Quote Originally Posted by Chris_F View Post
But that's the problem. You can't just add up the individual flow of each muffler and say one flows better than the other. It's more complex than that. How about the increased turbulance created by the y-join? The reduction in velocity of exhaust gases caused by splitting the exhaust gasses and forcing them to twist and bend through the extra piping and the extra muffler?

Also, faster traveling exhaust gases will create a scavenging effect that pulls subsequent exhaust pulses through the exhaust.

My main point though: if there was a true performance benift to a dual outlet exhaust on a 4 cylinder car (not talking about noise reduction or looks) why don't all of the tuners who are obsessed with extracting every last HP out of the k-series go with a dual outlet design?

By the way, I'm not saying that a dual outlet exhaust can't flow just aswell as a single (depending on the design). I'm saying that a single outlet exhaust is all that's needed regardless of the power figure you are chasing. It's also more straight forward to design a single outlet exhaust that will give you the flow you need for your setup.
Ultimately up until the split a single and dual outlet catback run the exact same course and you're right when you say the main problem is in the split but you'd assume a good aftermarket exhaust would have a good-quality split that won't disrupt flow that much. But a single outlet exhaust still has to bend in the same place at roughly the same angle as one of the dual's. What's the say it's impossible for the gas to flow as well if it splits before the corner as if it just stayed all together around it?

Not saying you're right or wrong but just looking at it from another perspective