2stroke, higher revs are better for it?

[KevlarPants]

Quick question, my instructor told me a while back that 2 strokes 'prefer' to be run at higher revs. This, he explained, was due to the way that the reed valves operate. So, higher revs allows them to open up properly, clearing out any crap that may have accumulated.

Or something like that.

Fact or fiction?

[silent]

im inclined to agree to a degree but they MUST be warmed up properly before being reved hard and as always the more revs the shorter the mileage the engine is going to do

andy

[Kickstart]

Hi

Not so sure on the reed valves being a part of it. More down to (in my view) inefficiencies in drawing the mixture through the crank cases leaving a fair amount of fuel on the insides of the engine. These will then be sucked in as larger drops of fuel and are not going to burn as well.

All the best

Keith
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[gavin]

depends on what revs its tuned for! the stuff about reeds is nonsense, they open from the tip, at very low suction, high revs or low revs, makes no difference.


in my experience, all engines, 2t or 4t, prefer to be driven rather than abused. revving into the red is a form of abuse, but so is crawling around in a high gear at low revs all the time.

[alains]

well it's not completly non-sens , but what is missing is : what about the exhaust valves ?
the best ratio of a 2 strokes comes with a good balance between intake and exhaust . it's a question of mixture speed . when the plug burn the mixture and push down the piston it's needed that the burn mixture slow down the fresh mixture entering the carter and the barrel , otherwise a part of fresh mixture goes out with the burn one . more you run quickly and more the time from intake to exhaust shortening . but if you have no intake reeds , part of the fresh mixture will flow back. at low revs you need a system to slow down the exiting mixture (exhaust valves) and when you go up you need to have a free exit . i am not engineer , but it has been calculated and i remember having seen that on the workshop book for the suzuki 125 GT (1974) . a doctoral thesis from a young german about exhaust and intake system was edited in the middle of this book . the testing of different exhausts was made in race on a KREIDLER 50cc
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[the grim reaper]

The reason behind the revving of 2-strokes is based on how the engine deals with the emissions of cumbustion. I have seen a 2-stroke that was crawled around all it's like and it was a right mess, coked up to hell. The reason is that a 2-stroke doesn't have valves like a 4-stroke, this means that there isn't an empty chamber for the fuel/air mixture to move into (from below the piston). This system works better at higher revs for two reasons, firstly, the fuel/air mixture is being forced into the chamber faster by a faster moving piston which mixes the fuel/air better and, secondly, this then clears the combustion emissions better. Low revs leaves the combustion by-products to build up on the piston crown and in the exhaust.

It is right that you should warm the bike up well before revving it though.

Cheers

Grim
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