Exhausts on a parralel twin?

[Thom]

Im wanting to make a gs500 project as a show bike, or atleast as the gs500 project Mk.2.

Im wanting to better understand the exhausts.

Im going to have a Ti system knocked up.

Tha standard system has a cross over section about 6-10inches below the exhaust ports. Is this neccesary?

Or could i simply have two single exhausts made each a single unit for each of the two cylinders?

Also, is there any reason why an expansion chamber wouldnt improve the powerband on a 4 stroke? i dont really understand expansion chambers but would be interested in having one made if ti could make the bike a bit more lively.
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Current Bike: 1996 Yamaha TRX850 (The Japanese-Ducati One).
Previous Bikes: 1990 Honda NSR125 'Rothmans' (The smoking one), 1990 Suzuki GS500e 'Caf? fighter' (The loud one), 1987 Kawasaki GPX400r (The quick one), 1997 XJ600s Diversion (The reliable one), 2000 Kawasaki ER-5 (The spontaneously combustive one)

[Kickstart]

[quote="metalforever"]Im wanting to better understand the exhausts./quote]

So would loads of people who make exhausts!

Basics of it is the length is the important bit. Longer exhausts tend to be for lower revving engines, shorter ones for higher revving engines (basically due to the pressure waves bouncing from one end to the other, which move at a pretty fixed speed but at high revs have less time to get from one end to the other).

However it all gets far more complicated when you start joining together the exhausts from different cyinders.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Thom]

So in theory singular downpipes/exhausts which dont connect at any point would in theory be easier to contruct but could upset the pressure waves considerably, even if the pipes are the same lengths?
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Current Bike: 1996 Yamaha TRX850 (The Japanese-Ducati One).
Previous Bikes: 1990 Honda NSR125 'Rothmans' (The smoking one), 1990 Suzuki GS500e 'Caf? fighter' (The loud one), 1987 Kawasaki GPX400r (The quick one), 1997 XJ600s Diversion (The reliable one), 2000 Kawasaki ER-5 (The spontaneously combustive one)

[Kickstart]

Hi

In basic theory they would work fine. However things like balance pipes do change the way the exhaust works but I don't know enough about it to give you a useful answer on how.

Also if you make the exhaust from too large a bore pipe you loose the effect of the pressure waves.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Thom]

I plan to use similar dimension pipes but im going to increase the length so as to allow for a twin underseat conversion.

This might mean i actually narrow the pipes slightly to increase the pressure slightly, but ill let the professionals decide for me.

I'm considering trying to make one myself, and if thats the case ill end up using stainless too.
____________________
Current Bike: 1996 Yamaha TRX850 (The Japanese-Ducati One).
Previous Bikes: 1990 Honda NSR125 'Rothmans' (The smoking one), 1990 Suzuki GS500e 'Caf? fighter' (The loud one), 1987 Kawasaki GPX400r (The quick one), 1997 XJ600s Diversion (The reliable one), 2000 Kawasaki ER-5 (The spontaneously combustive one)

[Kickstart]

[Thom]

Well thats fine then because the bike isnt going to be made for performance, obviously.

Thanks!

I like the thought of just making a completely one off bike and i quite miss my gs500 as it was surprisingly fun to chuck about!
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Current Bike: 1996 Yamaha TRX850 (The Japanese-Ducati One).
Previous Bikes: 1990 Honda NSR125 'Rothmans' (The smoking one), 1990 Suzuki GS500e 'Caf? fighter' (The loud one), 1987 Kawasaki GPX400r (The quick one), 1997 XJ600s Diversion (The reliable one), 2000 Kawasaki ER-5 (The spontaneously combustive one)

[Ichy]

How much effort do you want to put into it?
I've got a couple of books, Scientific Design of Exhaust & Intake Systems by Philip Smith and one on flow dynamics that I can't find.

I've built a few exhausts but they have been for low reving bikes or plain old clunkers. A performance exhaust requires a hell of a lot of research and testing to get working optimally.
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https://www.metacafe.com/watch/1972097/how_to_behave_on_a_forum/

[stinkwheel]

Odie had some interesting ideas on how some car racing teams "tune" their exhaust systems to the engine using a piece of wax crayon.

As I recall something like they draw a line along an overlength header and look for the point where it doesn't melt. Cut it there, double the size of the pipe from that point, do the crayon thing again then fit the can.

I'm a bit sketchy on the details though, it was two years ago.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.