Engine evolution?

[crash harry]

2-strokes are being phased out for percieved green reasons, no doubt about it. Visible smoke = emissions in some people's minds. Most green issues are similarly clouded by emotion and conveniently devoid of science.

There has been a lot of interesting work done on the 2-stroke engine which sadly may never see commercial use. Someone (I think Renault?) was working on eliminating the transfer chamber by using a supercharger to generate transfer pressure. It's been done before in opposed piston engines, but I haven't heard of this configuration being used in a conventional single-piston-per-cylinder 2-stroke. It could be interesting, especailly when combined with direct injection. Big advantage is a 2-stroke engine with no oil in the fuel and conventionally lubricated rotating assembly.

It's possible that such an engine could use poppet valves, like a 4-stroke, just with different cam profiles. Using the Vtec idea with 2 sets of cams that are activated as and when required, it may be possible to have an engine that can run in 2 or 4-strke configuration depending on power/efficiency requirements. Now THAT would be cool.

(spot the engineer with too much time on his hands...)

[fridayflash]

emissions emissions emissions,california emission control
laws certainly sounded the death knell for two strokes in
offroad racing,and prompted advances in 4stroke development
in dirtbikes [california being the biggest market for mx and enduro
bikes].most obvious example of this development is the yamaha
yz/wr engine,which when released in '98 sporting 5valve head
and over square dimensions was truly ground breaking

p.s great 1st thread

[Mental Trousers]

I think the main reasons for change from 2 stroke to 4. Was for similar reasons Formular one changed their engines from V 10's to V8's. Reduce costs to build and slow the buggers DOWN. (make them SAFER)

Safer yes, but a 4 stroke cheaper than a 2 stroke?? Not ever.

.... mind stream ....

Believe it or not they've all been done and are out there, in production somewhere (although the poppet valves one is extremely rare as it adds complication to what is a simple engine).

[slofox]

Was the Q related to racing or general bikes?

Was interested in racing bikes........

Interesting posts everyone - thanks for the discussion. Confirms a few rumours I did hear out there........

[Motu]

emissions emissions emissions,california emission control
laws certainly sounded the death knell for two strokes most obvious example of this development is the yamaha
yz/wr engine,which when released in '98 sporting 5valve head
and over square dimensions was truly ground breaking

The turn around for 4 strokes was the Husky 510 when it won the premier MX open championship.This was a lightweight 4 stroke with a 2 stroke bottom end (no oil pump).Yamaha springboarded off that development and got the concept to the masses....like who would ever buy a 510 Husky?

In road racing WSB was far more popular than GP racing as the competition was so close and the bikes had a link to what the spectators rode.500GP was like watching the 250 or 125 class - just screaming 2 strokes that bore no relationship to what was available on the showroom floor.MotoGP wanted to cash in on that and bring the viewing public back to the top class of motorcycle racing.As in MX they made the 4 strokes twice the size of the 2 strokes,and bent the rules in their favour.....then they practically banned the 2 stroke.

CC for cc,a 2 stroke will clean up a 4 stroke,anywhere,anytime.

[Ocean1]

The great unwashed ar just too conservative to buy anything really different. There's more off-the-wall designs out there that never see the light of commercial day than most hear about.

Some of 'em are really cute. http://kugelmotor.peraves.ch/

[Forest]

In general terms, the bike manufacturers basically make what their customers want to buy.

Their customers don't want two-strokes.

[2Cycle]

If any of the major brands bought out a new DI two stroke street bike I'm sure it would sell well enough to make it viable.

I had my last bike (rg150) for ten years. Because there was no new larger/mid size 2 stroke to replace it with, I had to go 4 stroke. Customers have no choice. Manufacturers are not even making concept 2 stroke bikes to test public reaction. So it is not fair to assume that noone wants one.

[pete376403]

Someone (I think Renault?) was working on eliminating the transfer chamber by using a supercharger to generate transfer pressure. It's been done before in opposed piston engines, but I haven't heard of this configuration being used in a conventional single-piston-per-cylinder 2-stroke. It could be interesting, especailly when combined with direct injection. Big advantage is a 2-stroke engine with no oil in the fuel and conventionally lubricated rotating assembly.

It's possible that such an engine could use poppet valves, like a 4-stroke, just with different cam profiles. Using the Vtec idea with 2 sets of cams that are activated as and when required, it may be possible to have an engine that can run in 2 or 4-strke configuration depending on power/efficiency requirements. Now THAT would be cool.

(spot the engineer with too much time on his hands...)

Sounds like a pretty good description of the Uniflow two stroke diesel, of which there are bazillions in operation (GM, Nissan UD to name a couple)

[glice]

Can't argue with that.

Direct Injection is definitely way more reliable and usable now. But it's too late. Now it's going into things like Scooters and outboards, but not bikes. None of the manufacturers can see a market for 2 strokes bikes at the moment. Blame the Greenies and all the misconceptions and misinformation around.

ktm is doing it, or about to. they are the only bike manufacturers still developing the 2 stroke from what I've heard.

[scumdog]

Possibly piston/ring life (or lack of it) in a 2-stroke is off-putting to some??

[CookMySock]

modern supercharged four-strokes are the future ;

http://youtube.com/watch?v=YF0SCxIQ6PU

DB

[geoffm]

Possibly piston/ring life (or lack of it) in a 2-stroke is off-putting to some??

What are the service intervals for these 4T MX bikes? 10 hours springs to mind - they are certainly short and the rebuild costs against new rings in a 2T motor are much, much higher, especially if the 2 stroke has o-ringed heads.
G

[henry]

... Reduce costs to build and slow the buggers DOWN. (make them SAFER)

2 Strokes are significantly cheaper to develop, build and maintain than 4 strokes which is the reason for all the fucking about with the 250 GP class. If they make it 4 stroke no one will be able to afford to compete.

[henry]

Their customers don't want two-strokes.

Bollocks..