Aliate X

posted by accident

FoxGT

For best performance exhaust are supposed to flow around 250ft/sec. This book makes it seem weird. To me what im at should be like dual 1.5. I think i'm gonna have to say f*** this book I'm sticking with my 2.5.

http://www.magnaflow.com/07techtips/faq/question10.htm

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FoxGT

Pipe Sizing:

We've seen quiet a few "experienced" racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.

As discussed earlier, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car.

vfast

your seem confuse some...header wraps, coatings keep heat in the pipe to speed the gases up, yes going to a too large pipes hurts hp anything bigger than 2.5 duals it a waste of $$ and will hurt performance...going to the 3" tail pipes will not hurt hp nor help as the gases have cooled some. header length has alot to do with hp increases and rpm ranges as they need to be tuned to the engine when high hp's are present

FoxGT

I just said the wrap helps keep the heat inside the exhaust. What I am saying is the 2.5" will be able to keep that heat for longer than the 3". It gets out of the exhaust faster because of the size of the pipe being smaller, but go too small in size & you will end up choking keeping some of the exhaust in the cylinders. You can't really base this off of hp, but most of the people in this forum don't know how fast their exhaust flows. This is why people made hp/exhaust size charts. & According to these charts people in the 250 - 500hp zone 2.5" is the best.