OldSchoolSS

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.

Just a side note that he stated that I thought was neat... “Just as fish don’t feel the weight of water, we don’t readily appreciate the weight of air. Just to set the record straight, a cube of air 100 feet square will weigh 38 tons!”

Hopefully I’ll get some more understanding of flow in a closed space in my fluid dynamics class next semester.

jrp

iTrader: (16)

check the exhaust guide

OldSchoolSS

Wow you put the whole article in there. I was going to say I didn't see that in there before but I guess it was just posted two days ago. Well you can throw my calculations in there if you want it might save some people a little bit of time.

jrp

iTrader: (16)

sure i'll add it in there

and yes i just put it up a few days ago.

DAPSUPRSLO

iTrader: (14)

Another thing to consider is that you must obtain a correct collector length to take advantage of pressure wave scavenging for your desired rpm. From reading his article it appears that you must either use a baffled style muffler to not have an effect on collector length or use some of his pressure wave boxes and the appropriate mufflers. I wish flow master would publish flow numbers of their mufflers as they are a baffled style muffler which would not effect collector length. Anybody know of any other muffler which are a baffled style? Maybe the spintech mufflers.

technical

Flowmaster mufflers aren't truly baffled. The would be baffles open up on the sides to create chambers. Turbo mufflers are a good example of a baffled muffler.

DAPSUPRSLO

iTrader: (14)

Good information. Vizard's articles are very non-specific on which type of mufflers he considers baffled and what not. If you don't mind would you take a look at another post I put up. https://ls1tech.com/forums/generation-iii-external-engine/336065-high-flowing-baffled-muffler.html
Looking for a 900-1000cfm baffled muffler. I take it the welded dynomax mufflers would not work as they are still straight through but with a large chamber. Thanks.

technical

I mostly stay away from the baffled mufflers because they tend not to last very long. You would definitely need to find a stainless steel (inside and out) baffled muffler if you don't want it to rust and internally blow apart which they are notorius for doing + adding a **** load of backpressure.