How the TWO-STROKE EXPANSION CHAMBER WORKS and Where It Came From (call it Acoustic Supercharging)

[@drgallup]

I got my copy of Gordon Jennings Two Stroke Tuners Handbook in '73 while in high school. I got a greens mower 2 stroke engine from the golf course across the street and convinced my physics teacher to buy a small dyno from Fisher Scientific. Jennings book had equations for sizing ports for the RPM you wanted to make peak torque. I measured the engine I had and back solved the equations to predict the peak torque RPM and others to predict how much torque it would make. Then we ran the engine on the dyno and compared the results with the predictions. The correlation was pretty good. Later in college my room mate and I used the book to to port our dirt bikes. I even made my own expansion chamber. There was a mail order company that would roll cones to your specifications. I managed to raise the peak power rpm and narrow the power band to the point that it couldn't pull the 1-2 shift while hill climbing with the wide ratio gear box. All a learning experience. Later when I had a '88 CR500R it had such a wide power band but narrow ratio gear box I put in a wide ratio box to get a better 1st gear for woods riding. That bike was the biggest thrill ever, even better than my '81 RD350L/C. Wish I still had my copy of Two Stroke Tuners Handbook, it's long out of print and worth a small fortune. But I do have a PDF of it.

[@MikeBaca-rs8ij]

Is this the reason that Suzuki utilized a form of gas porting at the top ring of the piston to force the top compression ring to seal against the cylinder wall

[@christophercurry7410]

My dad and I built great running dirt bikes and snowmobiles based on Gordon’s book and sound advice from Kevin. With a few tricks of our own to get them through stock class tech inspection.

[@christophercurry7410]

Thanks Mark and Kevin. I’m hoping 2-stroke technology regains the popularity it once enjoyed in motorcycling. Snowmobilers still embrace the lightweight and high power output of modern 2-stroke tech.

[@blantant]

Would be amazing if they could make a breakthrough to make it "clean" , yet still cheap to manufacture and simplistic

[@matthewfredrickmfkrz1934]

Hp tuners is being lame about 2 stroke support found on the forum somebody to bug but they keep saying wait for updates I got the link

[@tonn333]

​@@matthewfredrickmfkrz1934what a horrendous sentence, if it can be called that.

[@matthewfredrickmfkrz1934]

@tonn333 sorry Mr punctuation but gatekeepers are gatekeeping 2 strokes from being fully tunable electronically I don't have time for grammar

[@tonn333]

@@matthewfredrickmfkrz1934 if you don't have time to bother about your message being understandable, then why bother at all I wonder.

[@wapartist]

I could listen to this man explain anything for days. Even a refrigerator manual or something it would become super interesting!

[@ocavant]

I learn more from this bike channel then any other automotive/motorcycle channel I watch. Thank you!

[@micyclesport]

Mark really an excellent job of pausing to explain Mr. Cameron's visual aids and add background info!!!! The CW podcast has been a huge win in the signal to noise ratio. I'm taking moustache classes.

[@christophercurry7410]

Great content! High performance two-strokes will always be close to my heart.

[@alexdesamsonow822]

Awesome podcast as always! Thanks Mark and Kevin! I always wanted to listen to Kevin and see him in person since I was a kid! This is pretty damn close!!! Love this podcast series don’t stop please!

[@nealdaleyjr7625]

The more of these episodes I watch the smarter I get. By the time I'm 75 years old I will be brilliant! Thanks...

[@matthewtaylor4956]

absolutely fantastic. Kevin is a literal encyclopedia of motorcycle information. Love this channel.

[@ooyginyardel4835]

He has an amazing knowledge of radial aircraft engines also!

[@engranger]

You get a ++ every time I hear Gordon Jennings name. I still have my copy of the 2 stroke tuners handbook (that I paid $5 for, from an ad in the back Cycle magazine). In it on the blank pages in the back are my calculations to derive some of the equations in the book. I was an engineering student at the time and this stuff was a lot less boring than the textbook examples. Absolutely loved it. I have to say I was partial to Cycle magazine at the time. I thought the technical material was the best and I couldn't wait to see what label they would put on Jennings in the next edition. Keep up the good work, brings back so many fond memories.

[@M0T0bri]

Definitely some of the best content on KZbin, thanks!

[@ericalger5003]

TGIW!! My favorite day of the week!

[@colinthomasson3948]

that all resonates with me most delightfully, as usual, thank you both for such lovely harmonies

[@mikeandrews1899]

Please expand 🤔

[@macmorgan6685]

My first experience with 2stroke engines was with Clinton A400/490 kart engines a later McCulloch MC10. The performance exhaust for the Clinton was a short megaphone the had a rather pop-pop sound. The MC10s pipe wasn’t much better and It wasn’t until I bought a Yamaha YDS2 with TD1 expansion chambers that I experienced the performance gains. In the early 80s I was racing a RD400 in WERA and bought a set of Erv Kanemoto’s pipes from Stuart Toomy that I saw the real gains in power.

[@farreltucker7466]

There is a good bit of information on those supercharged 2 strokes of the 30`s. They made a lot of power, but what that I found amazing was that these builders engines made even more power after the expansion chamber came into play. But without supercharging, they were banned anyway. Great stuff, I`m really glad that you guys came up with this. I always enjoy what you do. Thanks again.

[@denislemelin7653]

Great stuff, the tech and the older riders up to present just great stuff.

[@whalesong999]

Hail the Adler twins of the late '50s. Had expansion chambers from the factory and no other 250 could touch them for power. Only drawback for scrambles was the engine width and the pipes clearance under the engine. Hit he straights and you could whiz by the others. My first motorcycle ride was on an Allstate (Puch) 175 'split single' which I helped the owner decarbonize in our high school youth. It was pretty healthy running and well crafted little machine. I got to race my Adler once and won, TT scrambles. Next practice session, one lower end seized and that ended trying to compete on it though I did get it repaired and back running. Those bronze roller cages for the rod bearings held heat, also a problem on some early Yamaha twins that would hold heat on the dynamo side rod throw.

[@OldPhart-222]

Nothing like the aroma of Klotz in the morning. I still chuckle thinking about folks (young and old alike) coming into the shop telling fantastic stories about their XYZ 250 that "had a powerband in it." I guess you had to split the cases to replace a toasted powerband, devious little devils to find. I marked the wrapper on some clutch plates as "RD350 powerband" and left them on the counter. Lead to some interesting exchages.

[@gentjim5007]

Snowmobiles have always been on the cutting edge of 2 stroke engine performance. Their multi cylinder engines could be run with either a single pipe for a twin for economy models or twin pipes for more performance. And they always had big aftermarket support. Add a cvt to the mix, and building pipes for different applications becomes a black art. Love my 2 stroke sleds!

[@mmholling87]

Do they still make two stroke sleds? I'm a southerner thinking about moving up north.

[@connor3288]

A snowmobile 2 stroke with cvt in a lightweight bike would have explosive performance. I recall a custom racing bike a guy made, it had a gearbox, I think almost 200hp and under 300lbs I think!😯

[@robertryan2228]

Great stuff guys, I tune and ride watercraft (yamaha's) and the 4 strokes are amazing but I still have two strokes because of the fun characteristics and great tunimg potential, I used to build motocross two strokes for customers and always loved the sound. When I rode enduro I found 2t 250's the best all round weapon.. light and powerful! Keep up the great work.

[@ToddWright2]

I love Kevin's wry wit.

[@davidgreenfield2329]

What a great series oinformation exchange. Thank you.

[@markdixon4912]

I love these conversations, there so informative, kinda surprised I did not hear anything on secondary harmonics. But the design of the cosworth and Ducati valve train was brilliant .

[@paulmolino7455]

Another great info show. Fantastic !

[@ToddWright2]

I talked to Jan Thiel about the development of the Aprilia RSA125. Very instructive.

[@hmlc1130]

These talks are marvelous! Greetings from old Portugal.👌

[@SSV-i-c-e]

Great video two strokes always a win.i have a Suzuki rg150 here in New Zealand only built in Thailand or Thailand but they brought 100 here.38hp out of 150cc factory expansion chamber fun little bike good for over 100mph bit fragile tho.hi from New Zealand 🇳🇿

[@tonytoll6018]

Fascinating, thank you for sharing your knowledge.

[@Houseworksaws]

What a wonderful discussion/lesson. Thank you

[@jamessharp9790]

Great content. I dig all the two stroke technical stuff.

[@ClassicTrialsChannel]

Love the sound of a resonating expansion chamber. Loved the late 70s n 80s. i was the guy that friends came to when they wanted more power out there two strokes.

[@robert-wr6md]

Looking forward to the 6 cylinder edition Kevin.

[@robertrishel3685]

Glorious. Thank you for every word!

[@EwenNicolson]

Great chat.

[@selmtron]

I would love to hear you guys talk more about dynamic expansion chambers and resonators. Did the power valve kinda make them obsolete? Curious what designs were tried - cones on sliders inside the expansion chamber? Iris baffles? Hinged gates? Do we have to rebuild the exhaust after each race, now? How would you mecanically connect to the rpm? Fascinating! Lots of CVTs at the apex of 2stroke power, now.

[@jeremywalters2205]

Awesome ❤thanks guy's!

[@copperaudio9664]

Mark we slept on many rocks as well after the grassy infield at Laguna Seca was closed off. Many great years of motorcycle racing there in the 80's. We even got to do flags in turn 4 (old track) on a Friday practice once. I think that was the year Kenny and Randy did the wheelie show during the race. Ring ding ding ding!

[@mikeskidmore6754]

Seems I heard that Suzuki shipped a CZ Motocross bike back to Japan in order to get ideas how to build their First competitive two stroke Motocross bikes. Seems there was a Young man that was trained in Two Stroke Engineering in Sweden that got hired by Kohler in the USA to design some very competitive two stroke race Moters. Olev Aan had been building pipes and porting two strokes for various racers in Sweden. I think he went to an Engineering College in ND then got hired by Johnson Outboards and worked his way up to head Engineer in the Snowmobile race Department. After Johnson quit making sleds he started his own High Performance CO Building Expansion chambers clutch kits and he even built a V-4 Two Stroke Drag race Motor. He used to write articles for a Snowmobile Magazine . As a young man he raced oval track sleds and later had his own Aaen Performance race team ect. He wrote a book on setting up CVT Transmissions.

[@yorkchris10]

As a kid it was real mystery as to why the exhaust looked different on various two strokes. The pipes on dad's two stroke Suzuki twin didn't look much different than a four stroke. Our trail bikes had expansion chambers quite a ways back from the head and were that gave clearance for heat shield and leg. I remember an article on the Honda six cylinder race bikes. There was something unusual about the weight of components that varied from the center of the engine. I wish I could remember what it was, but you'd be surprised at what length they would go to to get equilibrium?/performance?.

[@carolinemcnabb9957]

Wonderfull as usual many thanks Germany's Lanz Bulldog tractors which are hot bulb single cyl oil burning two stroke engines had expansion chamber exhaust in the 1920s .Britian's Field Marshall tractors did this as well

[@YouCantSawSawdust]

@ 5:00,.."He was frightened by the violence of this thing,...". I thought Kevin was still referring to Otto's wife.

[@adawgz8290]

Two GOATs!

[@parisrogiest9324]

Talking about mapping and smooth pickup, might be interesting to talk about factory fuel injection systems (history). Having always driven 90S sportsbikes for 30 years my first injection model was a 04 Triumph speed4 and now a 23 Honda hornet... both have horrible clunky pickup out of the corner making me yearn for carbs again. Emissions being the main culprit, but would make an interesting topic.

[@GWAYGWAY1]

I am in the UK, in 1968 I bought a T20 Suzuki and on the road it was unable to cruise easily at 70 as the torque was too low. When it was run in I started to race it and wrote to US Suzuki and they sent me a copy of their tuning tips which I followed using the pipes they designed and it was quite good but unable to ride with the new Yamahas the TD2 in the dry but in the wet I had so much less sudden power that I could get faster times than the ‘hot boys’ . The pipes I had made were too long and had to be shortened to meet the rules and I read somewhere about pipes having the stinger place right inside the main body to the start of the converging point. It worked very well dropping the nasty noise but leaving the power at a reasonable point. I was poor and the bike would seize up as the points were always allowing timing changes, electronic ignition started then but were too much for me to buy.. I did well and even led major races until it blew up from preignition. I gave up as the money was just not there for me on £20 per week wages to keep going. Had I been able to get my TZR250 I bought for a road bike ,had been there I would have been a successful back then.

[@duc06820]

I built an H2 powered RD400 in 1996. It was more fun than my 98 R1.

[@FeatheredDino]

Interestingly enough, expansion chambers also work n 4 strokes -- and we are seeing that with 250 and 450cc race dirt bikes coming from the factory. Basically every brand has a long, curling head pipe that opens up to an expansion chamber. Now the expansion chamber on the 4 strokes is notcisbly different -- very different in fact, but it is, in basic principle and function, still an expansion chamber.

[@garyalexander2480]

It’s not a nightmare to control the throttle off the apex that’s what we all fell in love with it’s precisely the reason I like riding and racing it’s in essence the whole point when taming a motorcycle with variables changing constantly

[@randytolle6706]

The Name "Cotton" came to mind recently. I group Greeves, Dot and Cotton together for some reason.

[@markbrown-us4xe]

Feels like another ride on the magic bus. Where is the storage unit that Kevin keeps his brain ?

[@markj6049]

I just saw Krankit's video om the Honda EXP-2. I would love to hear Kevins thoughts om that bike 😊

[@vintagetrikesandquads4012]

I like the power delivery of 2 strokes more than 4 strokes. 2 stokes are more exciting, especially when they're on the pipe. The power is surging and violent. They are also more challenging to ride than 4 strokes--they aren't as forgiving--but that's part of the fun.

[@MikeBaca-rs8ij]

I had purchased a yammahq lt3 induro 100 I loved it a friend of mine had 1972 he had purchased abassa I expansion chamber his parents told him it was to loud they might make him get rid of his bike he traded me for my stock pipe the difference in performance was substantial I would race it at the local mx track and it was competitive

[@rolandotillit2867]

You can also change squish by changing the piston crown.

[@ralphwatten2426]

And...the RZ350! Now we can talk about reverse cone megaphones on 4 strokes. How important was it to know what the temperature of your expansion chamber is? I've seen thermometers on both dirt bikes and road track bikes with expansion chambers.

[@70sport37]

I made a parobolic defectlor that was adjustable in my old Tm 400 pipe and had good results . If it’s ever a thing it was my idea .

[@josephreisinger33]

I'll ask again about the XR650L but do you know about the back of my RD350'S shop manual there was a section labeled performance where it shows measur the ports in the cylinder and translate that to the cones of the expansion chamber?

[@johnsolimine1164]

Yamaha vs. Aremacchi (H.D.) happened in late 1974. That year, Roberts passed me on the Ontario straightaway like I was stopped. It was the year of the new 25 engine rule.... which lead to the demise of the lightweight class

[@tedecker3792]

When I started racing karts in 1960 expansion chambers were not in use. Started seeing a few in 1965. When I started racing motorcycles in 68 expansion chambers were well established.

[@DrSmile81]

...and today we have classes like the 50cc Freetec Series where privateers pushing over 20hp on the rear wheel from a engine, which comes in street legal form at a whooping 2,4hp🙂

[@alanwarner8489]

How everyman trial & error was successful in the two stroke era was lost on me when I cut 1/2" off the stinger to mount a silencer and lost half of the power band on my DKW which I never found again.

[@matthewfredrickmfkrz1934]

Add a restriction between the pipe and silencer ideally where the convergent cone would come to a point

[@Justen1980]

Awesome history lesson! I enjoyed the German terminology, too, as I studied the language when I was young. For me the two-stroke will always be the late 70s enduro bikes we had when I was a kiddo (suzuki ts250, yamaha dt 125, and rt100 trailbike)

[@11fishee]

Dearly appreciate these series....I'm wondering if there is a diect way to communicate to Mr. Cameron and or you something this presentation has made me think of.......Thank you in advance....

[@jimrobcoyle]

This week it's "Psycher World podcast"...😊😅

[@cycleworld]

Usually it says Psycho World… Thank for the heads up!

[@cam3002]

Can the expansion chamber concept also apply to 4 strokes? I know that the pipe diameter and length can be tuned for RPM range but seems an expansion chamber would also apply. Just have not seen it done.

[@11fishee]

A KTM 3OO EXC or W is all a dirt biker needs or, more importantly, use..... I love my 05. ..

[@Justen1980]

KTM needs to start making a 500cc two stroke dirt bike just for the bragging rights!

[@ricatiman]

Back in the late 60's I started racing flat track on Bultaco's 2 stroke singles... In the following years, as my skills improved and I was looking for more power, we went through a lot of porting experiments, and tried several pipes looking for the perfect one, and found they don't exist! We had ever narrowing powerbands in the wrong place of the powerband... After a couple of years, we realized that 2 strokes require rigorous testing, and rebuilding, trying to make more power than was wise. The extreme engines were too peaky to be useful on the dirt tracks. I started riding enduros and cross country in the 70's on great Yamaha and Husky bikes with stock pipes.

[@jpmorgen5726]

And at the end the Aprilia 125 GP road racers made 50+ HP at the rear wheel!

[@mikebuford5229]

Beyond Clever - How Two Stroke Exhaust Pipes Really Work @: kzbin.info/www/bejne/mXWmloKgfbaNqa8: Here's a clear illustration of how "Acoustic Supercharging" works. Enjoy

[@mikeskidmore6754]

Skidoo & Polaris both have 850 CC Two stroke twin Cylinder Two Stroke Snowmobiles with Turbos on them. The Skidoo has Direct injection and water/Methanol injection for longer hard pulls to keep things cool with out the weight of a big after cooler. The Skidoo makes 180 HP at Sea Level and 180 HP at 10,000 feet all buy electronic controls on the waste gate. The Oil Injection is ECM controlled 100 to 1 at light power ratings and 40 to 1 or so at WOT.. 2025 is the Last year for Yamaha Snowmobiles with were an Arctic Cat Chassis with a 3 Cylinder 4 stroke Motor .. both Naturally Aspirated and turbo charged.. The Turbo motor has stronger rods and I think Forged Pistons.

[@realblakrawb]

Divergent cone plus convergent cone plus a couple timing variables equals sound pulse supercharger

[@christophercurry7410]

What is the best material for 2-stroke variable exhaust valves? I’ve seen stainless steel ones and am wondering if this is a viable option.

[@lesmontgomery6498]

Dr Gordon Blair Queens uni Belfast. Used specs fpr a tm 400 7500 rpm . After jetting was a well running engine. Would hook up and smoke most off the line on half miles. I have a plug from an rc 166 run at Mosport in 67. E 12 H

[@KenAustin-i4x]

until 1998, an American aftermarket piston manufacturer whose name started with a W had not bothered to figure out suitable metallurgy to prevent their piston swelling like a cake in the oven and gluing itself to the cylinder wall, even in 4 stroke engines ! they caused me much grief as an engine builder/machinist.

[@markpavletich747]

They’ve certainly got it right these days. Used many in road race two strokes with nothing but good results. Correct bore clearance and a good warmup help a lot. Very little wear in these pistons now.

[@Loco_Motives]

40:46 DRINK!

[@gordonborsboom7460]

3/4 of the way through and no mention of twins or triples with one expansion chamber. Surely a compromise, but it does do some good?

[@nickrider5220]

I know a man who might know something about that.....Kevin !

[@GS-zv3qn]

6 inline your doing fine

[@keelangerken5154]

What advantages and leaps 2 stroke technology made in the 90's and 2000's has been negated in recent years by 4 stroke technology now. Modern intake, head, header, and fueling/mapping designs have allowed modern 4 strokes to make the same specific power as 2 strokes have. Modern packaging, cad, and materials have allowed them to weigh the same. 2 strokes used to make a higher specific power due to the supercharging effect of the pipe to increase the displacement of air processed, of which modern intake path, cam overlap, and exhaust scavenging has now allowed 4 strokes to process more air than they displace as well. 2 strokes used to be considered higher hp per size due to a power stroke or pulse every tdc of the crankshaft, but with modern 4 stroke designs, a 250cc 4 stroke engine having a power pulse every other tdc of the piston at 14,000rpms, processing 300cc of air will be the same as a 2 stroke processing 300ccs of air every tdc at 7,000 rpm. AMA must realize this in order for 2 stroke rules and homologation to make since and further allow 2 stroke technology to increase. Currently, 2 stroke technology is Only advancing through dirt bikes. 4 stroke technology has been able to advance on every ICE front including car and truck motorsports.

[@KingBrolesław]

🏆🏍️

[@jamesclapp6940]

"being the pepe" is the key phrase!

[@rogerw3818]

I'm sorry, the combination of cake and two stroke so distracted me, I have to take a break.

[@wdhewson]

"Two strokes per stroke" for a steam engine is incorrect. I would offer that it is two strokes per cycle. Or perhaps called a 1-stroke engine. And one has to admire the efficiency of a locomotive engine where the connecting rod goes right to the wheels without intermediate losses.

[@bultacoracer7729]

This got so far of course. It was supposed to be about the design of tuned pipe not your old racer stories. Save those for beer drinking sessions in your garage

[@armandbarbe1812]

Ship's engines are high-power 2 strokes. They run at 85% MCR for weeks on end for a crossing, year after year, on oil as thick as tar. Not very clean though.

[@Guinnessisgoodforyou]

Mark if that tash gets any bigger you will look like Paul Teutul snr lol, excellent episode as usual spoiled by an annoying misfire called add breaks, omg it was terrible, much worse the other episodes, makes me want to invest in the add free version of KZbin. Brian from Scotland.

[@bloodspartan300]

Now explain why 4 stroke dont have it??

[@davidebbs6146]

Two stroke technology has hardly evolved in fifty years or more, it is a ‘blind alley’ that has absolute no escape. Environmental concerns have killed it.

[@68orangecrate26]

Yeah… Interrupted by a IPhone 16 infomercial… Just great! The LAST THING I’M NOW GOING TO GET IS A iPhone 16. Ridiculous….🤨

[@rodwetmore433]

It is not an acoustic wave, but an pressure wave traveling much faster (5000'/sec) than an acoustic wave (approximately 1000'/sec).

[@mikeskidmore6754]

Reparations The Germans had to give up the Blueprints of the DKW Motorcycle to other Counties to Copy.,

[@fendermarshallbluesbox3407]

in Holland there is some law, that allows chemical waste to be mixed with ship diesel fuel 😂😂, not kidding. no two stroke in moto gp ? lets ban every sport, so people dont travel by plane or car

[@clayz1]

Kevin should be knighted, but he lives in the USA not the UK. *hic* 🎉 happy new year everyone except Putin

[@MatsModén]

It come from east germany MZ engine ! And was stolen later by Japanese ! Exspanion camber.

[@Trevorpartington-yc6ri]

I dont have kids , could care less about the enviorment .................. Please PLEASE ! bring back two strokes !

[@Loco_Motives]

55:50 DRINK!