The first section is usually quite short and there is a point where it works best and making it longer/shorter can tune the revs and I believe as little as 1mm can alter where peak power is by around 100rpm. Maybe needed to alter this if the bike is tuned? High tune bikes (nsr/rgv etc) need it to taper right from the engine.
Most important part of pipe is the rear taper to "bounce" pressure back but front taper also has to be right to allow pressure wave to travel back properly. Not to sharp not to shallow.
The volume of the chamber effects torque, larger = torque lower down.
I think the length of the pipe after the chamber is not so important. Sure it does something, can't remember.
For these reasons the RGV pipes which go 2 up one side are NOT ideal. They sacrifice a little performance for cosmetics (oh well, I am a fashion victim then becasue I like them!). The best styles for performance are one each side where by the tuned lengths are identicle.
The steeper the rear taper I think means a narrower power-band but higher power? To a point...........like everything else it's all a compromise on a mass produced bike.
In the RGV world there are lots of pipes to choose and pipes from different manufactures give different characteristics, ie Arrow "seems" to suit a road stock bike giving good mid-range and peak but dies quickly after peak. A Lomas pipe seems to give less of a mid boost and peak by a hp or 2 but allows the engine to rev on much further which would seem to suit for further tuning work. Given this I think you need to choose pipe carefully.
If you are a racer the dream situation would be to have a pipe made to tune the enigne to give power exactly where and when you wanted it to suit your particular tune. A pipe like this would be then useless on say a stock bike. Because one pipe is good on one bike doesn't mean it will work on another if the tune is different.
Forinstance if you get a 300 conversion done on an RGV there is no pipe specifically made for the 300cc engine and it's characteristics. I am sure the 250 designed pipe must be a restriction to getting the best out of it. It's where I was going to look next before I sold the 300.
Of course having considered all this it needs to FIT the bike and look pretty good without restricting the rider in terms of ground clearance or burning his legs
Want to be an exhaust designer? Sounds like a real headache!
Anyway, just as I understand it, I am not saying I am 100% correct so if any experts are reading please educate! Exhausts = Magic
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http://www.thetuningworks.com