Kawi2strokes.com Forum

Come on John, you know this:- The harshness of the cackle is due to the ex port top edge being flatter (and wide) meaning that it opens and closes all at once quite suddenly. For street motors it is curved for the two fold benefit of a softer note and being easier on ring wear.
I might be dreaming this bit, but didn't some later street motors even have a small vertical channel added to the top of the port to help make them quieter, with this groove/channel not being large enough to affect the effective port timing of the main port window?

Yes.

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"One day, your life will flash before your eyes. Make sure it's worth watching." : anon.

In laments terms, they sound this way because they are so full of ausome....It has no were to go but out the pipe and what you are hearing Is ausome in the form of a sound wave....
Thus creating a glorious melody..

Cool

They both contribute Hal. As a motor with the same top radius will sound more "cackly" with more duration. I didn't want to get into "flatter" exhaust port roofs, as then some "might" think that's a good thing to do, and start tearing out rings. It takes some complex work, to make it work.

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

No Hal, you are not dreaming. This design was developed first time 20 years ago by Stihl for their chain saws in order to get them quieter. I have seen the dyno charts - there wasn't a big loss in terms of power, but the noise level was much lower.

Late to the post party, (Mr. low tech here); but do we hear some of the cool pops thru the intake ports/air cleaner(s) as well? I once heard "2 strokes drink a lotta air", although a 4 cycle turning 16,000 rpm probably sucks a lot (ha, ha)?

A 2 stroke 250 will "theoretically" pull tyhe same air at 8,000 as a 250 4 stroke will at 16,000. That's a lot of "WWWWWWWWAAAAAAAAAAA".

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Twist the throttle, tilt the horizon, and have a great time. What triples are all about...........

Don't forget, chainsaw exhausts are not usually expansion chambers so the "softening" of the exhaust pulse will have little effect on power output. However, a 2 stroke equipped with chambers the sharper the "crack" the better.

J

In general yes - but in this case: nope! General statements are risky if the work which has been done is unknown.

I knew I had a copy - now I've found it. Here is an example about the exhaust port modifications in terms of noise development (the inlet port has been studied as well):



The whole development was done between 1980 and 1983!