EXHAUST SIZE? Anybody have a formula?

[pwdart]

Because of packaging problems with a truck Im building Id like to run a large single exhaust but how big is big enough? Its a 408cid turning 5000rpm. My formula tells me I need a 600cfm carb but what formula is there for exhaust tubing size? Id like to use a diesel exhaust pipe which i can get in 3 or 31/2. Id like to use 3in if its enough because mufflers are easier to get. I would think 3 in would be enough I mean a mack truck only has a 4in pipe and its 672ci and turbocharged!

[djswwg]

Ya but the Mack engine only turns about 2200 rpm max, and as you said it's got a blower to help shove everything thru. I'd go at least 4" if possible, even 350 Vette's need that much (single) pipe to make semi-serious horsepower, and your engine is in the big block size range. Unlike cams and carbs, bigger is better when dealing with exhaust. Now I know there's at least one guy out there who's gonna remind us about overscavinging and upset carb singnals blah blah blah, but for wide open throttle performance go BIG!! cheers..........djs

[pwdart]

i also should have mentioned that all out horsepower is not my goal im looking for low to midrange torgue like to pull a trailer with

[djswwg]

that's OK, I'd still go 4" if room permits, it would be about the same as 21/4' duals. let us know your decision and the results.......djs

[rumblefish360]

The formula as per "Flow Master"

"Single pipe" in the 350-450 cid area.

3.00 300hp
3.50 350hp
4.00 400hp

These were guide lines for wide open throttle, the next size smaller diameter pipe is suggested for daily street driving, again, as per Flowmaster.

[Hammer 74]

Remember back in geometry class when we learned that the area of a circle was equvalent to PI x r squared. If you use that formula this is what you get.
Duals
2" = 6.283
2.25" = 7.952
2.5" = 9.817
3" = 14.137

Single
3" = 7.068
3.5" = 9.621
4" = 12.566

a single 3 inch pipe has a larger area than 2 2 inch pipes. Seems a little screwy but numbers do not lie. A 4 inch single pipe is the same as 4 2 inch pipes or 2 2 7/8 inch pipes. Maybe this will confuse you some more. Hope not.

[Fury Boy]

Wouldn't it be a lot easier to do duals? I would think that it would not cost that much more. Just add a crossover to 2 1/4 in pipe. I think that summit makes a clamp together kit for like $175.

[pwdart]

thanks for the replies. cost isn't an issue as much as parts availability. I was hoping to use a diesel tailpipe as this is a daily driver and when parts go bad I would like to be able to get them at NAPA etc. It seems the diesel pipe will be to small unless I get one from gale banks or a similar source. The universal kits from summit are universal...they don't fit anything! I haven't seen a dual kit for a 72-93 that I've been pleased with its just a funky chassis lay out. I found a formula for exhaust cfm (exhaust temp +460)divide by 540 x intake cfm. Now just need to find out how hot the exhaust is and how much certain pipes will flow with no more than4" hg restriction. I found this in a commercial exhaust system parts book.

[9dodge]

if your looking for low and midrange torque, then bigger is not better. Go with a little smaller exhaust to get the torque in the range you need.

[CaliRogue]

you'd be best off going to a reputable muffler shop in your area and have them fabricate a 3.5" single pipe (or 3" duals) system for you with a good set of hedders, 4" will be major overkill on a street driven rig, not only will pipes that big kill your low-mid range power, they'll also cost you big-time when it comes to fuel consumption (OVER scavaging the cylinders during the exhaust cycle) 3" - 3.5" pipes have been used on anything from a 195hp 318, all the way up to 500+ hp 440s ... as far as parts availability? ANY muffler shop worth it's salt will carry, or be able to readily obtain 3 - 3.5" components, where alot might not carry those big-ass diesel parts.

just my 0.02 worth.
later
CaliRogue