The ULTIMATE 2-stroke bike engine

[speedpro]

OK - this isn't intended as a thread about a bucket engine but "Buckets" seems a good place for it considering who regularly posts here.

I've been thinking what the ultimate 2T engine would be unencumbered by any rules and restrictions. Huge marine diesels are very efficient but don't actually make much power considering their size. An RS125 makes lots of power but efficiency is down. There are direct injected engines in outboards, scooters and snowmobiles. But given a few very basic criteria like it has to fit in a bike and has to run on petrol, what would the engine be.

My thoughts were possibly a twin, parallel, tandem, or probably V. About 500cc, forced induction, 4 valve heads solely for exhaust, fuel injected directly into the intake passages. The intake passages would be straight and of a tuned length, or not, directed into the cylinder at the optimum angle and fed from a pressurised annulus. The cylinders would be phased to fire 180deg apart to even out the load on the supercharger and the demands on the intake plenum.

Transmission wise I don't see why more bikes don't use a CVT style transmission. Not a basic scooter version but something like that used in high performance snowmobiles. A 4-stroke style plain bearing bottom end could be used but then there would be issues with piston length and sealing intakes to crankcase.

I'm just curious what other people think would be the engine configuration given very few rules. I'm trying to think of something for TZ to get into before he gets too old that would be interesting and push boundaries a bit.

[richban]

Transmission wise I don't see why more bikes don't use a CVT style transmission. Not a basic scooter version but something like that used in high performance snowmobiles. A 4-stroke style plain bearing bottom end could be used but then there would be issues with piston length and sealing intakes to crankcase.


You would have to ride it very differently from a normal transmission. The breaks would have to be something special to ride it fast. I remember racing an auto scooter you had to use the rear break a lot to turn it in. I would go for a conventional transmission. Would be good to see a mad project on the go.

[Buddha#81]

OK - this isn't intended as a thread about a bucket engine but "Buckets" seems a good place for it considering who regularly posts here.

I've been thinking what the ultimate 2T engine would be unencumbered by any rules and restrictions. Huge marine diesels are very efficient but don't actually make much power considering their size. An RS125 makes lots of power but efficiency is down. There are direct injected engines in outboards, scooters and snowmobiles. But given a few very basic criteria like it has to fit in a bike and has to run on petrol, what would the engine be.

My thoughts were possibly a twin, parallel, tandem, or probably V. About 500cc, forced induction, 4 valve heads solely for exhaust, fuel injected directly into the intake passages. The intake passages would be straight and of a tuned length, or not, directed into the cylinder at the optimum angle and fed from a pressurised annulus. The cylinders would be phased to fire 180deg apart to even out the load on the supercharger and the demands on the intake plenum.

Transmission wise I don't see why more bikes don't use a CVT style transmission. Not a basic scooter version but something like that used in high performance snowmobiles. A 4-stroke style plain bearing bottom end could be used but then there would be issues with piston length and sealing intakes to crankcase.

I'm just curious what other people think would be the engine configuration given very few rules. I'm trying to think of something for TZ to get into before he gets too old that would be interesting and push boundaries a bit.

sounds like a jetski or snowmobile:wacko:

[quallman1234]

An RS125 makes lots of power but efficiency is down.

RS125 For the win! It depends what you mean by effciency, if you mean power to displacement efficiency then the RS is great!
If you mean fuel efficiency, your'll be surpised. My RS gets roughly 10kms/litre not actually that bad. (Based on 300ml's per lap at manfield)

[Deano]

RS125 For the win! It depends what you mean by effciency, if you mean power to displacement efficiency then the RS is great!
If you mean fuel efficiency, your'll be surpised. My RS gets roughly 10kms/litre not actually that bad. (Based on 300ml's per lap at manfield)

Nah bro - you'd spend all race day working on it ;)

[avgas]

CVT - sorry but you need every gear you have on a 2 stroke. Its to do with the fact that all the good ones have the most nonlinear power curves on the planet. The only way I can see CVT working is on a track like NASCAR.

As for the engine. I really like a lumpy single smoker. Something special about that sound and the way you ride it. Feels more real, like if you get it wrong the whole engine stops.
But one day I want to chuck a Yamaha 2t outboard in a bike frame just for fun.

[speedpro]

Would be good to see a mad project on the go.

That's what I'm thinking, not putting a blower on an existing engine and just making it "more". Jetskis and snowmobiles are conventional 2-strokes and all very normal though they certainly have the goods. I'm asking if anyone knows if a supercharged 2-stroke built solely as a supercharged engine, not a modified normally aspirated engine, would be better than what are admittedly good modern conventional designs. Development of supercharged 2T engines in racing was killed off before they really got sorted. With modern designs and materials would/could they be better in any way. Turbo or supercharged 4T engines have advantages and I'm thinking a purpose built 2T forced induction engine would also have advantages. But what form would it take to most benefit from the supercharging? If you could head off in the efficiency direction of the big marine diesels but in a smaller high revving package you'd have to be on a winner.

As for CVTs, how many gears do you need? A CVT has infinitely variable ratios. With careful tuning of weights and ramps they will match most engines nicely.

[jasonu]

CVT - sorry but you need every gear you have on a 2 stroke. Its to do with the fact that all the good ones have the most nonlinear power curves on the planet. The only way I can see CVT working is on a track like NASCAR.


Snow mobiles do very nicely with CVT transmissions.

[koba]

Such a machine may be eligible for land speed records.

I've also had much thoughts about the 4 valve head used for exhaust and the annular entry inlet ports. Maybe one could use a massive turbo housing wrapped around a barrel. (on a single or maybe a V-twin.)
I believe such designs have been used and are very efficient in their application but I'm not sure how they would work at the revs that would probably be needed to make high power levels per cc. (if that's the goal)

[TZ350]

Development of supercharged 2T engines in racing was killed off before they really got sorted. With modern designs and materials ...... I'm thinking a purpose built 2T forced induction engine would also have advantages. As for CVTs, how many gears do you need? A CVT has infinitely variable ratios. With careful tuning of weights and ramps they will match most engines nicely.

Supercharging, CVT, and the Orbital fuel injection and engine management system could be would be worth having.

[speedpro]

A large turbo compressor housing fitted around a barrel is an idea but the airflow "around" the cylinder would probably continue through the ports to inside the cylinder. That might actually be a good thing depending on how the scavenge flow worked. I was thinking more of the ports and ducts being like a conventional setup but the ducts would be straight, possibly of a tuned length, and fed from a plenum which extended around the cylinder. The plenum being pressurised. Fuel would be injected only after the exhaust valves closed. Looking from above the cylinder the port ducts would resemble fat spokes of a wheel and the annular plenum would be the tyre.

If a 4T type bottom end was used an oil control ring would be needed at the base of the piston. With either bottom end, lubrication of the piston would be a problem with the mixture entering the cylinder directly through the port ducts. I must have a look at an OCP engine.

I type too slow

[speedpro]

The OCP has a total loss lubrication system and looks to inject oil immediately before the reed valves which feed the crankcase. The crankshaft seems to have been drawn with a boltup big end on the rod. Apart from the fuel injection and the very good oil injection system the OCP engine looks remarkably "normal".

Maybe just a small amount of regular 2T oil injected into the mains and left to lubricate the cylinder like normal would be OK. There wouldn't be the flow of air through the crankcase on my idea of a forced induction 2T engine so it wouldn't need the quantities of oil like a standard high performance engine. With a common crankcase for a twin firing every 180degrees any volume displaced by the downward travelling piston would be made available by the other piston which would be travelling up so there would be little crankcase pressure fluctuation, only air and oil mist moving back and forth. A flat twin with a single crankpin would be simple, apart from trying to smooth it out.

Maybe a twin crank, 90degree v-twin, with a common crankcase volume. My head hurts even trying to visualise the forces to balance.

[Farmaken]

A large turbo compressor housing fitted around a barrel is an idea but the airflow "around" the cylinder would probably continue through the ports to inside the cylinder. That might actually be a good thing depending on how the scavenge flow worked. I was thinking more of the ports and ducts being like a conventional setup but the ducts would be straight, possibly of a tuned length, and fed from a plenum which extended around the cylinder. The plenum being pressurised. Fuel would be injected only after the exhaust valves closed. Looking from above the cylinder the port ducts would resemble fat spokes of a wheel and the annular plenum would be the tyre.

If a 4T type bottom end was used an oil control ring would be needed at the base of the piston. With either bottom end, lubrication of the piston would be a problem with the mixture entering the cylinder directly through the port ducts. I must have a look at an OCP engine.

I type too slow

Sounds very similar in concept to a Detroit Diesel engine as produced by the yanks.
Supercharger feeding the crankcase around the liners which have a spiral port arrangement about halfway along their length ( somewhere near the bottom of the stroke if memory serves )
Flat head with 4 Ex valves and injector in the centre of the valves .Combustion chamber in the piston crown.

Yes it is a 2T and they sound like they are screaming at 2500 rpm -- beautiful !!

[pete376403]

You are describing GM (Detroit), Nissan UD diesels, among others. Commer TS-3 and Napier Deltic use (used) some of your ideas but are more interesting due to opposed piston design (Commer TS-3 sound is beautiful)

[richban]

Snow mobiles do very nicely with CVT transmissions.

Yeah they do. But when you snap the throttle off they slow down fast due to heaps of drag on the show. Bikes will keep on rolling. And like I said you would need some very modular rear breaking to turn it in like a conventional gear boxed bike. Especially if it was a 200hp 500. Rolling into a corner at 260 with just that rear break to get it turned would be interesting.

CVT would be great if building a drag bike.

[Grumph]

Yeah they do. But when you snap the throttle off they slow down fast due to heaps of drag on the show. Bikes will keep on rolling. And like I said you would need some very modular rear breaking to turn it in like a conventional gear boxed bike. Especially if it was a 200hp 500. Rolling into a corner at 260 with just that rear break to get it turned would be interesting.

CVT would be great if building a drag bike.

Yeah, well slipper clutches are part and parcel of the drag world...For those interested in the CVT/racebike concept, google Monotrack Experimental and have a look - it's been done. From what i read elsewhere the stall speed of the cvt was high enough that in theory you'd never drop out of the power band. Think of it as a single gear with an automatically slipped clutch....
Like a lot of belt drives I understand it was let down by a lack of alternative ratios.
A combination of a cvt primary drive with a 3 or 4 speed dog box may work - but this is only an elaboration of the Chapparal CanAm car's "auto box" which was a torque converter driving a 2 speed dog box. This worked great in a light car with enormous torque....

[speedpro]

I've changed the final drive ratio on my scooter. The only time it's noticeable is where it used to top out at 105kmh it now goes off the clock plus a bit more. The roller weights working against the spring determine engine revs at any throttle position. Throttling off does result in the CVT immediately going to the highest gear ratio possible and therefore not much engine braking happening.

[speedpro]

More thought has been wasted on this. I've been thinking that regular port and ducts are all designed due to limitations caused by being fed from below the piston and the limitations of an air cooled barrel requiring the single exhaust duct to be at the front for cooling. The switch to water cooling was only taken advantage of by an extension of the power gained and by relocating the exhaust duct to another position other than the front. Designers stuck with the single exhaust duct on one side due to the scavenge pattern. If they'd thought about it and changed the scavenge pattern they could have utilised more exhaust ports/ducts.
Frits' FOS cylinder takes advantage of water cooling by having exhaust ports wherever he wanted them. Only made possible by his new scavenge pattern. Those 6 transfer ports could just as easily be fed by a circular plenum in turn fed by a supercharger. The truck engines have a similar arrangement but with poppet valves in the head, and a four stroke bottom end. For a
180-degree-firing-order V-twin with a shared crankcase you could run a regular 2-stroke bottom end.
The question for Frits is how well do his cylinders work? I can see the central column being formed by the intake streams but have difficulty seeing how the flow continues out the exhaust ports and doesn't form a circular rotating column - up the centre, out across the head, down the cylinder wall, to blend with the incoming streams and go round again.
Also in normally aspirated form I'd imagine all the time area values would be similar to regular cylinders but with big advantages in the port layouts to achieve it. Is there a way to determine requirements if the engine is supercharged or would it be a case of suck it and see?

[Tard]

Jeez, I hope F5 Dave's alright...:wait:

[Spearfish]

Jeez, I hope F5 Dave's alright...:wait:

He must be in a bad way, what ever it is.

[F5 Dave]

Well I had a bit of a hangover after wifey & I polished off some very nice wine last night, but I had a V & some cheese on toast to correct the grease imbalance that sometimes occurs and quite frankly I'm feeling pretty good now. I don't even think I'll need a kebab at lunchtime.

But thanks for thinking of me.

[avgas]

Snow mobiles do very nicely with CVT transmissions.
The first part of your sentence should tell you why. Incidentally the same reason you don't need gears on a wave runner/jetski. Traction vs Maneuverability.

Sadly unless your planning an 2-stroke drift bike, a 'chop down' is usually required every now and then.
I have used the CVT equivalent of a 'chop down' and was massively disappointed. CVT is too 'long' to for a proper 2-stroke chop-down to have any effect. Now a shot of NOS at the same time as the CVT travels down to a "faster ratio" could probably do it justice.

[Spearfish]

The first part of your sentence should tell you why. Incidentally the same reason you don't need gears on a wave runner/jetski. Traction vs Maneuverability.

Sadly unless your planning an 2-stroke drift bike, a 'chop down' is usually required every now and then.
I have used the CVT equivalent of a 'chop down' and was massively disappointed. CVT is too 'long' to for a proper 2-stroke chop-down to have any effect. Now a shot of NOS at the same time as the CVT travels down to a "faster ratio" could probably do it justice.

Has anyone ever made a manual cvt?
Instead of using weights and springs perhaps using another twist grip/rocker pedal with some sort of cam in the guts to manually move the pully up and down the ratios.

[avgas]

Has anyone ever made a manual cvt?
Instead of using weights and springs perhaps using another twist grip/rocker pedal with some sort of cam in the guts to manually move the pully up and down the ratios.
Hmmmmm would work on slow speeds. But if you want the cam to work its going to have to move at 10 times whatever the speed of the CVT pully runs at. And not only that its going to have to be all over the CVT pully.
It will look like a cone shaped tunnel boring machine when its finished.

[Yow Ling]

Has anyone ever made a manual cvt?
Instead of using weights and springs perhaps using another twist grip/rocker pedal with some sort of cam in the guts to manually move the pully up and down the ratios.

Aprillia do one on a 800cc thing, its pretend manual as there is a computer in there working the pulley to give steps. could be done with oilpressure and a feedback pot.

FWIW I quite like opposed piston 2 strokes, not like the double knocker TS3 more the Junkers type with geared cranks, really short stroke per crank , aysemetrical timing. Downside is maybe a bit tricky on petrol, but diesel is cool. Must surley be allowed 200 cc real diesel in buckets with forced scavenging as opposed to supercharging. maybe wobbly can do a Kadency pipe for the diesel

[F5 Dave]

Pity digital cameras were not popular a ways back. Mike (G) do you have any film of that Uniflow engined Bucket that was at the GP?

[speedpro]

Nope, but I've got video of it's 500cc big brother being fired up for the first time, somewhere.

[Sketchy_Racer]

Yeah they do. But when you snap the throttle off they slow down fast due to heaps of drag on the show. Bikes will keep on rolling. And like I said you would need some very modular rear breaking to turn it in like a conventional gear boxed bike. Especially if it was a 200hp 500. Rolling into a corner at 260 with just that rear break to get it turned would be interesting.

CVT would be great if building a drag bike.

For what it is worth,

On my latest GSX-R600 where we are running yoshimura engine managment, I have had the bike setup with a lot of anti engine breaking, as I hate it when I get compression lock when under hard brakes into a corner. The first time I rode it I almost ran off the track at the first turn as when you shut the throttle and expect it to slow down it damn feels like it speeds up! Just like a scooter!

However over time It has started to work very well in keeping the rear end of the bike stable under heavy braking, and I never use the rear brake, usually the rear brake does nothing as the wheel isn't touching the ground!

I would be keen on a CVT style gear system, and may even build one for the next project....

[pete376403]

Has anyone ever made a manual cvt?
Instead of using weights and springs perhaps using another twist grip/rocker pedal with some sort of cam in the guts to manually move the pully up and down the ratios.

Rudge did it back in the 1913 or thereabouts. They were banned from racing in the TT as it was deemed to give them an unfair advantage. From then on the rudge insignia was a five barred gate - playing on the barred from racing theme.

Google or Wiki "Rudge Multi"

Just about whatever you can think of has probably been done before

[speedpro]

There is some pretty high spec. CVT transmissions out there. Check these:

http://www.aaenperformance.com/snow_clutch_roller.asp

I'm sure they could be used on a motorcycle

[Asher]

http://www.youtube.com/watch?v=jQoY7ECyoN8

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