Custom duals to y pipe

Custom duals to y pipe

This is an excellent summary.

Killer6 said
It's a common theory based on the premise(factual) that the gasses cool and shrink as they progress thru the system, the longer and more convoluted, the more the "heat exchanger" contracts the gasses. Go to Burns' exhaust site, They stated that any exhaust past 5' long costs power regardless of size design etc. The fact, from a performance standpoint, is that a longer system has a higher frictional factor that gets worse with higher velocities. Bigger is better. The "backpressure" myth has validity in some cases when the torque was boosted by the velocity in the system, or the A/F ratio changed in an unfavorable direction w/a big reduction.

As always with the exhaust, there's several things happening at once. However the one being discussed here, the mass flow of the exhaust gases, is the most important. Harmonoics are a consideration but Calvin Elston calls the gas flow "king".

He's been pretty generous in sharing his experiences. To the topic at hand here, this is one about merging to a single tailpipe.
Flowmaster Outlaw muffler - anti-reversion? - Page 3 - Speed Talk
followed up by Glen Urban on the next page
Flowmaster Outlaw muffler - anti-reversion? - Page 4 - Speed Talk

and dyno comparison in this one, halfway down the page.
2017: Revisiting 4:2:1 vs 4:1 headers w merge collectors in the modern era - Page 4 - Speed Talk
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