Optimal Exhaust Diameter/Set Up

[Rare Iron]

Originally Posted by vector1

hows this for rule of thumb

dual 2" = 216hp

dual 2.25" = 291hp

dual 3" = 533hp

dual 3.5" = 733hp

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I would NEVER use 2" dual exhaust on ANY V-8! The pipe diameter is so small, it doesn't allow for proper expansion of the exhaust pulses & results in a lot of popping & backrapping. My rule of thumb is 2.5" up to 480 HP, beyond that you can go to dual 3" & not suffer any low or mid-range performance loss. A small block putting out under 350 HP run 2.25" or even 2.5". There is NOT a very big difference in scfm flow between 2.25" & 2.5". There is a quantium leap in scfm flow when transitioning from 2.5" to 3" exhaust. Keep in mind however, if you up the pipe diameter & run crappy-flowing mufflers, you defeat the whole purpose of the larger diameter. There are a lot of 3" in/out "performance" mufflers out there that flow like pigs! Beware!

The thing that blows my mind is most stock-type Cobra side exhaust mufflers have flowpaths under 2" in diameter. Imagine a fire-breathing big block in the 600+ HP range flowing through an exhaust passage as large as a Toyota Corolla exhaust system! How about a dual-core muffler? Looks like a regular tube muffler on the outside, but it has two staggered 1" flowpath cores on the inside. When you look inside these mufflers, there's a WALL immediately with a 1" entry into the first flow tube! Can you say 'jam a potato' in your tailpipe? Talk about turning your engine into a pump to get the exhaust out! MAJOR HP LOSS!

This was my inspiration!