503 and 582 engines

[Slider]

I’m reading a very interesting book on tuning a 2 stroke motor. Its scary to see how it works. If you take a 503 or 582 motors, 1 x exhaust, it doesn’t make sense that it will work. Why don’t they use 2 x expansion boxes on these motors. I know that it will add weight to them, but if you look at the operation of the exhaust, with the positive pulse, pushing fuel back into the piston before it closes, it can only work better with 2 exhausts. Am i missing something?

I tried to put a "moving image" on this forum, but this forum cant take it.

[John Boucher]

Kaplaks...

You are correct. Look at Kork Ballingon's KR500 and all the 2-stroke GP bikes. I used to build expansion boxes with some intricate formulas using rev range, powerband width, exhaust port timing, length and diameter! Used taper headerpipes etc.
There was a video link on youtube posted by someone which shwed a ROTAX with expansion boxes. Lekker HP and sounded good.

Used to ride an RD350LC which embarassed many a 750 SB in its time!

I think there are companies in the USA that build high performance pipes for the Rotax range - eg. taking a 582 up to the 100hp range. Well, not so far fetched as it's sibling (583) is a 100hp plus motor in the Skidoos

[Morph]

However, I would think a hotter exhaust detracts from the reliability of the engine. IMHO

Additionally the hotter exhaust will also allow you to push beyond 6800 rpm, that now has gearbox ratio implications and prop length limitations to consider

I am moving this to the Technical Forum

[John Boucher]

I agree Morph...

One always wants that margin of reliability. Tuning a 2 stroke for hp or as any engine beyond it's design capability contribues to the decline of it's longevity

[MADDOG]

Additionally the hotter exhaust will also allow you to push beyond 6800 rpm

You can tune the pipe lenth to keep the power down below 6800 rpm and control the heat build build up, but alas you cannot control the CAA and your AP will not do the work for you. So we must dream on.

[John Boucher]

Each section of a tuned pipe has a funtion and an important one at that.

From controlling maximum revs, powerband (and no, you don't buy these at your local bike shop) inception and revrange to peak off!

It also just helps the machine to breath better and yes also cools the engine better by disposing burnt fuel & gases and assisting in unduction due to sonic pulses.... Seriously not just 2 cones and a cylinder welded together!

The advent of pipes was seriously used on marine motors in the USA when they were used for racing.... Bikes were still using 4-strokes back then!

[John Boucher]

Here is some serious software : http://tsrsoftware.com/newpipe.htm

I will have to look for public domain formulas as I have put mine to rest some 23 years ago!