Some useful exhaust info

**Ripper415** · 02-10-2007, 09:30 PM

I found this on another site and figured I'd post it here for everyone’s education...

“Hey guys I just got done reading a good article in the May 2005 issue of Popular Hot Rodding Magazine. The article was written by David Vizard who seems to be one of the most accredited and respected people in the automotive performance world. In the article he stated that CFM is a great way to help develop a zero loss exhaust system. For zero loss a exhaust must flow 2.2 CFM per horsepower (This means less than 1% of total power produced by the engine is lost due to back pressure.). From reading the article I think that a lot of people that see gains when going from a 2.5” exhaust system to a 3” dual system see them because the muffler on the 2.5” system didn’t flow enough for their application. David stated that per square inch of exhaust tubing there is 115 CFM of flow. So plugging some numbers into the good ole TI-89….. ((3.14 * radius^2)*115[*2 for a dual exhaust system])/2.2 = Max hp supported with zero loss

A 2.75” (stock) single system is good for a 310hp engine with zero loss…
A 3” Single system is good for a 370hp engine with zero loss…
A 3.5” Single system is good for a 503hp engine with zero loss…
A 4” Single system is good for a 657hp engine with zero loss…
A 2.25” dual system is good for a 457hp engine with zero loss…
A 2.5” dual system is good for a 513hp engine with zero loss…
A 3” dual system is good for a 812hp engine with zero loss…

Now these numbers are assuming that everything else is set up perfectly. The muffler must flow as much as the open pipe or more to get zero loss at the listed hp levels. He also states that using a muffler with a larger inlet/outlet diameter than your exhaust pipe is a great way to get more out of a smaller diameter system since the muffler flow will be able to match the straight pipe flow. Now there are many other things to consider when designing an exhaust system but I figured this would give a great foundation to build on.”

**Hot Black Trans-Am** · 02-10-2007, 10:03 PM

Good find!

**nhraformula** · 02-10-2007, 11:17 PM

that should be made a sticky.
its been proven here before that just changing the muffler on stock systems will gain you about the same power as switching to a 3 inch catback. the muffler is the biggest restriction in our cars when stock.

**Hurley711** · 02-11-2007, 03:51 AM

Soooo.....I am thinking about going with some duals through an X-pipe. I am running headers with an ORY, and a Volant CAI plus a TR224 cam. Should I be looking at the 2.25 duals, or should I get the 2.5 duals? In a year or so a LS6 manifold and heads will be going on, should I just get the 2.5?

**Hot Black Trans-Am** · 02-12-2007, 10:57 PM

I'd say atleast 2.5 if your going to bother with doing true duals. That was always my rule of thumb.

**BlackLT1Z28** · 02-13-2007, 07:01 AM

That's pretty sweet. Good technical stuff.

**Wesman** · 02-13-2007, 07:17 AM

Originally Posted by Hot Black Trans-Am

I'd say atleast 2.5 if your going to bother with doing true duals. That was always my rule of thumb.

Agreed. That way you always have room for more power should you decide you want to do more mods. 2.25" just seems like its too small, even with dual exhaust.

**Sam-SS** · 02-16-2007, 03:06 AM

Originally Posted by Ripper415

I found this on another site and figured I'd post it here for everyone’s education...

Any chance that the other site had the full original article?
I would like to read more on the subject. If so, could
you post the URL to it?

...>>Sam