is “aimed” within the cylinder), crankcase volume, tuned frequency of the intake tract and reed valves (assuming it’s a reed valve engine, which is the most common in 2-strokes), type of fuel, rpm range the engine will be run at, conditions/altitude where the engine will be run…. and many other items. Tuning a 2-stroke engine (or building an exhaust pipe for said engine) is an endless sequence of compromises. There is no “one perfect exhaust pipe”, nor is there any other “one perfect setting” for the items mentioned above. Many books have been written on exhaust pipe “theory”, and to be honest… the best tuners do a lot of cutting and welding and testing. The math simply does not always match up. Suffice to say that… 2-stroke exhaust pipe design is most definitely NOT a “precise science”!

[@StepstoPodium]

Thank you so much for the info and for not being a complete dick while addressing that (like many others have). I really appreciate the time you put into leaving this comment and thank you for complementing the info on the video! I wish more people were like you ! 😊

[@donniebaker5984]

Agie 170hss , all that and not one mention that two strokes are self supercharging making their own internal boost above atmospheric pressure producing much more horsepower per cubic inch at a compounding rate the faster it spins up ...

[@StepstoPodium]

@@donniebaker5984 Did you take that from Wikipedia? 😂Don't lie to me now 😉

[@agie170hss2]

@@donniebaker5984 Donnie, Crankcase pressure (what you refer to as “boost”) does not “compound” with rpm. There have been tests done on a variety of 2-cycle engines using ultra-high-speed pressure transducers in the crankcase, and while crankcase pressure absolutely *does* vary through the rpm range (and of course through each 360 degrees of crankcase rotation), it generally falls into the range of 0.7 bar to about 1.4 bar using an optimized tuned exhaust pipe. What crankcase compression does have is a “sweet spot” where the tuned frequency of the items that effect it (intake tract flow and inertia, crankcase tuned frequency, and of course exhaust pipe design) most closely are “in concert”. Air acts like a spring... and intake, crankcase and exhaust pipe all respond to the mass of the air and the spaces that contain it… no different than blowing into a bottle to create a tone. The “crankcase compression ratio” has finite limits as to what can be accomplished. Your explanation of how a 2-cycle engine functions is quite valid, up until about the mid-1970’s. This is when Morbidelli (an Italian furniture manufacturer that also built and raced GP motorcycles) discovered that a considerably larger-volume exhaust pipe of correct angles and proportions could draw much more air/fuel mixture into the exhaust pipe (and push it back into the cylinder with the reflected sonic wave) than could be accomplished with primary crankcase compression alone. This can be done because when the transfer ports are open, there is a direct connection from the exhaust pipe to the crankcase. (in other words, one could actually pull a string from the intake tract, through the crankcase, up the transfer passages and into the cylinder, out the exhaust port and into the exhaust pipe). Morbidelli was the first to "focus" on that period of time within the stroke that the transfer ports are open -- and *capitalize* on the connection between exhaust pipe and crankcase. Primary crankcase compression has finite limits - it not physically possible to make a very high crankcase compression ratio since there has to be “space” in the crankcase for the piston and rod to move, and also for a reed cage (as most modern 2-stroke engines use), as well as transfer passages and the space inside the piston. An interesting investigation into any 2-stroke engine is to “cc the volume” of the crankcase (fill it with fluid to accurately measure the volume) both at Top dead center and at Bottom dead center. What gets discovered very quickly is that primary (i.e. crankcase) compression ratio will only take an engine’s performance to a certain level. Morbidelli’s “discovery” of actually increasing crankcase volume (effectively *lowering* the crankcase compression ratio), but doing so in unison with the correct exhaust pipe design and intake/crankcase design… allowed a significant jump in performance. (Morbidelli dominated for a season or two as other manufacturers caught up). Very simply, what changed was that instead of using the exhaust pipe to “push back in” any air/fuel mixture that had “leaked out” of the exhaust port…… the new approach was to intentionally design the crankcase, porting, and exhaust pipe to “draw” much more air/fuel mixture into the cylinder *and* exhaust pipe than the primary crankcase compression ratio could “push” into the upper part off the cylinder. The focus shifted away from crankcase compression - TO crankcase and port flow plus larger-volume exhaust pipe design. - I should note that there was one exception to the “limitation” of primary/crankcase compression ratio: In the mid-70’s (as I recall), an Italian go-kart engine manufacturer built an engine with a “stepped” piston and bore. In other words: the piston displaced 100cc in the combustion chamber (as was within the rules), but the piston and bore were larger at the base of the piston. I don’t remember exactly how large it was, but as one could envision… this provided what was essentially a 100cc engine with a “crankcase pump” of something like 150cc. The engine was mechanically “clumsy”, and difficult to manufacture (not to mention having a very heavy piston). The idea was dropped fairly quickly and also banned in within the rules of kart racing. Obviously much has happened in 2-stroke design since the mid-70’s, however Morbidelli’s move away from relying on crankcase “pumping” is surely one of - if not THE - most significant changes in 2-stroke design over the last 50 years. The other very significant design change (IMO) has to do with the aiming of transfer ports, however this was more of an “evolution” over a number of years starting in the mid-90’s or so… and I would not consider this as important as what Morbidelli inspired. There have of course been other “tweaks” along the way, such as the “boost bottle” someone else mentioned (which is a method to shift the rpm of the “tuned frequency” of the crankcase). Fine tuning of intake tract, reed valves, port design, and exhaust pipe design have brought us to quite impressive performance levels over the years!

[@thejeepdoctor]

Hense the name expansion chamber. 😉

[@user-vp1sc7tt4m]

Expansion=cooling=reduction in pressure=minimize back pressure

[@fredgarvinMP]

I now fully understand what "on the pipe" means. Thank you!

[@StepstoPodium]

I'm glad I could help! thanks for watching! 😊

[@stevenleininger5682]

And I thought it was just to tell the difference between 2 and 4 strokes.

[@craigcp7455]

Thank you for teaching me my biggest passion!

[@Freaki91]

You missed something. Gnarly vs fatty maybe in a new video :)?

[@StepstoPodium]

in this video I didn't mean to compare specific brands/products, but yes, maybe for a next video! 😊

[@jaredalexander3403]

Yes that would be awesome

[@cprendon3]

Great visual and explanation of the body of the expansion chamber exhaust. There is one more part that has a major effect on the performance of the engine and that is the Stinger, length and diameter.

[@mr.houdini6701]

You look like Zlatan Ibrahimovic.

[@StepstoPodium]

I've been told 😂😂

[@mrgundersen3117]

A vegan zlatan....

[@StepstoPodium]

that, I haven't been told 😐😂

[@mrgundersen3117]

Don't feel bad... Zlatan is a big dude!

[@mrgundersen3117]

And I don't think there is such a thing as a two stroke lovning vegan.. 😀

[@charliecharliecharliecharl8554]

multi cylinder Two stroke exhaust systems are a work of art blending that power together

[@cyborg6008]

Dude thank you. I couldn’t this anywhere. Thanks for the great work and animation was super helpful!!!

[@StepstoPodium]

I'm really glad I could help! Thank you so much for the comment and for the good words 😀👌💪

[@socks2441]

if i have a few minor dents in the fat part of the pipe, along with some cracks. and i brazed them up badly with the oxy acetalene torch before it ran out of gas. still leaving a small leak. how much does this affect performance? the dents are still there, it still leaks a little. and adding that extra thickness to the metal etc does that affect the vibrations/ harmony of the pipe etc?

[@StepstoPodium]

it depends on how big the dents are. if they are relatively small, they won't affect much, but the leak is a lot more serious because that affects the pressure inside the pipe and will affect the pressure wave created to push the air fuel mixture back inside!

[@richardkey4289]

That leak will cause disruptions in exhaust flow, probably more than rouble than the dents; I have ridden bikes w,/ bad dents, but not super noticeable, however a,crack or leak causes pops, bangs, hiccups, throttle stuttering, ect. Get that shit fixed! Best wishes

[@justtim7334]

Back in the 60's my first bike was a 1957 Zudapp 250 Super Sabre.. It was a great machine. I sure wish I had it now.

[@thomasgorecki1321]

Great videos. Can you do a video on lubrication of the 2-stroke when there is the new direct fuel injection? How does the bottom end get oil in that case?

[@davidschmidt6013]

Great channel, just found it tonight. I used to ride a Yamaha 400 Enduro back home in the states. Now I live over here in Thailand where the bike drivers are COMPLETELY NUTS! I would like to get a little bike to putt around on but the situation here is too dangerous, now that I have a little one. But I enjoy your channel, and I'll watch more in the future. Keep up the great work!!

[@StepstoPodium]

Thank you so much for the kind words, I really appreciate it! 😊 Good luck there! Hopefully they don't get crazier than they already are 😅😅😂

[@wsmaga]

Very good information, I’m glad you included moped/scooter pipes.

[@StepstoPodium]

thanks! 😊

[@250txc]

Great! What about that ending cone area of the pipe as it tapers off into the stinger component, maybe the last 8-10" of the pipe ..

[@Gazanova85]

Best explanation by far 👌

[@TheBandit7613]

Thanks. How does exhaust shape affect the power valve? Another video in the making?

[@StepstoPodium]

Yeeeeeeessss

[@177SCmaro]

4 stroke headers work in a similar way but are more forgiving since they have an exhaust valve. If the reflected wave is timed right it can help pull exhaust gases out and even help to pull intake change in during valve overlap.

[@177SCmaro]

@@devilselbow At the collector, yes. I'm referring to at the exhaust port. At the collector the negative pressure "tail" of one pulse can help "pull" the positive pressure pulse of an adjoining cylinder if timed correctly. As you probably already know this is referred to as "scavaging". The intake side also benefits from pressure wave timing by helping to "push" more air into the cylinder and it's also why on "racing" cams there is so much overlap as it allows both the intake and exhaust system pulses to "talk to" each other but only in a certain rpm range. That's why they tend to have a rough idle. At low rpm with a lot of overlap you are creating a vacume leak when the intake and exhaust are both open on an intake stroke the piston is trying to pull from both intake and exhaust systems at the same time, which explains why engine vacume goes down with "big" cams. A lot going on.

[@ask_fornature4012]

Very interesting video, however I have one thought. How come the high pressure wave manage to push air and fuel mixture back in to the cylinder at the cylinder end of the diverging/converging pipe, but let exhaust gases through at the muffler end of the pipe?

[@tuomas2789]

Im not sure but try to imagine this. The exhaust gasses are flowing away from the engine the whole time, but but the pressure just increases within the gas and the pressure travels back up the bike. So no gas is going backwards and forwards its just the pressure. Not sure about that buy seems like it could be a reasonable answer

[@risdarputra9471]

Can you please explain the waving sound from the exhaust when the engine revved or during engine break?

[@mikeguitarification]

Great information, explained in a simple to understand manner. Thanks.

[@StepstoPodium]

Glad to hear that! Thank you! 💪🙌

[@ni3walia315]

Thank you I really appreciate it. will you tell me how to built own chember , measurements n all ?

[@StepstoPodium]

It depends a lot on the application 🙁

[@franktaylor7617]

There's a lot of tuning involved in building a chamber. Once it's set for a particular motor it's easier to replicate. My RG has 4 different chambers and the stinger (section before the silencer) length is different from one set to the other. All has to be taken into consideration during the build. This was an interesting and simple explanation of how the chambers work. 👍

[@StepstoPodium]

There is so much more to it than what I talked about, but for simplicity sake, I kept the maximum knowledge without making it to complicated for the average Joe to understand! There is thermodynamics to consider, resonance throughout the rev range, the valves, etc.., but that would be a lot more specific from each and every case. Thank you and I really appreciate the comment! :)

[@franktaylor7617]

@@StepstoPodium I agree. Exhaust valves, heat factor and so much more. I'm only good enough to be dangerous with a chamber build/modification.😁 It's really hard to explain to someone that has no idea what you're talking about. My coworkers eyes glaze over quickly when I start talking two strokes.😆

[@StepstoPodium]

@@franktaylor7617 I perfectly understand you! 😂 At least you can show them this video so they can look at you in a less alien like way 😆😂😂😂

[@richardkey4289]

Your bike has a crazy set of pipes.a buddy from school had an RG 500, Iit was a hi tech war machine! ( someone stole it at night downtown )

[@franktaylor7617]

@@richardkey4289 Thanks. They were Jolly Moto's. We modified them to fit the Honda chassis and swapped out the aluminum cans for carbons. It was a very low budget project but in spite if that, it came out really nice. I've changed very little from the original setup.

[@mrcolin001]

Finally... a gr8 explanation

[@StepstoPodium]

thank you! ❤

[@cmgray74]

Wonderful video! What would happen if you get hole in the pipe. Say a centimeter in size. Would bike have trouble running or starting?

[@StepstoPodium]

Thank you!! It would definitely have issues running and even starting, but it would depend a lot on where it would be as well

[@bwc153]

When there is a leak between the cylinder and exhaust pipe, where it's common to see a bit of oil seeping out of, is it also quite possible that this gap is in turn sucking air back into the engine too, leaning out the mixture then?

[@StepstoPodium]

Exactly! It just recently happened to me and I immediately noticed a decrease in performance

[@bwc153]

@@StepstoPodium Thanks for the response! I had been trying to troubleshoot my 2-stroke Paramotor's Moster 185 tendency to run lean even when the carb was set to richer than factory-recommended settings, and had initially ignored a small bit of oil seepage between the cylinder and pipe because other Moster 185 owners were saying "it's normal", definitely going to try and make sure mine stops seeping now!

[@christianfortadesembile5511]

Very clear explanations ! Keep up ! Greetings here from Philippines! 😊

[@StepstoPodium]

thank you so much! 😊

[@petrinimoraes]

Boa Diego ensina nos! - super enduro na veia! ae Diego estive pensando em criar tipo um "segundo estágio" ao longo do caminho dentro ou fora do escape ainda não decidi, o que vc acha que aconteceria, será que ia melhorar um pouco a eficiência da queima do combústivel reutilizado ?

[@alex-vc8lq]

finally i find video that expalins why twostroke engine exhaustpipe looks so weird. i neber kknow that before so thankyou. when i was young i dirive many different mopeds some have normal exhaus pipe and some have that kind of pipe you show us and we called them powerpipes and we do not even know why or how it gives more power 😄 some times i even think it.s give more power because it,s thicker than normal pipe althought the end of the pipe was not thicker at all and then we make power mufflers just taking out all things that are inside the muffler and and we think no we get more power although we get only more noise and maybe stupidest thing we do was to take whole exhaus pipe off and if im right like tthe motor makes less power and more noise and nothing else but we was kids and have mopeds so it,s almost have to try to tuning it faster. best tuning was change the chain gears that way we get the mopeds accelerate faster but stop speed got lover of course but it feels faster.

[@StepstoPodium]

Glad i could help! 💪💪

[@appleSUX1]

Thanks for the video. it was great. However, I have 1 question. Why is it necessary for the for the exhaust to go back and build pressure? Does it create more power, less power....what is the actual reason and would it do to the engine performance? Thank you

[@StepstoPodium]

Thanks! The goal is to supercharge the engine!

[@airgunbubba2505]

Thanks for answering the question of why that shape.

[@StepstoPodium]

it's a pleasure! Thank you for the comment, I appreciate it 😊

[@TommyNitro]

Simple and clear explanation. Thanks.

[@StepstoPodium]

Thank you Tommy! I appreciate it 👌🙌

[@golosbezdoka]

Hello, I'm translating motorcycle videos to Russian for my channel. May I take this one, I find it very useful, you're a great host as well? :)

[@StepstoPodium]

Hello! You can contribute for the captions/subtitles that KZbin provides 😊 if you download and upload on your KZbin channel, most likely KZbin will suspend your channel since its violating YTTS

[@golosbezdoka]

@@StepstoPodium I work with multiple channels and never had any issues. the only time it might happen is if you report the uploading manually as a copyright owner. That's why I'm asking you and if you accept it, you can simply send me an email where you're saying you don't mind I'm taking the content and if anything happens in future, I'll jsut show it and we both are great :)

[@StepstoPodium]

​@@golosbezdoka I appreciate the offer but KZbin already provides translations and captions for different languages! :)

[@Vyper5]

Hi, if you add the exhaust valves in the process how it works??

[@StepstoPodium]

The exhaust valves help the engine take the most out of the pressure wave. What happens is that the port valves open or close in order to give the pressure wave more time to be able to push the air fuel mixture back inside. I clearly will have to do another video explaining just the port valving so subscribe to not miss a thing! :)

[@Vyper5]

Thanks