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Originally Posted by craig-444
Ray,
thats some good info... Seeing how dual exhaust increases the overall volume of air flow from the cat back, I wonder why exhaust manufacturers don't compensate by reducing the size of the dual pipes so they optimize air flow over the entire RPM range. Especially for 4x4 trucks most of us want low end grunt and not high HP at high RPM's. It seems they should have dual exhaust that sound/look good and have smaller diameters so the low end torque is maintained, or they should shorten the pipe length and have the exhaust exit before the rear tires. I have actually seen some custom exhaust that exit before the rear tires and it looks great when done correctly.
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Larry did an excellent job of addressing the issues that arise with dumping the exhaust in front of the rear tires...nothing needs to be added to that.
As for using smaller pipes to keep up the exhaust velocity, well, now we're getting into issues of
marketing to guys (mostly) and particularly into issues of trying to convince guys that "wimpy"
little pipes are going to provide better performance than "manly"
big pipes are going to provide. Hopefully without sounding too crude and crass here, we do need to realize that an awful lot of exhaust system purchasing is pretty tightly tied to masculine self-images where "bigger is better".
On a honkin' big 454 cu in motor, 3 inch (or even larger) dual pipes are a perfect size for low end torque. But we're working with a pretty small 285 cu in engine...and the ideal dual pipe size (well under 2 inches) just isn't, well, very "manly".
And if it isn't "manly" in appearance, it's simply not going to sell at all well...no matter what the dyno results are.
Now, for those of us who don't tightly link our masculinity to the size of our truck's exhaust pipes
, the smart approach is to simply replace the muffler (and muffler only) and
leave the rest of the piping alone at the smartly engineered 2 and 3/8 inch diameter single pipe. No it won't
look "tough" but it can sound pretty tough (if you use a muffler designed for a a "full" sound with broad appeal (e.g. Flowmaster)) or it can be pretty quiet but very free flowing for purposes like towing (e.g. by using the biggest Gibson muffler).
The bottom line is that catback duals look tough and sound tough but definitely hurt the low end grunt. Catback single pipe "systems" invariably use too-large 2.5 inch pipe and drain your wallet, add some drone, and slightly hurt torque...but they can sound pretty tough and often give you a real nice exhaust tip.
Just replacing the muffler usually keeps the torque (sometimes actually increases it...there are dyno results in The Garage showing that Spintech mufflers do improve peak torque) and will give as mean a sound as you want...but the look isn't very tough.
Your choice, your money.
