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jb034

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Ive got all my parts just waiting to head to alabama where the shops are 3 times as cheap as in CT. I got 2 high flow thunderbolt cats, a magnaflow di/do and 2 3.5" tips. Everything in 2.25 along with the ceramic hookers
 

flyboy1294

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Well even if you are tuned or have mods, 2.5" is overkill and I would think you want all the lowend you can have, 2.25" will cause more pop but with cats, and h pipe as close to the front as possible and the mufflers you want will be good.
how is it going to exit? going to run tips?

I don't like true duals, but I am just trying to help you out with the best performing setup.

I have heard that 2.5" was a good size to go with on 350's.

Here is a quote from dimerunner88 off of gmtruckhq, "What is a good exhaust system for my truck and will too big of a system take away low end power?
A 3” exhaust will not decrease low end power at all. A dual 2.5” exhaust system is optimum. Also, you’ll want to decrease back pressure as much as possible and many people get this confused with scavenging. A full exhaust from headers, dual or single high flow cat(s), and cat-back really provides a major power boost. The stock exhaust is horrendously restrictive. Buy a pre-fabricated exhaust kit or have an exhaust shop make your exhaust from scratch. It is not much more money believe it or not. A little reading in this exhaust section should help you make an informed decision."

Source is from the bottom of post #3 of this link: http://www.gmtruckhq.com/gas-engine...e-minded-faqs-about-88-98-obs-trucks-307.html.

This guy put a marine intake on his Vortec 350, and later supercharged it. Now he is using sometime of LSx swap I believe. Anyway, it seems to me as if he knows what he is talking about. But I could be wrong. Just my 2 cents.
 

Blue95

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I have heard that 2.5" was a good size to go with on 350's.

Here is a quote from dimerunner88 off of gmtruckhq, "What is a good exhaust system for my truck and will too big of a system take away low end power?
A 3” exhaust will not decrease low end power at all. A dual 2.5” exhaust system is optimum. Also, you’ll want to decrease back pressure as much as possible and many people get this confused with scavenging. A full exhaust from headers, dual or single high flow cat(s), and cat-back really provides a major power boost. The stock exhaust is horrendously restrictive. Buy a pre-fabricated exhaust kit or have an exhaust shop make your exhaust from scratch. It is not much more money believe it or not. A little reading in this exhaust section should help you make an informed decision."

Source is from the bottom of post #3 of this link: http://www.gmtruckhq.com/gas-engine...e-minded-faqs-about-88-98-obs-trucks-307.html.

This guy put a marine intake on his Vortec 350, and later supercharged it. Now he is using sometime of LSx swap I believe. Anyway, it seems to me as if he knows what he is talking about. But I could be wrong. Just my 2 cents.

With LT's and high flow cats, 2.5" pipe is going to not create enough scavenging on a true dual setup even with a H or X pipe. He seems to know what he is doing, but on a stock engine that makes 255 HP at the flywheel brand new doesn't need that much pipe. HE can run it if he wants to but if he wants the performance gain to be optimum then 2.25" is all that is needed, plus it costs less and is lighter, plus mufflers and cats may be cheaper too.
Now that guy with a cam and charger, he needs 2.5" for sure.

I have LT's, 2.5" y pipe into a single 3" high flow cat and muffler ran all the way to the rear bumper on my 95 with mods in my sig and even going from a 14" chambered muffler to a 18" straight through Dynomax Bullet I felt a lose in low end torque and my MPG's showed it with about a 1MPG loss on the hwy and a .25 MPG loss in town.
 
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