Dual vs Single Exhaust

[BB6Mustang]

Is there any real benifit from dual vs single exhaust assuming the same cross-sectional area (ie. single 3.5" vs dual 2.5")? Theoretically the the single should flow better due to less surface friction and have a slightly higher exhaust velocity (maybe insignificantly better). Also would the two smaller pipes be quieter than the single (I've heard that larger pipes are louder)? Would there be a difference in sound? Anything else I haven't thought of?

 

[Anonymous]

A big single should have a lower tone, which I prefer.
I think most duels were installed because they could not fit a big single and the even bigger muffler under the car. That said you can easly fit a 2.5 single system under a fox body and somebody does/did make a 3".
Frankly I like the simpilsity of having just one system to maintain instead of two, should be less expensive as well.

 

[BB6Mustang]

Thanks kev@ia, anybody else have any words of wisdom?

 

[Anonymous]

I have tried both and some of the best results I have had were with the single exhaust properly sized. I think it works like a "X" pipe. It also seems to work best in smaller engines mostly due to packaging constraints. Say my 250 6 turning somewere over 7000 RPM a single outlet woud work fine. My 351C turning 9000 RPM and kicking out 740 HP would be tough to package even rougher in the fact its in a rear engine configuration. One of my best 6 cyl exhausts was Hooker headers dual outlet "Y"ed into a stock right side exhaust from a factory 302 Boss.

 

[MustangSix]

If you look at a really great inline six exhaust system like the one on a BMW M3, you'll see that they have duals which meet in a x-pipe, then duals to a resonator, then duals to a muffler with dual outlets. It is very highly tuned, so much so that I've seen tests of aftermarket mufflers that made more noise, but caused horsepower loss on that engine. It's very hard to improve on and is highly optimized to be part of the engine.

But it's that highly refined tuning that makes the difference. Just slapping on an x-pipe or a crossover may not gain you anything unless you know exactly where to put it and what size to make it. And then it has to feed a resonator that is exactly the right size, length, and locaation to feed a muffler that's exactly.....well, you get the idea. But that's part of what it takes to coax 330 naturally aspirated hp out of only 3.3 liters.

The point is, it takes either a lot of trial and error or a lot of science to determine the "best" system. In the end, the difference between a pretty good single exhaust and a pretty good dual exhaust can't be felt in the seat of the pants.

But, IMO, pure duals w/o a crossover sound better, and that's what really counts on the street!