What size exhaust pipe?

[swamp rat]

Got a 350 with a mild build, probably 325 hp 9 or 9.9 to 1.

Should i go with 2.25 duals and stock manifolds or step up to 2.5 duals and corvette manifolds?

EDIT: This is a K20.

[Fitz]

Originally Posted by swamp rat

Got a 350 with a mild build, probably 325 hp 9 or 9.9 to 1.

Should i go with 2.25 duals and stock manifolds or step up to 2.5 duals and corvette manifolds?

EDIT: This is a K20.

I would stay with 2.25 in diameter pipe. Here's why:

To calculate the intake flow multiply engine displacement in cubic inches by the maximum RPM and divide by two and divide that result by 1728 to get inlet flow in cubic feet per minute. yours is 548 cu ft / min. add about 30 % for the exhaust side due to heating and you get 713 Cu Ft per min. A 2.25 in pipe will flow 400 cu ft per minute so a set of duals will flow about 800 cfm. Since that's larger than 700 you are good to go, but if you want a little margin, a set of dual 2.5 inch pipes will flow 1000 CFM.

Bending and routing anything bigger than 2.5 inches is an exercise in humility; so I would not go bigger than 2.5 inches because it's just easier and I am a lazy man. I run my truck with 2.5 inches and that big block is a mite bigger than what you are running....

[swamp rat]

Originally Posted by Fitz

I would stay with 2.25 in diameter pipe. Here's why:

To calculate the intake flow multiply engine displacement in cubic inches by the maximum RPM and divide by two and divide that result by 1728 to get inlet flow in cubic feet per minute. yours is 548 cu ft / min. add about 30 % for the exhaust side due to heating and you get 713 Cu Ft per min. A 2.25 in pipe will flow 400 cu ft per minute so a set of duals will flow about 800 cfm. Since that's larger than 700 you are good to go, but if you want a little margin, a set of dual 2.5 inch pipes will flow 1000 CFM.

Bending and routing anything bigger than 2.5 inches is an exercise in humility; so I would not go bigger than 2.5 inches because it's just easier and I am a lazy man. I run my truck with 2.5 inches and that big block is a mite bigger than what you are running....

Thanks for the reply, i did forget to add i have a Edlebrock Performer intake and Worlds products cast iron (stock replacement) S/R heads, Probably won't make a difference.

But i'm wanting to go with a pretty quiet muffler such as Flowmaster 70 series or Walker SoundFX so a little restrictive, would the pipe diameter matter in this case? Thanks!

[Fitz]

Originally Posted by swamp rat

Thanks for the reply, i did forget to add i have a Edlebrock Performer intake and Worlds products cast iron (stock replacement) S/R heads, Probably won't make a difference.

But i'm wanting to go with a pretty quiet muffler such as Flowmaster 70 series or Walker SoundFX so a little restrictive, would the pipe diameter matter in this case? Thanks!

None of the performance parts matter when it comes to sizing the exhaust. It is just the volume of gas the exhaust must move. Quiet mufflers are quiet because they reduce the velocity of each cylinder pulse so they are restrictive. Increasing the size of the pipe doesn't change the restriction in the muffler, but everybody feels better with 2.5 in pipes!