What cat-back system for my D1???

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12-01-2013, 11:32 PM

#11

timmay208

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Quote:

Originally Posted by gamble686

Right and I have seen 750hp out of a 3" does it mean that its optimal? Hell no! We are talking about when it becomes a restriction. Horsepower is all about cfm. Now one square inch of tubing will support about 115cfm. You want about 2.2cfm per engine horsepower. Doing simple math you arrive at 6.49 square inches on a 3" exhaust. That means about 747 cfm or 339hp. 3.5"=8.95"^2 or 1029cfm or 468hp. Can you build much more horsepower than that? Absolutely, but I am talking about perfect efficiency in an ideal environment.

doesnt always work like that though. ive seen back to back dynos on alot of exhaust systems going larger and not gaining anything even on lower HP setups

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12-01-2013, 11:53 PM

#12

shifty89

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Quote:

Originally Posted by gamble686

The math works I agree, but the world is not an ideal environment and these engines are not perfectly efficient. Exhaust is compressible as is any gas, and is affected by heat in the system. I'd have to say most will not see a 4" system become the restriction in the equation before other factors become the limit.
On that note 5" exhaust seems to be about the biggest I've ever seen used , plenty of vehicles pushing that well over what its' " limit" with great results.
Carry on!

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12-03-2013, 11:07 AM

#13

Vortec350ss

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Yup I think the 3.5" will be your best bet to combine flow for HP and havign the best chance of being quiet enough not to drone.

a 4" system is very hard to keep quiet on a gas engine.

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12-03-2013, 01:20 PM

#14

bobfig

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math might be true on consistent flow but you left out the "pulsing" of the engine so there are dead spots between each stroke.

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12-03-2013, 04:00 PM

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timmay208

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who makes a decently priced 3.5" exhaust? seems like all the ones i find are 2.5-3"

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12-03-2013, 04:24 PM

#16

gamble686

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Quote:

Originally Posted by bobfig

math might be true on consistent flow but you left out the "pulsing" of the engine so there are dead spots between each stroke.

Nope that cfm rating includes adjustment for pulsation.

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12-03-2013, 04:27 PM

#17

gamble686

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Quote:

Originally Posted by bobfig

math might be true on consistent flow but you left out the "pulsing" of the engine so there are dead spots between each stroke.

Nope that cfm rating includes adjustment for pulsation. Which is why that number would be different for motors with fewer or more cylinders,

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12-03-2013, 05:06 PM

#18

D1SCSS

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Well guys, Thanks for all the info. I decided to buy a Duramax MBRP 4" SS catback system. I will add a resonator if needed.... I would like a 3.5 catback but could not find one for a decent price.....