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During the ’73-'76 years I raced motor-cross with Honda's CR Elsinore in both 125cc -250cc class events, they were beautifully constructed bikes that were the closest thing to factory works bikes money could buy straight off the show room floor. It had one major flaw in the design of the expansion chamber exhaust pipe, Honda engineers designed the pipe to run under the engine cradle, so each race event that had lots of jumps I'd crush the expansion chamber as well as my nads 😢 So once race day was over and was able to walk upright and speak without a high pitch, the cleaning began hosing the mud off the bike then the damage assessment began, I became proficient cutting out the flattened damaged portions and wire welding mild steel patches that matched the contours of the original pipe, after that sprayed it with heat resistant flat black paint. By the next race day the bikes were looking brand new. There was no internet back in the day, information relied on the phone or letter writing and what one could get through magazines, fortunately and with a bit of luck I was able to get a peak and dimensions of Honda's factory works engine head and barrel, though being dissimilar in port design and shape I was able to cc volume match it, few porting stones I was able to increase the abrupt and narrow power band with a torquier and wider power band that kept me competitive during the winter of '75 when Yamaha released with their new white tanked mono-shocked YZ series Motorcross bikes which was a game changer over the rough stuff, no longer was engine brute power the sole reason for winning, it was combination of frame, long travel front forks and rear mono shocked cantilever suspension. The good old days they were.
Perhaps needs a more accurate title than just "two stroke" - obviously this is a crankcase intake/transfer 2-stroke, but there are diesel 2-strokes, and mazda even has a working poppet-valve petrol 2-stroke.
I am an 82 years old American who rode 2 stroke trail bikes in the Rocky Mountains of Montana and Wyoming. I never really understood how the shape of the exaust pipe worked. It has been many years since I stopped riding bikes. Today's video, as all of your videos, was very informative and entertaining. Thank you.
I'm 62 & still have my '84 XR250R 4- stroke. *_The REASON I haven't ridden it the past 7 years_* is because at age 55, I realized... if I get even the slightest injury, I will not be able to work 100% at my very physically, demanding/gruelling job & NOT GET A paycheck. No work=NO PAY. Since I'm at an age where: 1) I have a finite number of years working at the highest physical level possible & 2) I am not satisfied with my retirement savings AMOUNT... I do not want to injure myself, be unable to work & be unable to acquire the most retirement savings possible in a shortening time frame. I do start the bike annually & ride it in a circle for 5-10 minutes to keep it "alive". 30 years ago i broke my collar bone by merely falling over to the side at 2 mph on this bike. The recovery was very, very long due to no surgery.
@@jeffrandolf5673 Man you only live once. The average person has an injury producing accident every 70 years of street riding. Approaching life from the viewpoint of micro economics is very limiting and soul crushing.. Get some good gear and go make the most of your short time on this earth. My 2 cents.
@@chrispy1965 Some teachers are in a job, other teachers are educators. This guy is an educator, which can't be taught to be fair. I had at least one perfect example of someone who taught and had no business doing so growing up back in high school, she had a job and she didn't care about it. Another teacher was also doing a job but they spent time trying to do it right, they cared even if it wasn't a natural thing to them. And I also had several amazing teachers who truly were educators.
I remember there was one point a long time ago where he said he felt his accent got in the way of his ability to communicate effectively sometimes. Back then and still now though, he is articulating complex concepts that I as someone who is reasonably intelligent, but ain't smart, am able to learn something every time I tune in.
@@chrispy1965I've spent most of my 28 years of existence as a student. The majority of teachers I've had, both in public schools and universities, clearly did not care about the material they were trying to teach, nor did they care whether it made sense or was interesting to their students. They were just going through the motions enough to meet the bare requirements of their curriculum in order to get a paycheck. Teachers like that really make you appreciate when you get a fantastic teacher who loves their job and is damn good at it.
Excellent description. I have a university degree in Physics and my senior thesis was titled, "Tuned Exhaust in Loop Scavenged Two-Stroke Engines". I got the best grade in my class because I did the theoretical work AND the practical application work (by cutting, rolling and welding exhausts of various shapes for a 2-stroke model aircraft engine). I even built a small dynamometer (using a small disc brake and a fishing spring scale) to measure the power from various shape pipes. The only thing I would add is that the varying speed of sound (depending on ambient pressure and temperature) does have an effect on the optimal shape of the pipe (when measuring peak power). I went to university in the northeastern part of the United States and did my senior thesis in the fall semester when the temperature in the early morning was around 0 C, and afternoon temperatures were over 20 C. For peak power, I built a "morning pipe" and an "afternoon pipe" 🤣
@@THESLlCK AAXA101 is correct it is mixed and wrong. The visual example is not correct. The sound of the engine has NOTHING to do with he pipe design. His engine stuttering will happen on ANY 2 stroke at any RPM and is more about the throttle position and a simple fact of the port timing and the engine not being able to pull a full charge into the cylinder. The closed throttle chokes the engine down so the exhaust cannot do what it is designed to do At partial throttle the cylinder is getting fuel but the port timing is not going to allow the exhaust work fully and the exhaust design only works fully at wide open throttle as the specific RPM range it has been designed for. If the exhaust has been designed to work at 8000rpm or 12,000 rpm then it will not simple increase torque or power at lower RPM by opening the throttle. Yes power valves do help but this is port timing and NOT due to exhaust design.
I have understood expansion chamber exhaust pipes since learning about them by reading all the motorcycle magazines in the early 1970's. I have always thought of them as a "Tuned device", like a musical instrument. Never have I been able to explain it as well as you have. Foot note: there was a private racing team in the seventies running a Bridgestone 350cc twin two stroke with the cylinders turned around backwards, making the exhaust ports face towards the rear of the motorcycle. This caused their exhaust pipes to be too long and it wouldn't pass tech inspection. They cut off the stingers (the small pipe at the end of the exhaust), shoved them inside the expansion chambers and welded them in place. The result was no discernable loss of power but a greatly reduced noise output. As one of their competitors stated, "That thing doesn't make much noise but its fast as hell!" An entertaining anecdote from the 1970's for you.
I did this exact same thing (i.e. cutting off the "stinger pipe" and re-welding it inside the convergent cone) to my TZ250 Yamaha... now that I'm an old man, my hearing thanks me for this insight I had as a young man!
I’ve been with you since the beginning of this channel and it is my opinion that this was your most effective video of the series. I’m not into motorcycles, or two strokes in particular, but I now feel qualified to pass this information on to some of my younger friends who are. Thank you for this.
He is excellent. There is another guy who does fantastic engine videos. He's American. Not so busy at it recently I think. I will get his name later- can't remember it.
20:24 bro really said "tried" as if he didn't just explain it in a way that made it seem like an incredibly simple concept. Every time I watch one of his videos I am amazed at how well he explains things and how he makes them all feel simple, he is truly a genius.
What a brilliant explanation of how a 2 stroke works, I started my mechanics on them then 4 stroke bike and also car / truck engines and this has to be one of the best and easiest to follow tutorials on the subject I have seen.
I have never heard someone explain these expansion pipes so succinctly and clearly. Thank you for making this video. I haven’t ridden a 2 stroke in a while, but maybe I need to get back on one.
@@d4a Direct fuel injection like the Rotax ETEC 2-stroke engine that Skidoo has been using in their snowmobiles for quite some time now has solved the problem of the air-fuel mixture escaping from the open exhaust port.
Since riding dirt bikes in the early 90s... I always wondered what the pipe shapes were for. Unfortunately the internet didn't really exist back then. 12yr old me thanks you for the info!
The explanation is in the name itself they are called resonator pipes orr resonator exhaust. It took me 5 minutes of thinking to figure it out how it works 40 years ago when I was a teenager. And I understood the same thing as in this video. I have had a 50cc bike with a resonator, that had about 11 horsepower at 13,500 RPM. Top speed 120 Km/h I love that bike.
Back then we had things called book stores and libraries. Amazing what you could find buried in the back of an old book store. Even my high school library had a book on 2 stroke engines.
Jesus why is everyone giving this guy shit? When you're 12 years-old would you rather be riding or going to the library to look up every small curiosity you have? The internet makes answering questions like this a lot more convenient. Don't be a hater.
Extremely well explained. And to be fair, i never considered the expansion of the wave to create negative pressure wave but it makes perfect sense, there is a "void" that is left behind as the positive wave expands. They do use acoustic resonance with 4 stroke too, there the positive pressure wave is reflected back so that it hits the closed exhaust valve just before it opens, and is reflected back, and this creates a low pressure zone behind it that helps to suck exhaust gases out.
This is why you'll get specific "dead" chambers on either end of the engine nowadays; usually one or two plastic chambers on the intake side and one section of tube tee'd and capped on the exhaust. They often aren't for performance specifically, instead meant to reduce overall sound signature, but incedentally also increase efficiency because they disrupt aberrant reflected waves.
Yeah, same on intake. That's why those throttle trumpets require tuning. Plus on F1 cars and motorcycles you have a tiny hole to suck in air that expands later in the air box because slow air has more pressure.
@@Mis73rRand0m That is fascinating. I'm sound engineer myself but also have worked in wind instrument repair shop.. There are so many things that overlap between sound and vehicles. Like, the equations that work to describe what suspension is doing has a ton of similarities with equations that are used to for ex to design speakers, and filters. Resonances, critical damping, hysteresis, saturation...
I am in my last 4 months of a 3½ year apprenticeship as a car mechanic. During this time, the videos from this series have been the best explanation for engine principles. Fast superior to school classes. Thank you very much for this series! Keep on!
Absolutely incredible video, I rode 2 stroke for many years back in the 90's and 2000's and always understood that the pipe and shape of it helped with power, but never understood why. This video explained it all so well, and not only that, the whole lesson on sound waves was incredibly fascinating too. I'll be watching a lot more of your videos going forward. Thank you!
Great explanation, I built expansion chambers in the 70's for two strokes when they were unavailable for most bikes. The calculations were widely available at the time but fairly complex. The first chamber I made was for a mid 70's Suzuki TS185 formed from car panels by hand and oxy welded. It went like a rocket.
Any idea why the Exhaust on a Trabant only expands at the beginning but doesnt compress at the end? its a weird shape to explain, sorry. ill try to crudely draw it, hope it works on mobile too (here are the two cylinders) I I I I__________________________________________ I I __________________________ I I I________/ I I____________ I I \__________________________ I I__________________________ ______________I I I (to the mufflers)
Wow that's cool!. That was my first bike a 1974 TS185 I saw it in my neighbor's garage when I was mowing his lawn it needed a lot of help I totally rebuilt the whole bike in 1996. I always thought it needed a custom exhaust
@@Handyman1199 My guess is the muffler portion at the end is acting like the tapering end at the rear (without seeing it). It would be more efficient to have the classical shape with a silencer on the end, but I think you could get a weight reduction and overall shorter length with a design that uses the muffler/silencer to help reflect sound waves back (and still get a large portion of the efficiency gains required.) My two cents.
@@BarryJTaylor Thats what they do on Trabants when pushing the 600cc to 70ish HP, use two giant individual resonance chambers instead of the one inside the "pre-muffler". The original one is apperantly designed to increase low end toque, whilst also supplying heat to the cabin heater via a second shell (both the header and the pre-muffler/resonance chamber have a second shell, the engine fan blows air into them. the parts heat the air before pushing it into a big silencer, from where it enters the cabin)
Just finished the whole video. The examples you use are phenomenal. You’re truly a wonderful teacher and one of my favorite creators on this platform! Always a good day when D4A uploads!!
I used to desert race two strokes almost 50 years ago. I sort of understood how they worked and knew and experienced "riding on the pipe", but I didn't really understand it until this video! Absolutely the clearest explanation of how two strokes work and especially how expansion chambers actually work.
Cheers from Brazil! I'm 31 years old and always loved motorcycles. I've always been curious about 2 stroke engines (since I have several bikes, including a 1989 Yamaha DT180Z which I restored) and in my early days of internet those exhaust shapes was one of my first thins that I searched about on wikipedia, I remember using a printed English to Portuguese dictionary to translate the words... Now there's so much good content around, and you're part of that! As a mechanic engineer I think how much more information teenagers from this era can use to understand the world and machine around. You guys are really heros, keep it up with the good content!
I'm glad you literally spelled out "impedance" all over the place, because I swear what you were telling me verbally is that my exhaust couldn't get it up! Regardless, this is one of the best explanations I have ever seen or heard. Much respect! Cheers 🍻
Traditionally in English first "e" is long, but I ain't gonna give the guy any crap for pronunciation since it's pretty clear that English ain't his mother tongue.
This is so crazy! I randomly thought of 2 stroke bikes and have been watching a few videos, and then I log into my account to see this uploaded 13 min ago! The timing couldnt be anymore perfect friend. And yes, I was thinking why their pipes were that way
I finally got it after the second watch. Ive always wondered what the point was of its shape, yet have never looked for an explination. Im glad it was you that taught me the reasoning behind this clever piece of engineering🙏
Fantastic video, and also the first genuinely well made explanation of two stroke exhausts I've yet seen on RU-vid. I have been trying to learn more about the mechanics of two stroke engines for the better part of a year, and while there are many detailed videos most of them are borderline unwatchable due to scripting and production. I would love to see more content covering other two stroke details, especially stuff like porting, ignition mapping, and power valves. While the information on performance two stroke engines does exist online, it's not very accessible and I want to see someone change that.
Riding 4 Answers once again knocks it out of the park. All that remains is to get you riding a desmo and the world will be perfect.))) R4A has always been one of my favorite channels... Even when it was D4A.)))
I’m a retired(72 years old)meat cutter working in a motorcycle shop as an assembler. I had asked my coworkers about the two stroke exhaust pipe. The answer they gave wasn’t as clear or concise enough for me to understand the benefits of the expansion chamber. Thanks for your wonderful video.
Being into snowmobiling in my youth I always knew that the exhaust pipes affected the power band but I didn't really understand the exact science behind it. This video is an absolutely perfect explanation of the entire process. You've got my subscription!
I have two two strokes (RD350LC and RD400). I spent quite a lot of time building chambers for the RD400 and trying to understand what was going on. I had the basics but you have brought it to a new level. Thank you.
I knew that 2-stroke engines used sound waves to keep more mixture inside the cylinder, but your explanation made it crystal clear how it happens! Now, let's make a video about YPVS???
I am so happy to see this channel thriving, mostly because its great information presented extremely well and it helps fund a sweet MR2 project. But I also get to say "I was here when he only had a few hundred subscribers!" and everyone enjoys the smug satisfaction of knowing about something great before everyone else.
It's a shame tat only only 1 thumps up can be given This was spot on and my thump up is worth a thousands Keep up the output I wish I had you as a teacher. To late I am catching up
When I was a kid, my friends and I who had dirt bikes always thought the two-stroke "powerband" was a physical component located somewhere in the engine that would kick in when you increased the throttle lol. Later learned it was wrong, but never truly understood it until seeing this video. Great explanation!
I have searched for an informed, properly explained answer, supported by factual information, for over 3 decades! Finally!! Finally at 44 years young I get that answer. I love your channel my friend. Educated, accurate, humble, clear and calmly explained with great illustrations. You provide an invaluable resource, my friend. Know that you are appreciated. Know this work is important and impactful. Thank you.
The easiest way to think of a 2 stroke expansion chamber is that it's a non mechanical turbo, you can literally double your horse power when you add one of these exhausts.
I think of it as a self-scavanged exhaust; instead of using other cylinders' gasses to create a pressure differential across the exhaust port, it uses clever resonance to help itself out.
@@Mis73rRand0m Yup it very much is a scavenger system, and there is a very cool story behind it that sounds like a Hollywood movie. The inventor was a russian rocket scientist who defected during a grand Prix race.
@@bazzingabomb Actually the man was East German, Walter Kaaden - an engineer working for MZ motorcycle company. And Walter didn't defect, his rider (Ernst Degner) defected and brought the technology to Suzuki.
@@danielklopp7007 you are right, I said russian but meant soviet as east Germany was part of the iron curtain back then. I also new about mz and and the suzuki connection but not many people outside of Europe know about mz. But thanks for clearing up my mistake.
I’ve learned more about two stroke engine function and how they do not waste as much fuel as one would expect, and why the funny shaped shaped exhaust is intentional, in this one video compared to all the others I’ve seen. Well spent 21+ minutes! Your videos are very informative and educational- keep up the excellent work!!
I'm not an automotive mechanic but I believe I am somewhat knowledgeable, just the same, ... a back yard mechanic if you will but with your methods of explanation I go to sleep at night with a heck of lot more understanding of 'mechanics' ! Great video, as always. ... again, thanks.
What incredible timing for you to release this video. I just recently went down the rabbit hole of learning about exhaust scavenging and back pressure and why long tube headers add so much power on v8 engines. Its crazy to think that something so detrimental to making power on a 4 stroke engine can essentially hsve the opposite effect on a 2 stroke motor. Great video and great explanation! You honestly made the principles of scavenging make way more sence to me as well!
Way back in 1976, I, as a college-bound high school student, bought a book on 2-stroke exhaust design. That inspired me to pursue mechanical engineering because I wanted to design "go fast"" parts for dirt bikes. I ended up having a career as a software engineer for engineering companies, but that bit of motorhead engineer is still there (why I watch this channel)...
I teach some foundations of musical acoustics at the university level and I really appreciate this video. By far it is one of the best from your channel and I will suggest it to students who have an interest in engines!
What an amazing description! I work with radio frequency electronics and the concept of “acoustic impedance” is one I’ve never heard before. It really lets you look at the entire exhaust as a transmission line.
Thought I knew how 2T worked. Nope..... Thanks man. You took a very complicated subject and made it digestible to the average person. 10.5/10 Edit: Oh and 4T rules lol !!
One of the best videos I’ve watched in recent memory. Taught me something I’ve always wondered about, gave me terminology and vocabulary I never had, then made me laugh with the goggles falling through the helmet like I’ve done a thousand times. All with top notch visualizations to help it all be much more consumable. Thank you again for making this content and being bold enough to share it with the world.
This has to be one of your slickest vieos yet, and as ever, extremely informative. Congratulations for that. Not being particularly interested in bikes I didn't think I'd be so interested, but it answers one of those questions what one never gets around to researching. Why do 2 strokes cough and splutter. Actually the trials do look fun. Great work!
I did already know how two-stroke exhaust systems worked but I have never seen such a clear explanation before. I will be encouraging my students to watch your video and can then, hopefully, answer any questions they ask afterwards. Thanks for such a well made and presented video.
Awesome explanation, your skill as an online teacher is improving greatly. Best explanation I have heard yet, I remember back when FMF started making the 'fatty' pipes that looked like someone beat the crap out of them from the inside, all kinds of bulges and odd bends. The FMF reps had a hard time explaining why it was more than just a weird look.
I knew the expansion chamber played a part to some extent, but the explanation and visuals really solidified my assumptions and primitive understanding of how the pipe really works. This is the video i didnt know i needed on a random October Sunday morning. Thanks!
This is easiest example to why your one of my top youtubers for a number of years, clear and informative examples to show how engineering works, keep up the great work matey 🇦🇺
Hey there, you have a remarkable talent for taking complex mechanical topics and breaking them down in a simple, easy-to-understand way. As a high school Electronics teacher, I've always prided myself on delivering clear lessons, but I have to admit, you've surpassed my skills when it comes to making challenging concepts accessible. Kudos to you! Over the years, I've attracted many high-achieving students, and I remember quite a few coming to me for help with Grade 12 Physics, particularly on how to simplify a complex resistor circuit into a single equivalent resistor. I would demonstrate this using diagrams, gradually replacing parallel and series resistors with their equivalent until the entire circuit was reduced to one representative resistor. I’m sure you’re familiar with this process, but I’m explaining it for any readers who might not be. I noticed that the Physics teacher from Lebanon would also used this approach, but his students struggled to grasp the concept. What was different? The key difference was in pronunciation. The teacher pronounced equivalent "e-qui-vah-lent" as "e qui-vay-lent," similar to how "valent" is pronounced in "valence electron." English, as we know, can be a confusing language for non-native speakers. Although English isn't my first language either, I attended a school where all the professors were native North American English speakers, so I learned to mimic the North American pronunciation. Why does this matter? Like that Physics teacher, you and I are non-native English speakers and can sometimes mispronounce words if we haven’t heard the correct pronunciation. This can make it difficult for listeners to fully understand what’s being taught. For instance, the word "impedance," which means to impede or restrict, is pronounced "im-pee-dence," not "im-pah-dance." Mispronunciations can unintentionally confuse students. That said, it's worth noting that pronunciations can vary across English-speaking countries. For example, "aluminum" is pronounced differently in the UK. So, this may not always apply universally. I want to emphasize that I have immense respect for your skills in sharing knowledge, and I mean no disrespect at all. It's often the small details that separate a superstar from a good professional-those little things can make all the difference. Peace bro
I ride a road legal 1998 Yamaha DT230 and love two strokes! I had no idea that the power band was actually just the timing of pressure waves and RPM aligning. So in theory you can adjust where the power band is by adjusting the position and size of the expansion chamber. Fascinating! Thanks for the video.
During WW2 they directed the exhaust backwards on the spitfires, mustangs and corsairs. The engines exhaust was so powerful it actually added thrust to the aircraft. You just needed to lower the pressure close to atmospheric as possible to avoid jet wash thrust losses.
I'm doing my apprenticeship as a mechanic at Mercedes in germany right now and it's always so funny when I'm in school and know about what feels like 90% of the stuff already because I watch every video of you and do so much work on my cars ^^ (I bought a aw11 with a friend wich we are fixing up a few years back now because we saw your ITB video and that started it all ^^)
Yamaha IT465 I had never really had a power band It was power from just open throttle to to max RPM where the power delivery did fall off rapidly gone out of resonance Altering the exhaust chamber makes a huge difference to performance. Excellent video of explanation.
My real world experience with this was on my 2 stroke RC car. Stock 23cc engine, normal muffler (just a box) and it was pretty weak. I did end up putting a larger bore "head" and piston on it, but for a short time I also put a tuned pipe on that 23cc setup and the difference in power was insane, all from 2ft of pipe.
this is precisely why different exhaust pipes can make a huge difference in the behavior of a 2 stroke engine. For example, both my wife and I ride Banshees ( twin cylinder 2 stroke quads). I run a more drag style pipe and my wife has a mid range pipe. My Banshee revs about 1500-2000 rpms higher than hers and has much more top end power while hers has less top end, the power band comes in sooner and has way more low end torque than mine. My power band is like a light switch. All of these differences despite having almost identical engine builds. 2 strokes are truly amazing pieces of engineering.
the exhaust is possibly the primary reason i love 2 strokes so much. it is complicated to get right, but when it works it transforms the engine into what could be described as the most visceral power plant, both power output, power delivery and sound.
I've always known it was the back pressure in the pipe that what was needed for two stokes to work, but i didn't realize it was actually a sound wave doing that. Makes so much sense now that i think about it. Great explanation!
This explanation is excellent, now I understand why not just the shape and size of the expansion chamber influences the powerband, but also why the length of the parallel part into the chamber and the stinger is so important.
I was always fascinated in two strokes since my Simson s51 Haha love them small stinkers 😄 They got a powerband like they have a turbo And they are so simple to repair and sound nice with a small engine
Great description. I was surprised to hear the discussion extended to "impedences." That was really great an is essential to understand what's going on. Notice how trumpets, trombones, etc, have a flared opening to the air....it's for impedance matching to avoid a reflection back into the instrument. BTW. In American English, it's pronounced "impee..dance."
This video just appeared on my list of recommended videos and I subscribed to your channel instantly. I'm not a mechanic, but this video was very captivating, now I have to watch all of your videos. 👍👍👍👍👍👍
Love your videos at always. Yes... that exhaust shape is probably the second most influential aspects of the 2 stroke engine's powerband after the bore & stroke. Different shapes of exhaust will change the power band. People get different exhausts to get different effects on the power band... whether they want to improve low, mid, or high rev range. Changing an exhaust is one of the most common tuning upgrades done to 2 stroke dirtbikes.
In the mid to late 70's I raced enduro go karts and one of the most effective ways to make those old McCullough chain saw motors delver outsized power was and adjustable expansion chamber. A lever mounted on the steering wheel allowed you to shorten the 'pipe' as engine speed increased adding significant power throughout the powerband. Never totally understood that it was sound that was being utilized before. For motorcycle riders and fans of Cycle magazine, I'm sure Kevin Cameron would approve of this video.
That was a pretty good job explaining the expansion chamber. It would have been nice to hear the bike @ 9,000 + - rpm full throttle. I am old, and I was lucky enough to have been around in the original two stroke street bike days. I owned a Kawasaki S-2 350 cc triple, and a H-2 750 triple. of course those bikes didn't have power valves. So their "supersonic" power increase happened only because of the expansion chambers (and porting). The stock mufflers were horribly inefficient (and heavy). My 350 doubled its power output, AND fuel mileage after being ported, bigger carbs, and exchanging the mufflers for expansion chambers. I couldn't tell you if fuel mileage increased on the 750, because I installed the expansion chambers right after buying it. I LOVE 2 stokes! It has always been my dream to build a flat 8 cylinder liquid cooled two stroke 4.0 liter engine with power valves to install into a mid engine tube chassis car. But I never had enough money for that kind of a project. The flat 8 engine is the best case I could come up with so there would be room for 8 expansion chambers. I believe that 750 hp would not be an unreasonable output from such an engine. Maybe even 1000 hp.
