Unlocking the secrets of 2 stroke expansion chamber exhausts E1
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- Опубликовано: 29 авг 2024
- This is the first video in a series looking at the science and mysteries of 2 stroke expansion chamber exhausts.
First we look at how the initial sonic compression wave is created during the blow down phase when the exhaust port just opens.
Then moving to the diffuser taper cone showing how the initial compression wave reflects a negative signed expansion wave back toward the cylinder to the open exhaust port to aid exhaust scavenging.
And then initial compression wave proceeds on at the local sonic velocity to the baffle cone taper and is then reflected back in the opposite direction toward the cylinder, meeting the exhaust port at the moment the pistons closes it to port plug escaping intake fuel air charge.
This video series will seek to explain exactly how those wave actions occur and the timing of them to match peak power output from a 2 stroke spark ignition engine thus unlocking huge gains in horsepower output..
Freeware 2 Stroke Expansion Chamber Exhaust calculator program
Download at birdcagesoft.com
(Page link on sidebar at site)
#2Stroke #ExpansionChamber
996 subs as I write with hours to go.
I can see the flag, we are looking at a Win.
Thank you to everyone who helped.
AuMechanic you got it hommie👍
AuMechanic Hey mate awesome stuff, do you have an email I can message you on to rack your brain on some more stuff? After some info on methanol and so on cheers
Fuck mate nice explanation... asking people for years why the exhaust chamber is always like this on a 2 stroke.. now I know
please,make subtitle indonesi
What is the normal/average compression on a 2 stroke engine?
Does it depend on the diameter of the piston?
Thank you
My dad recently bought a FMF pipe for his Beta 300. Gave a huge noticeable power change that made the bike scary to open when riding slow. Would wheelie up stuff like nothing. Then I got a project for school and I chose car exhaustes. Explained velocity and then I remember the expansion chamber on a 2 stroke
Very nice! Looking forward to the next episode!
Cheers.
When are u going to start ur new engine?
Good demo. Years ago I purchased a Suzuki Titan 500 twin 2-stroke. It came with mufflers that looked like logs. Swapped them out for some tuned expansion chamber exhaust and the difference was very noticeable. I'd bet better than a 10% gain.
Yes well tuned expansion chambers can result in some substantial power gains.
I want to see this series. I am always open to learning new things especially since I am about six decades old. I love expansion chambers and have a few for my little engines. I need to study theory more , as to get as much power out of my little motors. Cheers, R
I can relate to that, when I started road racing in the 80s I developed a bit of an obsession with expansion chambers.
And again in the 90s with sprint karts.
All I knew is that if a simple length of pipe could be responsible for so much power increase and capable of controlling characteristics of the the power curve, there must be something pretty amazing going on inside that tube.
Ill cover what I know about them but experience tells me there are things I do not know yet myself and may never.
Hello. I just came across your channel and im blown away with the kind of information you have put out to the world free to use, It's such an honour to be writing to you!
I run a small bicycle shop in Bombay India, and I have a two stroke bike the Yamaha RX135. I was sick of asking fabricators to help me build an expansion chamber that matches my cylinder ports. Im going to watch all your videos and make a tuned exhaust myself for my bike. And if im successful i will name the exhaust after you.
Much respect for sharing out such valuable knowledge 🙏
Love from Bombay.
Thank you for the comment.
I'm 6 years late coming into this thread, so bear with me please. I've always been interested in 2 cycle expansion chamber dynamics, and 2 cycle engines are having a renaissance at the moment, so here I am...
One of the points I picked up on (please correct me if I'm wrong) is that expansion chambers are more about sonic reflection than exhaust gas flow. Assumedly, the reflected return wave helps to prevent the intake charge from flowing out the exhaust port prematurely, and all this happens within the course of one revolution of the crankshaft. If I'm on the right track, then what keeps increasing engine rpm from overwhelming the completion of, and thus cancelling, this dynamic?
Thank you. belatedly, for sharing this information. And again, sorry I'm late to the party. Cheers!
This is by far the most informative and interesting video I've seen on RUclips in a long time, if only school would have been this interesting!
Thank you for the comment
Glad you found it interesting
If you have any questions feel free to ask
2-stroke is pretty simple but complex is well ,very clever explaining
Aye, Mate...I've a passion for 2 Strokes and particularly tuned exhaust systems. I am playing with several programs at present, and also doing the manual math and physics required for design.
Even Bell, Blair, and Jennings do not put enough meat out there to satisfy my appetite. Perhaps the reason being is we're using methanol/nitromethane as fuel. That really complicates the thermodynamics aspect, which in turn affects wave velocity.
Would be nice to chat with you sometime, as our backgrounds in the automotive realm are quite similar. I'm a retired design engineer from GM and specialized in zero phase concept development. Also a certified master auto tech.
Cheers, and thanks.
As you are likely aware there are 2 values you can adjust in Blairs equations to provide for different fuel types and air fuel ratios marked IGC (individual gas constant) and RSH (ratio of specific heats) which represent the chemical composition of the exhaust gasses that differ from air.
Many calculators Ive seen hard code ICG and RHS for air, I've left those values open in my Pipe calc software and the defaults I put in are for exhaust gas using petrol at an air fuel ratio of 13:1 so you can adjust those values to suit to reflect the exhaust gas composition which is used in the the wave speed equation and thus tuned length calculation. That said I'm not sure of the values you would use for Methanol NM mix. I know the RHS and IGC both increase with richer AFR.
Cheers.
I couldn't get my motorized bike up to operating temperature in the cold months, so I wrapped my expansion chamber with exhaust heat-wrap. Worked like a charm, but you can't use it in warm weather, you'll overheat in minutes.
Exhaust carries way a good deal of heat as does the large chamber from the barrel and head so wrapping it will store more heat.
Alternative in an water cooled engine is to just tape of part of the radiator.
Sent here by 2STROKE STUFFING, awesome technically detailed videos sir.
Hi Cole, thanks for dropping by to check out the videos.
More to come.
Cheers
Dave
Cool! Don't have time to watch right now, but I'll be back!
Let me know your thoughts on it.
So brilliant! Ingenious! I love 2 strokes!
Me too.
GREAT VIDEO MATE. you are right, I give the broad overview of how the pipe works but I am no expert on the subject by any means. RH DSD
Hi DIOSpeedDemon, thank's for the comment.
I started building them when I road raced 2 stroke twins in the 1980's, but it was hard to make a dollar doing it without computers.
Did a lot of research back then too, I'm sure you are familiar with Jennings work, 2 stroke tuners handbook.
But found other papers on the topic that are more detailed and as it turned out the Jennings book is more anecdotal than scientific and has one or two flaws in it.
So I'm going to do a series on it covering each part of the system in as much detail as I can from what I know and hopefully shine a little more light on how they work.
AuMechanic could you point out those flaws....maybe safe me a headache because you Jennings and Graham bell are all I learn from
I had no idea there was so much science behind a saw modification. Very interesting. Well put together, thanks.
Thank;s for the comment
Chainsaw mufflers are less complex in design but still have a formula used (provided by Prof Gordon Blair) to design them which I may cover some time.
@@AuMechanic chain saw engines are different than other 2 stroke engines, because they are run at one steady rpm, more 97% of the time vs up and down the rpm scale ..from Wyoming USA 🇺🇸 🤠
@@billallen4793 Sort of.
I use them often in my stump grinding business to lower stumps.
The saws run in an RPM range that is anything around the torque curve up to maximum RPM depending on the load present at the chain which varies a bit as you work the cut.
The reason they dont have an expansion chamber is mostly due to the fact there is not enough room for one on a general use saw (aside from competition saws), and emissions and such govt regulations.
There is however still a formula that applies to saw mufflers far less complex than an expansion chamber which can be broken down in its simplest form to having a muffler that has the largest practicable volume you can fit on the saw for best power and that "breathes" fairly freely even with a spark arrestor in place.
@@billallen4793 Also keep in mind that many 2 stroke scooters have CV transmissions that run the engine at even more narrow RPM than saws and they do run expansion chambers.
@@AuMechanic have you ever seen a rotary engine 2stroke with a expansion chamber exhaust? I've got a RE5 ROTARY ENGINE Suzuki 2stroke motorcycle 🏍 that I was building for the Bonneville salt 🧂 Flatts, but it ALL stopped in Sep of 2003, I became disabled in a workplace injury, so my projects were stopped then..from Wyoming USA 🇺🇸 🤠
Very good video. I never really understood how an expansion chamber worked. Thank you
Thank's for the comment.
This is the first "how an expansion chamber works" vid that I've watched that has explained what the diffuser does, most people only explain what the baffle cone does and when I tell them they are only giving half the story they just don't believe me!
This is exactly why I decided to start doing theses videos.
The amount of misinformation on the topic amazed me.
Even the Wiki pages on it are just wrong.
And check out the rest of the series as there is a bit more to the topic than just the cones too.
Walter Kaden of MZ of east Germany was the inventor, and father of the two stroke expansion chamber. Not a soul on earth had a clue before him.
So they say although Gordon Blair claims he saw chambers used by Montesa prior to MZ but we will never know and it doesn't really matter..
I think the first expansion exhurst was used on the v1 doodle bug in ww2
Hi Jason
Sorry but that was a pulse jet which has nothing to do with the principles of 2 stroke expansion chambers other than they look similar.
I stand corrected I've just descoved you're chanel I love anything to do with 2 stokes having various 2 stokes from 50cc up to 500cc motor cross bikes I think if you grow up round the 2 stokes it stays with you l don't think there is a better smell than Castrol r30 it takes you back.
Jason Peters ....ahhh yes....castor bean oil!!!
This was awesome - I’ve learnt so much
As the first wave reaches the expansion cone area it creates a vacuum behind it not a shock wave, as the primary shock wave expands. You can even tune a pipe so that it has harmonics of sympathetic resonance in which the primary shock wave is bounced off the closed piston to create extra negative pressure in the pipe for when exhaust port starts to open again. I've been able to carry this to the extreme of sucking the tops of a pistons off requiring detuning to keep things intact.
Its a compression wave not a shock wave, and it reflects an expansion wave that travels back up the pipe it does not create a vacuum behind the compression wave.
As you your piston top coming off, that is over revving and ring flutter (i have a video on also) possibly because the pipe was too short and allowed the engine to over rev.
The expansion wave from the pipe that aids scavenging is in the order of 2 times atmosphere and not even close to causing mechanical piston damage.
I believe (am sure) the sonic wave is not reversed until the wave hits the baffle cone, (tuned length measured a bit further than half way down the baffle cone from the piston face). The low pressure you are talking about (a vacuum) is happening where you describe the sonic wave, (because of the larger diameters of the diffuser cone and header pipe if tapered). Pipes were developed for 2-strokes, starting with a straight pipe. Than somebody figured if they cut the straight pipe to a better length, the suction, (as the gasses left the pipe into the atmosphere), could be tuned with the transfers opening for the first 2-stroke pipe scavenging. Then somebody put a megaphone on the pipe, and it made that vacuum last for a longer duration, widening the power curve. Then somebody put a baffle cone (reverse cone) on the pipe, and that is what harnessed the energy of the sonic wave for a supercharging effect.
Yes. I always understood that the reflection was from the convergent cone on the stinger end of the pipe.
You put it well m8.
Hi, yes you are correct on that. The expansion wave is a second copy of the initial compression wave, the compression wave continuing on to reflect off the baffler cone.
There are residual reflections of that which can super position with the primary waves making it difficult to read pressure time values of the primary compression and expansion waves.
This will be in one of the next few videos, it is covered loosely under resonance.
The expansion wave "shaping" is done by the angles of the diffuser which i cover in a later video in some detail that dictates the length of peak of the expansion wave.
The point of reflection is not so clear and Jennings and Bell papers on it don't agree with Blair.
Being that it reflects back upon itself as opposed to the diffuser that mirrors the compression wave might explain that.
Re the story on Walter Kaadan and MZ, there is a few version of that.
Blair claims he saw them on Monetesa pre dating Kaaden and MZ, not sure if we will ever know the whole history on them.
This video is basically the preface to the series that expands on each point in some detail, see the playlist or video list for the rest of them.
Cheers
Dave
+ rationalmartian
Yes that is the compression wave that travels down the full length and back.
The expansion (suction) wave is created by that initial compression wave as it passes through the diverging diffuser cone.
So then you have 2 waves, the suction wave returns early before Transfer ports close and the other pressure wave reflected back from the end baffle cone arrives as Exhaust is closing to stop intake charge spilling form the exhaust..
Chinese scooters with expansion chamber exhaust like this have a big fat baffle spot welded right in the critical area of the expansion chamber to deliberately restrict the exhaust to pass regulations.
This has to be removed by cutting exhaust open to get at it.
Once removed you will have a half decent exhaust system.
Norton and Triumph motorcycles used a reverse cone muffler which is of a tuned length for better exhaust flow.
They sound great as well!
G'day AuMechanic. You have done an awesome job! After doing a lot of research and several books and making several pipes I'm still interested to know more. This video made me think of things in yet another way so good on you! Subbed!
Glad to hear you find it interesting, and thanks for the sub.
Important thing to keep in mind to next video.
The sonic wave DOES actually get disturbed a bit by the gasflow.
You have different speeds of the pulse upstream and downstream :)
That's correct and well spotted, and not just flow direction either.
But we will get to that part I assure you, and more.
Next video is up and Ive covered this issue with wave speed variation with gas speed and how that relates to tuned lengths calculations making a return trip down and up the pipe..
And note that the sonic velocity does not change itself, its like a ripple wave in a flowing river, the acoustic velocity (the ripple) is separate from the gas velocity (the river) and very important to not conflate the two.
Hope that covers it.
Good 'o.
Just subbed too but you had already "passed the line".
I didn't realise it was you when I clicked. Then I recognised your Monika and picture from Matt's videos.
Thank's for the sub, every one counts.
Looks like it has gotten us over the line and I owe a big thanks to everyone who helped make that happen.
Saved from YT corporations new rules.
Cheers
Dave
Cheers from Canada. Great explanation,
subbed. You have the who's who of 2t in your comments.
Hi George
Thanks for the comment, and have a good New Year too.
Brilliant presentation, so easy to follow
Good explanations - looking at this the ultimate solution is an adjustable expansion chamber - I believe karters used to have something along those lines called a slippy (slipper) pipe - that does of course require straight sections at the various cone sections to even be possible, which is likely why it hasn't made it's way into bikes - one possible exception would be a reverse cylinder TZR as the pipe run is predominantly straight, or as straight as possible
There was variable pipes on old karts but it is possible they were regulated out of use in control classes and besides that running Caster the pipe would probably get gummed and maybe jam up so would need regular service..
Aside from that variable exhaust port has the same effect of changing the tuned length by changing the effective exhaust timing on which the tuned length is calculated, but also increases the trapped compression ratio at lower RPM so that pretty much made the concept of sliding chamber redundant.
Water injection is what jetski 2strokes use to adjust volume in the pipe.not ideal for road racing.
At last I have found some good and understandable for myself should I say information on how to design your expansion chamber.
What a fantastic vid. I finally begin to understand this. Thanks for explaining it so well....
Thank's for the comment
do you get into the math of designing them? super keen to start designing pipes for the 50cc scooters
Yes I cover that in the designing chamber series.
There are a number of vidoes covering the equations in a playlist.
ruclips.net/p/PLIxC_wjJqk0rYVOG6EpLU2EaAVWZ2saWA
Reliability goes down with any expanded 2 stroke,just so you know.
hmmm, I read about making the ports larger. to me just take the steps and make a mirror shine. don't make them bigger, just the casting. its bumpy and restricting, all about flow. your chamber sound wave reverses and tries to hold in the next charge.
Ill be doing some more on this topic later.
Thank you so much! This was always a mystery to me, but you explained it very well.
Thank you for the comment
Great videos. I am riding a dirtbike in the snow (ski/track) and am thinking about about ceramic coating or wrapping the pipe with fiberglass wrap. This will help keep heat in the pipe on cold days so the scavenging / port plugging will be happening in the intended rpm range?
Can you clarify this for me if the pipe temp is colder than usual then properly timed scavenging / port plugging will happen at a lower rpm and if the pipe temp is higher than normal then properly timed scavenging / port plugging will happen at a higher rpm?
Hi James
The higher the temperature is the faster the sonic velocity is and so the faster compression wave will travel which will favor higher engine RPM.
So keep in mind that off the peak as the pipe cools this will favor lower RPM range which can benefit power at lower speeds in tight sections.
There has been some Kart pipes and days past that actually had water injection to cool the pipe down in tight sections of the track (not legal under moderns regs)
can you do a video explaining double charging the cylinder using the exhaust
Interesting to learn the theory why there is an expansion camber. One thing - youre text hides the drawing you are explaning......
Excellent video! Every bit as erudite and helpful to me as the A.G. Bell classic I have been studying as often as possible.
Great video!!! I've been trying to work out a pipe with a broader tune band!
Thanks for the comment.
Thank you I have a BSA BATAM 175 B ENGINE can you disgust a system.? Thanks you .David uk
Hi David
What do you need to know ?
You can email me, see Email address in "about" section of the channel
the headers on 2 stroke dirtbikes now the way they are all tapered out right from the cylinder, is this causing a negative return wave right away as the ex port cracks the sonic wave into it, or is this just to allow a steeper angle where the diffuser starts its divergence from the header so there's not the sharp turbulence where it transitions? I dont think a light negative return wave would hurt anyway right at ex port opening?
Good question
The taper angle of the header is not sufficient to generate an expansion wave, there needs to be an increase up of angle in the order of 7 or so degree or a sudden stepped increase in pipe diameter.
The taper of the header reduces the sudden change of angle at the diffuser but also helps focus the returning compression wave (for port plugging) according to Blair.
@@AuMechanic great thank you, that makes sense. A lot of people using old MX 80cc expansion pipes for their gas bikes, those pipes are made for a geared bike so I think they would benefit from some adjustments like extending the header to get the baffle farther away to lower rpm range that it works. And I wonder why they never have much of a natural chamber compares to a moped pipe ...anyway the group has almost 5000 members now, I'm always directing them to your videos, all great stuff. You should join, zeda mafia has bicycle group on Facebook, you could peek at the pipes being built maybe add some input and in turn gain a bunch of viewers, had to suggest it, would love to hear some of your input on what these guys are doing, great welding work but not so much knowledge of what to tweak where
Thanks for the shares
ll check it out
The main thing with the chambers they are using is they should at least calculate the tuned length Vs the RPM range of the engine they are used on to be sure that is right, there is videos here that provide the equations to use
ruclips.net/p/PLIxC_wjJqk0rYVOG6EpLU2EaAVWZ2saWA
Second thing is the ensure the header has a clean entry to the chamber where they weld it on and no large step at the entry that will upset the returning waves back to the port..
Absolutely brilliant stuff mate!!! Explained perfectly and clearly!! Subbed and liked mate cheers!!!
Cheers Jimbo
obviously we have sound waves making it out the stinger. is this the wave returning from the combustion chamber? or "Extra waves"?
The sound coming from the outlet pipe will be the residual of any compression wave that is reflected but mostly the initial compression wave.
By having the outlet pipe inserted back into the chamber or to the side can reduce the sharp peak of the sound out of the outlet pipe without any loss.
I cover a bit more about the outlet pipe in a later video as well as the build series with equations where I cover how the length of the outlet pipe is not critical and in fact so long as the initial diameter of it fits the outlet ratio equation the rest of it can be larger and shorter
Why doesn't the explosion (fire/heat energy and high pressure) ignite the incoming air/fuel mix? Why doesn't the fire get forced into the crankcase that's currently under increasing pressure full of boom juice?
Because the exhaust and transfer ports are closed or covered by the piston during combustion when it is still near the top after it passes top of the cylinder and begins the downward stroke..
Once that is complete and the piston moves downward the exhaust port is the first to open, when it does most of the pressure is released to the exhaust before the transfer opens, that is called the blow down stage, as the piston continues to go down the transfers open next, at first some exhaust gas flows backward down the transfer but as the piston continues to go down the pressure in crank case is rising and the exhaust being open the cylinder pressure continues to drop at which point intake from the crank case flows upward into the cylinder.
@@AuMechanic I understand the principles of what is supposed to be happening. The compressed air/fuel mix is detonated by static electricity jumping from the negative electrode to the positive positive. Some of the matter is converted to heat energy in the form of an explosion. The cylinder dome and walls contain this violent release of energy which allows the piston to convert it to mechanical energy. My problem is the piston hasn't converted all of it. There's plenty left by the time the exhaust port opens, which is necessary, but the intake port opens and new air/fuel mix is being forced into fire that hasn't been completely expelled. It didn't have enough time. Even when the piston reaches B. D. C. and all the usable energy the rotation of the crankshaft will allow has been transferred, there's still fire waiting in line at the exhaust port when the cylinder gets flooded with some easily excitable molecules. The way I see it, if there isn't enough explosive force left to push into the intake, then the new comers to the cylinder should at least burst into flames, chain reaction through the intake and consuming all the air/fuel hanging out in the crankcase because the Reed valve couldn't stop them forcing themselves in there but stopped them cold when they tried to go back.
@@cliffcampbell8827
Firstly to clear up a few points there.
The spark is not static electricity, it is generated by induction in the ignition coil.
Combustion is not an explosion it is a rapid burn of fuel
It is not contained by cylinder walls at all it is contained by the cylinder head, specifically the small combustion chamber dome of the head, the surrounding area of which is called the squish band is to limit combustion to the centre and stop it occurring at the outer regions of the cylinder head.
Second part.
By the time the exhaust port has opened combustion is long completed and there is no "fire" left only the residual exhaust after combustion.
In addition to the fact that there is insufficient pressure remaining in the cylinder to support combustion even if there was a spark.
Note in some twin 2 stroke engines that have a dead spark system a spark occurs when one piston is at BDC and no combustion occurs because there is no compression.
@@AuMechanic I took a small engine class for 1 semester way back in high school. I think that I am not remembering everything from those lessons correctly. I do remember something about flywheel magnitos and after voltage goes through a coil, 6 v becomes something like 40,000 v. Electricity, if it is or isn't static, household or auto, none of my business, but I do care about very much about avoiding electricity. We don't work welI together so if I don't bother it then it (usually) doesn't bother me. Filth washes off. Most cuts and scrapes I get are patched with masking tape, but I categorically refuse to dance with amps. It only knows the rigid-twitching two step and it likes to lead.
@@cliffcampbell8827
Yeah I'm not too keen on getting zapped and in later years with modern ignitions getting zapped by a plug lead is particularly painful.
I've got a few earlier videos on how ignition systems and such work.
Thanks! Very nicely done. Two strokes are the best. May they be with us forever. What do you ride usually?
Thank's for the comment.
Used to road race 2 stroke twins in the 1980s, that's when I started building 2 stroke race chambers.
Raced 1000 cc super bikes for a few seasons. (image in the channel banner)
Got into Sprint Karting in the 90s a bit and a MX 2t in my teens and later.
Been thinking about doing a bit of Karting again.
Whats your preference for 2 strokes ?
2 strokes are amazing machines, why do some racing pipes have a smaller diameter stinger at the out let pipe? Does this increase rpm’s? And how about the difference in length on the expansion chamber? Thanks yr videos are really interesting
Hi Brian
Ive got another video in the series that covers the outlet pipes and tuned length of the entire chamber, as well as the latest video on pipe software that covers more about outlet pipe size.
AuMechanic thank you
Thanks for an awesome explanation mate
So do expansion chambers require back pressure to function correctly (Eg, a smaller diameter exhaust outlet compared to the size of the exhaust port after the expansion chamber)? I'm not sure if back pressure is even the right term so I apologize in advance if my terminology is incorrect.
Hi Fridgemusa, in short yes back pressure does play a part as RPM rises to peak as it increasingly has a port plugging effect in addition to the reflected compression wave off the baffle cone.
I've covered more in episode 7 and elsewhere in the series, check the playlist you'll find it there.
Back pressure is simply a result of a restriction in a pipe so it is the correct terms to use.
Cheers mate :)
I would like to see the presentation on tuned chambers and outlet.....where are they?
Hi Ken
Re "presentation"
Are you referring to the reference material used in the videos ?
Yes, and I did fund it.
I am a competitive model speed flyer and most classes have banned use of a tuned pipe, but not all.
I.m particularly interested in the stinger and what it actually does. My general take is the larger volume the pipe, the smaller dia and or length of the stinger. Trial and error has been my best instructor. I have 4 records and looking for another if I can get the pipe sorted out.
Thanks
Ken
@@kenburdick5976
My videos are mostly based on the works of Gordon P Blair Professor of Mech Eng of Queens University Belfast from his book published by SAE in 1996 called "Design and Simulation of Two Stroke Engines", it is very complex and long so my videos basically boil it down in to a simpler form, also based on my own experience building chambers for road racing which began in the 1980's uses Gordon Jennings "2 Stroke Tuners Handbook"
Later in the video series I also discuss an article on outlet pipes called "Effect of Tail Pipe Entry Geometry on a Two-Stroke Engines Performance Prediction", published Dec 2000 by Cornelius Gysbert Johannes van Niekerk, Master of Engineering at Dept of Mechanical Engineering and Aeronautical Engineering Pretoria University.
Just found your channel and I’m very excited to watch your series on designing a tuned exhaust. I’m in physics and I write software for numerics, simulations and such, but all I know how to do for this problem is write a solver for Navier Stokes, which is very difficult, complex, and computationally intensive, so I’m interested to see what simplifications are allowed to reasonably model an exhaust system.
The videos on Expansion chambers is based on the publications of Prof Gordon Blair.
You might like to read his book "Design and Simulation of TWO-STROKE ENGINES" published around 1996 which are the basis of SAE papers he published.
He has an earlier version around 1990 but there is some changes in the 1996 version
When I started making expansion chambers in the 1980's we only had Gordon Jennings "Two Stroke Tuners Handbook" to work form which are fairly simplified.
Thanks for the references!
@@AuMechanic if you change the length of the header before expansion like shorten or lengthen does this have an effect on the timing
@@davidbroomhall7321 Since tuned length is calculated from the port window to the end of the baffle cone, changing the lengths of any part therein will effect tuned length.
I suspect what you are referring to is the "Jennings" pipe equation created in the late 1970's that provides a max and min lengths of header and the result of changing it, but be aware his equation was created by measuring race pipes with some observations and not by any scientific methodology as with the "Blair" equations that were created in the late 1990's I use in the software and in the videos series.
I have a 2stroke tipple 1000cc sled.Exhaust is in really bad shape so I'm installing 3 cherry bomb glass packs for expansion chambers and fabricating same as stock inlet diameter pipe and same diameter as stock exit pipe after expansion chambers. Will still have stock silencer. Thinking this will keep me in the ballpark for factory back pressure.
That would significantly reduce the power of the sled.
Back pressure is only one factor of the expansion chambers performance, the rest of the video series covers what the other parts of the expansion chamber does.
You would be much better off repairing or replacing the stock chambers.
Can you define "really bad shape", what sort of damage do they have.
Is there some type of formula where you would use the speed of sound related to rpm and distance of stroke and port height with the sound wave that would give you a desired pipe length for a desire powerband?
Yes there is, I've provided all the equations in the latest 4 videos to measure those values and calculate tuned length and port area for designing a tuned expansion chamber.
AuMechanic how up to date is that formula ur talking about?
thanks for explaining
Thank you for the comment
You said the negative sonic wave doesn’t care about the exhaust gases because it’s a sound.
So how does the positive sonic wave help retain the intake gases?
They key to this is that the wave is only providing a localised change of the gas pressure at the point to wave is. And by way of the pipe length dimension is timed to arrive at certain points in relation to the ports closing.
In the case of the compression wave reflected, it does not push the gas back. It simply raises the gas pressure at the pipe side of the exhaust port, if timed to arrive correctly, just before the port closes, that reduces the pressure differential each side of the port suffice to reduce intake mixture spilling out of the exhaust port.
I cover this more in ensuing videos.
Very informative video
Glad you found it useful
@@AuMechanic very useful i'm currently doing some research on the gordon jenning and blairs equation.. I'm currently trying to understand and determine what the correct size of tuned pipe base on the exhaust port.. Still have tons of questions need to get answered 😅
@@no0batwork157
I've got many videos on the topic here that cover about any question you might have, I also wrote some windows freeware calculator using Blairs 1996 equations too that there is a few videos on here.
Any questions feel free to ask.
@@AuMechanic thank you sir.. I'm looking forward to review all you video..
Again, thanks for another very informative video, Question: I just bought a kx80cc exspansion chamber for my motorized bicycle and i dont have the header flange can or should i weld it up on the 40mm head flange or do i have to use the spring method? Im thinking itll be okay as long as its bolted up well at 3 points. Am i wrong or right? I dont have that little part that the pipe slips over at the head im going to make one, do i use springs or can i weld it up?
Having spring hooks is not crucial, it just helps isolate the vibration of the pipe and engine.
If you are going to fit it to a different engine at min
Also, if you are going to fit a chamber to an engine it does not belong to at minimum ensure the tuned length of it is right for your engine otherwise the operating RPM range of the pipe you have could be way out of the ball park of the RPM range you engine produces power at, in which case the pipe will be less than useless and may even result in less power than a stock muffler.
See the video series I've done on How to Design an Expansion chamber, that gives you the sums you can do to calculate tuned length of your engines exhaust to match the pipe you are fitting to it with.
AuMechanic thank you i will check out that video. I think im going to just weld it up to the exhaust flange.and refrain from dropping it hahaha! If it had springs drop wouldnt hurt it but if its welded it may crack somewhere not good.😉
I can’t wait until I can actually build my first correct pipe… I couldn’t help myself and grabbed a little cheap banana bike engine pipe from eBay just to being to play with… it’s not really got the correct degree angles so it’s pluses will be correct but I just wanted to see if I could get something more from my engine… I’ve got a couple of the echo chainsaw actually fire rescue saw’s were y first two that I got from the fire house for doing some great work as a volunteer when they went the I found a cs8000 instead of the QV 8000’s that I’d gotten from the firehouse… and it’s just very interesting to see how that echo factory “ported “ the rescue engine for more power than their regular saw cylinder… cutting the squish band to reduce the combustion chamber… and some small changes to the intake and exhaust port window’s… I’ve actually always wanted to pipe one of those QV engines as they have a quite rounded shape to their exhaust port window’s compared to a regular rectangular saw engine… theses resonating sound waves helping to control your engine similar to a valve system has just always been extremely interesting to me…. So it’s so exciting to see that in a little bit of time and studying I’ll be able to cut my sheet metal and weld everything together… what gauge metal is a good starting point as it’s been some time since I’ve done any welding so I’m interested in grabbing some sheet of the correct thickness just so I can start practicing with making some cone’s and rings for practice…???
Hi David
Re sheet metal thickness, about 1mm thick is a safe bet as it allows some leeway with welding.
love this explanationm keep it up!
Okay... I have a couple questions...
When figuring which expansion chamber you need for an engine, should you base it off of CC to internal pipe diameter nearest piston; CC to internal pipe diameter at exhaust exit; or CC to area inside chamber? (and what is the appropriate ratio?)
I’m wanting to fit an expansion chamber to one of my chainsaws that I abuse with occasional milling work, and then if I like the results enough may make the addition to all of my saws.
Hi Rick
Not it is not only linked to CC there is more to it..
It is link to CC in so much as it is a ratio based on the port size and a larger engine will have a larger port size but the exact ratio is based on the expected pressures in the pipe which is based on BMEP.
There is a video playlist with a series in it covering all the equations required to design an expansion chamber, you will find the answer there to calculating the mid section. and exit pipe diameter ratios with explanations..
I will have a freeware downloadable pipe calculator software available soon that puts all the equations and ratios into a software to do quick calculations.
I was just reminded I someone let me recommend the two-stroke tuners handbook.
That was written by Gordon Jennings in the 1970's and is a bit dated, more recent books published by Professor Gordon Blair in 1996 but its is far more technical then Gordon Jennings 2 Stroke Tuner Handbook.
Hi thank you for that you are the only one that has given that but how long is a tuned lengh be for the muffler and wether from the start of the exhaust at the head if it has a bend in it will some of the exhaust gases bounce back causeing power restrictions pls let me know
The tuned length is taken from the port at the cylinder to the exit of the reverse facing baffle cone taper on the expansion chamber for Gordon Blairs expansion chamber formula which is what I use in these videos.
The later videos after this one cover each part of the expansion chamber in more detail including the tuned length and outlet pipe and muffler etc.
As for bends on the header pipe, no this wont cause reflections back of the compression wave so long as the area of the pipe has no sudden changes which is why if you are making a header pipe bend using straight pipe you need to use mandrel bent pipe to ensure no kink on the pipe that will change the area of the pipe diameter..
Thank you now I kind of understand
Any questions feel free to ask.
I guess one of my questions would be about the effect nitro methane has on the pipe volume. I have been required to deop from 80% nitro to 10% per rules. What does that do to the volume and can it be offset with stinger size?
Nitro will effect the tuned length to some degree.
If you look at later video series on designing a chamber I go through the equations to calc tuned length.
2 values are effected by fuel which is "ratio of specific heats" and "individual gas constants" that are part of the equation.
in addition to average temperature of exhaust in the chamber.
As for chamber volume and stinger size, in Blairs equations those two factors are tied to BMEP of the engine in "Bar" pressure, they are not variable to fuel types or other factors.
If you know that KW of the engine you can calculate BMEP, the series I have here also gives the equations for that.
In short a higher BMEP requires a larger mid section in diameter to allows for higher pressure from the engine and a smaller outlet to offset that to stop ex port "spilling", this is also covered in the videos as to how and why that is.
I recently had a detonation issue with a KTM 300. Online, everyone who had an issue previously were told to lower compression or richen the jetting.
My problem was the pipe was a poor fit into the head. There was fuel/air escaping and there was evidence of that around the flange. But that shouldn’t affect jetting ( presumably) because both fuel and air were escaping, does that mean fresh air was coming back in where it was a poor seal. That seems unlikely to me, I would have thought the pressure inside the head would always be above the pressure outside.
Any thoughts?
If the wave can't move the air molecule then how do they push the air back in to the cylinder? thanks
The reason is the sonic wave is energy moving through the air no different than sound does and as it does it only disturbs the air molecules nearby.
As an example if a person shouts you can hear it some distance, yet the air molecules expelled from their mouth do not travel all that distance to your ear only the wave of energy does, and when it reaches your ear it disturbs the local air molecules in your ear.canal suffice to move your ear drum.
Likewise the energy wave moving through the pipe (from port to end of pipe and back) causes a local disturbance only to the exhaust gas molecules at the port at the moment it arrives back being the exhaust port just before it closes.
@@AuMechanic I see, thanks a lot :)
So... this is why a shorter exhaust gives better top end, and a longer one gives better bottom (about same volume)?
That is the effect of changing tuned length, but for a fixed pipe lengths the tuned length is also fixed and to get more top end or low end power other parts of the pipe are adjusted, the video series explains which part does what.
Great video! Quick question, how is the timing affected by mixture volume or is it purely RPM?
Tuned length is effected by temperature and mixtures.
Check out the more recent video ruclips.net/video/ppf5NQnIms4/видео.html
Covers calculating tuned length and how mixtures influence the sonic velocity.
So the expansion chamber only work efficiently at a one specific rpm numbers. Am I right?
Hi Azrul
No it operates over the effective "power band" of the engine that will also depend port port timing used, the design of the pipe will also determine how wide an RPM range it will be effective.
The video series covers the parts of the expansion chamber and which part effects below the power peak and up to the peak RPM and how those parts cause that effect.
This first video is just the basic outline of how they work to begin with.
AuMechanic I see. Thank you for your explanation. Looking forward to learn more. Cheers
If you have any questions watching the videos feel free to ask.
Happy to answer them.
Hello,
I am restoring 1987 Jawa 350, which is 2t motorcycle. Engine will be completly rebuilded, but I have a little bent exaust knees (its hard to get new ones for her). Some people say that it is not good for engine, but I have passed a lot of kilometers with those a little bent exaust with no problem. Can you help me and say what to do? Can I keep old pipes or I must spend a whole fortune to get new ones?
Best regrads from Montenegro.
One option for repairing pipes is to simply slice the pipe near the damaged sections and then use some sheet metal tools to beat out the dents and damage and then re-weld the sections back together with oxy acetylene.
There are also some videos on hydraulic repair of pipes using a pump but that is a bit expensive.
It all depends on the damage the pipes have, small dents in the belly section for example at not an issue for the pipes performance.
Damage the the header parts of the pipe nearer tot he engine can be an issue for performance.
@@AuMechanic I will try to cut the pipes near bent places and try to fix it, I have nothing to lose. Thank you for fast reply!
Hi... Would it be possible to put a silencer at the end of the outlet pipe? Would it affect the performance and how can I adjust output noise level and the size of a silencer? Thanks.
I am wandering how w difficult it would be to get this same scavenging effect and tuning length plus expansion chamber to apply to a 4 stroke engine with two opposing firing pistons ie making one pipe for 2 cylinders. To net the same timing.
Hi Mathieu, the one thing the expansion chambers relies on is a pressurised intake, without that the baffle taper at the end serves no purpose and you would simply use a megaphone in a single cylinder 4t.
On multiple cylinder engines a collector performs the function of increasing area at the end of the pipe, similarly to a megaphone in that it controls the area size increase at the end of the pipe to shape the expansion (suction) wave.
AuMechanic so can I read into your comment that potentially a supercharged 4 stroke engine might benefit from an expansion chamber. The other thing is a collector is often a large distance from the cylinder surely a matched primary length to the volume displacement of the exhaust stroke would be much shorter than most extractors generally are.
It has been tried according the Gordon Jennings but for some reason didn't last however its a given than without compressed intake the expansion chamber baffle cone on a 2t serves little purpose..
The difference being that a pressurised intake will cause intake spilling at the exhaust that the baffle cone reflection plugs.
Being the transfer and exhaust are both open for a good deal of time on the 2t charge spilling occurs.
It may be only where there is high amount of overlap on a 4t that plugging effect would come into play in a 4t with pressurised intake.
Re the collector, the length of the header is tuned for the suction wave to return at about TDC during intake and exhaust valve overlap from the ex opening time before BDC.
In the 2t the suction wave is timed from Ex open to just after BDC which is a lot shorter time in crank degree than the 4t and so you have a much longer tuned length in the 4t.
AuMechanic thanks. That Explains it all.
Is titanium the best for making a tuned pipe for heat consistency?
That would just be for weight reduction.
So how would a massive dent in the can affect the bike if at all ?
A big dent will effect pipe performance but it depends where it is.
Dents in the header section are bad where a dent in the middle section is not such a problem.
So this combustion chamber expansion doubles as the exhaust too? I've just started learning about engines.
No combustion occurs in the exhaust chamber.
The combustion chamber is the area above the piston inside the cylinder
@@AuMechanic So it's just an ovesizer exhaust pipe then.
Apart for the functions it does as described in the video, yes you could call it that
Buy the way.Are there any Vortex rings going on in a 2 stroke engine.The Pulse Jet makes them out the exhaust made in the cone after the combustion chamber.I could build devises to stop this but dont know if that will help thrust any.
You will get smoke rings out of any exhaust.
The operation of a pulse jet has a few similarities in so much as flow of compression waves however expansion chambers do not primarily operate on a resonance like the pulse jet does.
The source of the compression wave in the expansion chamber is from the pressure blow down leaving the exhaust port in a single pulse.
@@AuMechanic My 100mm D Z26 Italian Pulse jet pipe runs at 140 Hz a second or like 8400 rpm on a 2 stroke.I have a shorter Bailey Pulse jet running 240 per second.The longer the slower the pulse.I am shore its exactly the same principles.Speed of sound plus & minus the flow speed out the combustion chamber.Air is sucked back up the tail pipe as far as the combustion chamber in the return Vacuum wave.The vacuum wave is about - 6 psi.I had a 90mm PJ pipe split right at the end of the combustion chamber & this worked like a Venturi ,Arg Mentor or airplane wing sucking in air & making the Pipe run much hotter.I can inject extra fuel 3 in up the tail pipe to add 2 lbs thrust as this mixed with that air returning & is why the tail pipe always runs cold.I had a cone or flame holder in my German & Italian PJ pipes & after adding louvers to the cones Thrust increased.My idea was the shock waves could get through yet the incoming air & fuel would skip from louver to louver much like rain dropping over louvers on a house window.It worked very well.I will study your work & apply it to PJ theory.I think its a direct match.We don't have a reverse cone to add back pressure but the first diffuser cone works the same.The Pressure jet Engine used 3 tuned intakes to ram air into its combustion chamber.This power came from Nitrogen gas forcing LPG gas into its pipes at the speed of sound.I dont understand shis myself but it goes to show how much force tuned pipes can have.I have a Honda 350X ATC trike that makes a odd exhaust sound regardless what muffler I use.I think the different intake header pipes make this .If I CC each header pipe perhaps this sound will be much deeper like my single exhaust valve Yamaha YTM225.Do you think this could be possible.Its a single 350cc 4 valve head engine.
So what's the conclusion?? Is it good on a stock port of exhaust or it should be used only if we increase the ports sizes?? Plz say
Good question.
The percentage of performance improvement with an expansion chamber over a simple muffler will certainly be dictated by the engine performance to begin with..
An engine that has a low BMEP (covered later in the video series) is simply not able to generate a significant compression wave from which to get a reflected waves of any great amplitude.
And the engine will not likely spill excess mixtures at the exhaust at peak to have any great port plugging effect at the top of the power peak.
However, if you know the kW or HP for the given engine and swept volume you can calculate BMEP to give you some idea of how much gain you could expect.
Wow!! That was fast reply. Subbed u and thanks for the info. Love from india ✌🏼
Well, im into customisation have a look at my video if u have spare time :) thank u
The RXZ looks like it would get some benefits from an Expansion chamber.
I see the specs of 132 cc - 10.4 kW of power at 7,500 I calculate as about 6.3 Bar BMEP which is enough to get a chamber working reasonably well.
See latest video I show how to calculate BMEP.
Great video mate very helpful
Thanks for the comment
cool video. I was wondering how much power does the pipe really give you some say 55% some say 30% put i dont know who to belive :D . Also 2 stroke pistons are usually very round (at the top), put if you make it flat do you increase power?
Power will depend on the engine, an engine with low BMEP will not get as much from an expansion chamber is an engine with high BMEP, likewise and engine with a broad spread of power will have a low peak power.
It all depends on the use for the engine
So it there is no real average percentage of power improvements by adding an expansion chamber.
Hi,and thanks for the brilliant videos..could you tell me-does changing the length of the outlet pipe have much of an effect on performance?would it be OK to extend one outlet pipe on an rg250,and leave the other stock?cheers👍
No not at all
A much longer pipe will be slightly more restrictive than a short one but a small difference in pipe length wont make any difference.
The only thing the end pipe does is restrict the chamber outlet to determine pressure in the pipe, there is no wave action at all in the stinger pipe and has no effect on tuned length of the chamber..
@@AuMechanic thanks for the reply..much appreciated..cheers👌
Will having the wrong pipe on a two stroke make it run differently?
Yes it will, if you are going to fit a chamber to an engine it does not belong to at minimum ensure the tuned length of it is right for your engine otherwise the operating RPM range of the pipe you have could be way out of the ball park of the RPM range you engine produces power at, in which case the pipe will be less than useless and may even result in less power than a stock muffler.
See the video series I've done on How to Design an Expansion chamber, that gives you the sums you can do to calculate tuned length of your engines exhaust to match the pipe you are fitting to it with.
AuMechanic okay the reason I ask is I have a 2002 rm125 on a 90s frame that the right pipe won’t fit. It still runs mostly right just has the shortest power band ever compared to the other 125s I’ve owned was just looking for a solution
AuMechanic the pipe I have on it is from an older rm125
That short power band might be the pipe if it is not just a function of the engine itself..
If the pipe is too long or too short then exhaust wave pulses are out of sync with the power band of the engine and may cause the power loss at part of the normal power band ending up with a very short power band range.
If the tuned length is not right the baffle cone at the end for example might be sending a port plugging wave back before the engine has reached peak RPM causing a loss of power that may feel like the power band has stopped early and not revving out at full power.
Thanks for this video. I have a question: What's the result if you shorten the header section of an original pipe to make it fit another type of moped? It's shortened by 8cm approximately. Thnx!
Making the pipe shorter will raise the effective RPM range the pipe is tuned for.
Check the engine it came off and establish the peak RPM on it, if the peak RPM of the one you are fitting is too is higher then you may get away with it.
You can use the freeware pipe calc to input the engine specs of each engine to see what the tuned length of the pipe is on the bike you got the pipe form and should be on the engine you are fitting it to. Then you can basically raise the RPM value in the calculations for the new engine until the tuned length equals the tuned length for the old engine the piep came from to see how far out it will be with that much removed.
So does your pipe need to be completely suspended or can it rest on rubber, and would a cracked pipe cause premature det?
I prefer to use spring hook mounts myself to allow for some thermal expansion as well as vibration isolation which you want to reduce as much as possible being reflected back to the engine as vibration at the combustion chamber is bad for power.
As for the spigot mount for pipe to head, TZ engines for example used O rings to seal but you can use silicone on a slip on spigot at the header.
@@AuMechanic Ok, Thanks for this info.
Why does sonic wave ignores the exhaust but pushes back the air with fuel?
The gas is a mass or air molecules, the wave is energy moving through the air mass.
The wave raises or lowers the pressure of the gas only at the location of the wave.
The same as a wave in the ocean causes a rise pr trough in the water level where the wave is.
So the sonic wave doesn't push the gas anywhere, if the face of the wave arrives at the port just before it closes, which it does if timed right by the tuned length of the pipe. Then the leading edge of the wave peak will block fresh fuel and air gas mixture from spilling out of the cylinder into the port as the port closes thus trapping more of it in the cylinder resulting in more power.
Another example
Image a gate at the edge of a harbor that allows or stops water from moving out into a channel of water and there is a boat drifting with the current that is about to drift through the gate into the channel and a wave comes back up the channel against the current. The wave arrives at the gate just as the boat is about to go through it, at that moment the front of the wave cause the forward speed of the boat to slow or stall until the peak of the wave has passed it but before the wave has passed by the boat the gate suddenly closes trapping the boat in the harbor which, if the wave had not arrived and slowed the boat momentarily, the boat would have passed through the gate just before it shut into the channel.
The harbor is the cylinder and the boat is the fresh intake charge that is about the spill out into the channel which is the exhaust.
That is an excellent answer. Thank you@
Which chamber is best for Suzuki max 100 bike?????
Interesting ...Is there a way to increase the HP by moding the muffler pipe? Or header pipe ?
That really depends on the pipe it has and if the engine has any mods to it like higher port timing.
If the pipe is dead stock road pipe for example you may make some gains by putting a muffler on the end that breaths a bit easier (chainsaw would be one example) but if it has an expansion chamber already then it is likely designed for that engine port timing and exhaust port size.
What diameter the outlet pipe should be compared to the header pipe ?
Outlet pipe ratio is to the port area not the header, the outlet pipe area (convert that to diameter) is 0.6 to 0.7 x the area of the exhaust port window area, see later videos on how to measure the port window area as well as the video specifically on outlet pipes. Or use the pipe calc software linked in the description section under the video.
How can you make a 70cc quieter
Will adding more stuffing reduce the power by a huge %
If it is a straight through muffler and you are not changing the diameter of it then repacking the absorption maternal should not make any difference.
If it is already full of material then repacking it may not do anything or sound reduction in which case you need to look at a larger muffler.
Amazing what you can do with MS paint
Its pretty handy, I'm just trying to figure out how to do animations.
do shorten header pipe increase high rpm power, and raise rpm?
Shorter total pipe length (tuned length) will raise the effective RPM range the pipe works at.
In spring Karting a flexible header section is used and they are changed to raise and lower the RPM the pipe works at.
Awesome video!!!!
Thankyou so much
Thanks for the comment
does the length of the header pipe have an effect on the performance?
Any change in the header length would position the diffuser closer or farther away from the port and would effect the timing of the first expansion wave returning so the yes it would.
@@AuMechanic so if there was no header, the expansion chamber would work as well and it would be just a matter of timing? In other words, is the header essential for the exhaust to work properly?
@@Shulkyl Not really possible as the port length is in effect part of the header length in so much as it also provides some distance between the start of the diffuser and the port window at the cylinder.
And for example if the engine RPM was very high and EGT high and the port fairly long then the pipe itself would have a very short header if at all.
@@AuMechanicok. There are these exhausts on ebay for motorized bikes called "banana exhaust". They kind of have an expansion chamber but little to no header at all
@@Shulkyl Yes I know the pipe you refer to and the first time I saw them I concluded they were more "show" than "go".
Those motorised bike engines have a fairly low peak RPM which would dictate a fairly long tuned length and this longer pipe then higher revving engines.
You could download the free pipe software I wrote (see link below videos) and make some calculations based on your engine that would allow you to figure out at least how long you would expect the header to be on a properly tuned chamber as well as the total length.
Can I use an exhaust system from a 125 2 stroke for a 185 or should I use one from a 400cc
Not if you want it to work as an expansion chamber.
You might chance the tuned lengths being the same but the diameters of the pipe section will not be even close to yours.
See the other videos I have that cover those topics and you could even try the free software to pipe dimension you would need for your engine that might help you find another pipe that is a suitable match.
thanks just started my mid-life change or life and 2- and my lathe r my chouses
Wen come out of head init the exhaust does it need back compression going back in two the head
Yes for expansion chamber exhaust like this.
If you watch later videos Ive done particularly the one on outlet pipes the function of back pressure is covered.
In Dutch een tweetact heeft tegendruk nodig..daarom die expansie uitlaat jes ???? Ik moet ze niet !!!
Thought this was mentioned to simplify expansion chambers ...now I'm working about tuned length pipes ect lol
It's a trap ;-)
AuMechanic I still love it bruv ...it's not really a bad thing as I was thinking about tuned length pipe for my moterised bike ...I'm designing a chamber as I'm sure U no they come with a Verry shity exhaust set up
Yeah the stock exhausts are not much chop
I have a freeware pipe calculator program that incorporates all the equations used in the later videos too, there is a link in the description section.
AuMechanic thanx man I'll give the software a go on my next pipe for my ts185
Not depression, rarification or adiabatic depressurization. Depressions occur in open atmospheres, not walled chambers.
A depression can be be created by pushing a finger into sand to cause a depression so the terms depression itself has various contexts.A "depression" in this use is created in the pressure transducer time scale as read by an oscilloscope.
A good pipe will give 1 to 2 hp a good port jop will give 5 to 10hp on a mx bike.dont forget your port timing.
Whatever pipe you have it has to be designed based on the port area and timing or it wont be a "good" pipe.
Thanks Good Work!
So I just purchased my first pipe for me 66cc motor. It’s an mz65 and I’m having issues with it hitting the head. From what I’m understanding if I shorten the header a little bit it will favor higher rpms? Can I shorten the header safely? And if not, or period, could I bend the header? Thank you
Bending the header would be preferable but only if you can ensure that will not kink the header pipe at all, it is important to retain the cross sectional area of the pipe (its internal diameter) through its length specially the header.
Usually using a mandrel inside the pipe to bend it, if it is only a small bend and no risk of kinking the pipe at all or deforming it then you might be ok with just a bit of heat.
Shortening it however will change the tuned lengths and short will favor higher RPM.
You can use the calculator software to get a rough idea of how much the RPM peak will be changed by a length change to see how much you can remove safely without effecting RPM range too much.
AuMechanic thanks ou very much!