oh yours goes to a single
i was thinking of bringing them together then opening them out again to form an x in then follow through with twin pipes all the way back at 2 - 2 1/4 inches a pipe
I've always wanted to try independent twin pipes, although I never have.
As I understand it, the optimal configuration is what Alan Q4 and Supersprint used:
1.) equal-length primary pipes joining the correct cylinders from opposite sides of the engine
2.) equal-length secondary pipes merging these into a single exhaust
3.) the diameter and length of pipes and backpressure of mufflers is determined by application - high-revving race engine or road car that needs torque and acceptable noise levels.
This exhaust design will give the best scavenging - rather than interfering with eachother, exhaust pulses are timed so their momentum will help carry the exhaust gases out from other cylinders. Or something.
The trouble with this is that it loses the boxer sound a bit, because that sound is created by unequal-length primary pipes used in the interests of ground clearance.
If you want more of a WRX sound, design yourself worse exhaust headers, not better ones!
Subaru get away with it because they have turbocharging, which changes the rules of exhaust design.
So I believe a twin exhaust system which has a separate pipe for each bank of cylinders will be sub-optimal (poor momentum of exhaust gases, extra weight of components?) but super cool.
I don't understand this:
DONT cut the headers short (manifolds).You will loose valuable back pressure which an engine needs to function correctly.
As long as you don't make your exhaust system stop
at the headers, you'll still have back pressure - created by the mufflers, pipe bends, fake catalytic converters etc of the rest of your exhaust system.
If you muck with the lengths of the header pipes, you may be optimising your exhaust system for the wrong rev range?