Expansion chamber info.

[A.Holley]

I apologise in advance for going slightly off topic here, but I figured someone here might have the info I am after.
I am in the process of acquiring a 1958 Jawa 250 single. Now these are a bit unusual in having a single cylinder with twin exhaust ports and pipes.
Because of this, they have 2 seperate pipes and mufflers.
The intention is to do what the factory did, and convert the std road bike into a ISDT replica.
As it doesn't currently have any mufflers, I want to fit twin expansion chambers, which the factory also did.
Does anyone have any clues as to how to design a pair of chambers that are fed by a single cylinder?
I actually seem to remember that Suzuki did the same thing in the early 60's with one of their early motocrossers.
I have most of the books by Jennings, Bell , Blair etc and none of them go into this subject.
Any help you can give will be muchly appreciated.

Regards
Andrew Holley

[Jimroid]

I would think an immediate Y pipe as short as possible, and than normal chambers using half the engine displacement for figuring chamber dimensions.

[tz375]

Agreed in principle. Either Y pipe both into one pipe or use half the recommended design cross sectional areas. If you input half the stroke into the software it will calculate the wrong length. I would try to design it as if it had a single pipe and use the recommended angles which will yield cross sectional areas of half but not half the diameter. Area of a circle is Pie * 'd' squared/4.

[Jimroid]

I'd like to see a picture of that exhaust port. If it is two completely seperate ports that would make it even easier.

[tz375]

Is it this one?

http://cybermotorcycle.com/gallery/jawa ... s-S553.htm" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Appears that they fly....
http://vroum52.com/isdt.img/moto-CZ-ISD ... vaquie.jpg" onclick="window.open(this.href);return false;

[A.Holley]

They do have 2 seperate exhaust ports, with a divider between them.
I intend To do a little work on the motor, nothing drastic as I want to retain its broad power band.
Peak power on the factory ISDT bikes was only about 21hp at a heady 5000 rpm.

The colour pic that was posted is pretty much the look I am after except for those big heavy std mufflers. Some got fitted with simple single stage diffuser chambers, so want to stick with that type as a multi stage pipe would not look right on something of this vintage.

I am rather looking forward to having a bike built the same year I was born (1958).

Andrew

[joolstacho]

Andrew, if you want to get anything NEAR that bhp you're going to need to do extensive tuning!
I recently gave away one of these bikes (mine was a Russian one, badge engineered). Built like a tank, and just as heavy !!! Good luck.
(Sorry to rain on the parade!)