I don’t know about how they work in a street application, but on our race engine we found that with the “X” pipe we had a gain in torque and HP. But after over 50 dyno pulls with our mule engine and countless header designs, the best scenario we found was a three into one system with a “Y” pipe and properly designed anti-reversion cone for our engine.
If you look at the effects of wave travel in an exhaust system, pressure waves, both positive and negative, are traveling up and down the pipe, and depending on the type of wave and when it hits the engine, it can help you or hurt you. A negative wave hitting the chamber during overlap is a good thing, it helps the next intake charge and results in more cylinder fill. A positive wave does the opposite and can cause poor fill, excessive heat, and even detonation. The idea of the anti-reversion cone is to let the negative waves pull exhaust out of the engine more easily than the positive waves push exhaust back into the engine.
Also we played around with the length of the collector till we found the optimal length, which had a lot to do with the HP and torque gains. We did all our design and testing with one of the best NASCAR exhaust guys in the country Boyd Butler.
