Quote:
Originally Posted by Carlito12
great info ! thx ! 
it appears 3" separate pipes is the best way to go for performance... |
In the case of the BMW, 3" is overkill since there are two exhaust systems. In other words, if we are talking about a 400hp car, each exhaust system only needs to support 200hp. Keeping things separate is, however, a good idea. The idea of using an X-pipe for post-turbo scavenging effects is flawed. There are no discrete exhaust pulses in the exhaust system since the turbine wheel "chops" up the exhaust flow. If there are no discrete exhaust pulses (separated by vacuum pulses), exhaust gas scavenging never comes into play. All an X-pipe will do is increase backpressure which will reduce power.
Shiv