When to go bigger?????

[swifter]

Can someone tell me when you move from 2.5 to a 3.0 exhaust????? Is there a certain hp rating??????? A cubic inch rating???? Thanks Guys-Steve

 

[airwoofer]

I used 3" on my 416. Fit OK and works well judging from the time slips.

 

[emnestor]

I believe high compression motors work best with the 3.0 inch exhaust.

 

[notenoughcash]

Basic flow calc for exhaust, feel free to double check my numbers for cfm/sq inch, this is off the top of my head while killing time in a worthless meeting at work and it's been awhile since I've needed to do this

~ 2.2 cfm per HP needed

HP*2.2 = total CFM

Divide by two if running dual exhaust

Assume 115 cfm /sq inch of exhaust so...

3.14*r^2 for pipe sq inch * 115 to get potential flow per pipe and see if it meets your needs

example:
650HP --> 325HP per side
325*2.2 = 715 CFM per side

3" exhaust = (3.14*1.5^2)*115 = 812CFM per side <--good to go with headroom

 

[srduster340]

From what I understand, unless you're making 600hp or more stick with 2.5". 3' is the "thing" now and sounds good when you tell someone you got it but not necessarily needed. Of course I'm no expert.

 

[bOb shingler]

use the same size exhaust pipes as you collector.

 

[airwoofer]

Right and for my TTIs that was 3". I gained over a 10th over an open collector with the 8" extension when I put on 3" X-pipe and flowmaster 40s with a 3" x 8" cherrybomb in front of them.

 

[Lonewolf3165]

Use the 2.5" pipes & keep building more HP until they blow apart like a Bugs Bunny loaded cigar & then go to the 3". Lol.

 

[72BBSwinger]

My old 3" H-pipe setup no longer fits after the 6 spd. goes in so I figured wth and am going with a 3.5" Pypes X-pipe kit and some 16" x 3.5" Borlas I scored off of Moparts. Probably will put some 2.5" turndowns on it to tame it down a bit. Plan on a bigger engine in the future so figured might as well design this exhaust for that instead wishing I did later.