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Old 10-11-2018, 09:44 PM   #1
parb
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2.5" vs. 2" exhaust

Hi all,

i'm in the final stretch of restoring my 72 GMC Jimmy. I have gotten from a member here a set of nice ram horns for the engine.
My plan is to drop them down into a 2.5" exhaust system with borla mufflers (i have borla's on another car and i like the sound, plus i like the guy behind borla -chatted to him and he is a real nice guy).

I'm not the best mechanic so i am having a mechanic help me out. he told me earlier today that going for a 2.5" exhaust may not be the best, and that those old 350 chevy v8's needed a bit of back pressure to run right. He suggested 2" as the right size for my exhaust.

Everything i've read on this forum suggest that 2.5" is a good choice for this engine.

What do you all think? Am i making a mistake going with 2.5" inch exhaust from the ram horns all the way to the exhaust tips and i should really make that into a 2" exhaust?

I still have some time to change my mind if that is the right choice, but i would love your inputs. especially those who have put on a 2.5" system.

My engine otherwise is bone stock.

thanks!
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Old 10-11-2018, 11:06 PM   #2
truckster
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Re: 2.5" vs. 2" exhaust

"Engines need back pressure" is a myth.

https://www.youtube.com/watch?v=jjPeP_Nn2B4

Go with the 2.5. If you go with the 2 inch you'll always think, "I could have gone bigger." I've never heard anyone say, "I wish I had smaller exhaust."
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Old 10-11-2018, 11:21 PM   #3
Warrens69GMC
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Re: 2.5" vs. 2" exhaust

Go 2-1/2"
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Old 10-12-2018, 12:47 AM   #4
parb
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Re: 2.5" vs. 2" exhaust

thanks!!
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Old 10-12-2018, 06:28 AM   #5
GMCPaul
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Re: 2.5" vs. 2" exhaust

A 350ci with a 2" or 2.25" exhaust will develop more low end torque than with a 2.5" exhaust, a 2.5" exhaust helps develop more horsepower in upper ranges than a 2 or 2.25 exhaust. Most trucks benefit more from torque than horsepower in daily use.
We generally use 2 or 2.25 on stock to mild 350ci, if it's being built to race and heavily modified we then step up to the 2.5" exhaust.
Paul Jr @ GMCPauls


Last edited by GMCPaul; 10-12-2018 at 06:47 AM.
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Old Today, 02:53 PM   #6
cleszkie
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Re: 2.5" vs. 2" exhaust

If you do decide to go with a 2.5" exhaust, I suggest replacing your stock 2" ram horn exhaust manifolds with a set of 2.5" ram horn manifolds to take full advantage of the bigger diameter tubing. These are reproduced by Dorman and are a direct bolt on.
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