The shockwave in the exhaust is comming back to the exhaust port of the engine. At the moment when fresh fuel is hitting the cilinder it could flush through the exhaust. When the shockwave is on time it will act as a wall so it holds fresh feul inside the cilinder. The length is set to a certain rpm range. If you are going to extend or shorten the pipe you will change the resonance of the shockwave and it will affect the performance of the engine.
Take a look on the site of Buku exhaust where they have made nice explained animations.
Originally Posted by
Alfa Romeo 159
I dont understand what could go wrong by extending the length of the exhaust, automakers have no problem making the exhaust travel all the way from the front to the back. I certainly think it would be alot safer than having the exhaust exit before the air intake with no ventalation, to where the engine is breathing its own exhaust. Can someone help me understand why the stock exhaust is like that if It isn't practical to stretch it?