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Old 11-02-2006, 04:50 AM
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Is There An Exhaust Size Rule Of thumb To HP Rating?

Hello

I spent a few hours now reading old thread on exhaust size and can't really nail my question down. So here it is.

Is there Rule of thumb to exhaust size and horsepower? Or, What HP should one jump to 3" Exhaust?

I Have a 64 Nova 355ci with 450 HP. It has an narrowed 456 posi with an 400 turbo trans. 3800 rpm stall. I think the headers are 1.75"

I am going in the morning to get an exhaust system all the way out the back and just wanted to know what size I should get. I already have the some magnaflows on the car that dump at the door. This is a drag car that I am converting mostly for the street but will take to the drags here and there.

Thank in advance.


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Old 11-02-2006, 08:48 AM
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As far as tubing size is concerned, the first 6 feet is the most important, the header primaries, collector, headpipes and crossover. After the crossover pipe the size becomes less important. We run a full 2-1/2" system on our 490 hp 64 Nova road racer, I ran the same setup in my 11.7 second daily driver 67 Nova.

One of the biggest mistakes made is reducing the collector size before the crossover pipe.

Jim Hand did some testing with his 455" Pontiac:

http://www.pontiacstreetperformance....p/exhaust.html

If you don't have a crossover, the total length of the system will have a greater affect the wave tuning than with one.
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Old 11-02-2006, 02:12 PM
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I think 2.5" ID should be good to 500hp. Just make sure when you go to the muffler shop they know if your talking ID or OD. Yes some are really that stupid.

I took my truck in for an exhaust one time and they asked if I wanted 3". I said no 2.5 and it turns out their idea of 2.5" is OD so just make sure your on the same page.
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Old 11-02-2006, 04:31 PM
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Ehxaust

Chevy High Performance did a story on this a while back. I believe 2.5 inch to 500hp and 3 inch was good to 800hp
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Old 11-03-2006, 12:12 AM
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Good advice. Incidentally, I saw an episode of Trucks on Spike TV and the guy was peddling 5" exhaust for stump pullers!!!! Some guys really need to compensate I guess!
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Old 11-03-2006, 12:35 AM
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Thank you all that replied.

I also wanted to say that I think this site is great. I have found only a few days ago and already been reading until I can't see strait. So much info here and I only just started.

I will go with the 2.5"

Again thanks to all that replied and to the creator and the folks that keep this site running.

Back to reading.
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Old 11-03-2006, 06:31 PM
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exhaust

they did a pretty good thread on 460.com about exhaust size and how the different mufflers performed you might want to check it out.
Nice ride!
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Old 11-04-2006, 10:52 AM
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Quote:
Originally Posted by droddy
they did a pretty good thread on 460.com about exhaust size and how the different mufflers performed you might want to check it out.
Nice ride!
What's 460.com? If I wanted to check it out, how would I find them? Going here http://www.460.com/ gets me nowhere.
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Old 11-06-2006, 08:34 PM
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www.460ford.com

it's www.460ford.com

Sorry about that
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Old 11-07-2006, 12:38 AM
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Vizard's rules of thumb: A pipe will flow 115cfm per square inch of cross-sectional area. You need 2.2cfm of flow capacity per horsepower.

http://www.pontiacstreetperformance....p/exhaust.html is a good article on mufflers, etc.
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Old 11-07-2006, 12:59 AM
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Quote:
Originally Posted by jimfulco
Vizard's rules of thumb: A pipe will flow 115cfm per square inch of cross-sectional area. You need 2.2cfm of flow capacity per horsepower.

http://www.pontiacstreetperformance....p/exhaust.html is a good article on mufflers, etc.
Thanks for that link. Very good read.

George
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