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LT1-LT4 Modifications 1993-97 Gen II Small Block V8

2.75" vs. 3" catback

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Old Jan 20, 2010 | 11:32 PM
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Default 2.75" vs. 3" catback
How much difference, if any, would there be on a bolt on lt1 with long tubes going into a 2.75" catback with a magnaflow muffler vs. a 3" catback with a magnaflow muffler?

I have a 2.75" catback now and I'm just trying to decide if its worth going for the 3" catback or not.
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Old Jan 20, 2010 | 11:44 PM
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what would the price difference be for you ? the stock exhaust on these cars severely limit the power from the engine. if you had the choice of a 3.5" catback thatd be even better. or true duels for the best. but a 3" catback will give you more gains then a 2.75" one. id say do it.
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Old Jan 21, 2010 | 12:16 AM
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The stock catback is 2.75". There's a reason most aftermarket cat-backs go to 3" and up.
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Old Jan 21, 2010 | 01:34 AM
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it will help a little bit but it wont be a huge night and day difference
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Old Jan 21, 2010 | 01:55 AM
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well if you plan on just having a bolt on only car, 2.75 is prolly enough, but with 3 inch you'd have more power, plus with a 3 inch you'd be good to go with many more modifications later if you want.
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Old Jan 21, 2010 | 07:50 AM
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actually a full 3 in exhaust is a little over kill on bolt on motors, my buddy is running close to 900 hp on full 3 in exhaust and its still not limiting him, id say keep the 2.75 with the bolt ons to save the money sense you already got it installed. If you do head/cam.intake swaps then consider 3 in.
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Old Jan 21, 2010 | 09:20 AM
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Don, I'm not sure where you got your info, but that sounds extreme.

I thought 3" was good for under 500hp, not sure of that number...but I'm pretty sure 900 is being choked.
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Old Jan 21, 2010 | 10:45 AM
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Originally Posted by MasterTomos
well if you plan on just having a bolt on only car, 2.75 is prolly enough, but with 3 inch you'd have more power, plus with a 3 inch you'd be good to go with many more modifications later if you want.
Originally Posted by TheDon619
actually a full 3 in exhaust is a little over kill on bolt on motors, my buddy is running close to 900 hp on full 3 in exhaust and its still not limiting him, id say keep the 2.75 with the bolt ons to save the money sense you already got it installed. If you do head/cam.intake swaps then consider 3 in.
I have no idea where some of you are getting your ideas from...

STOCK exhaust is 2.75". Most every cat-back available is 3" or larger for a reason. And why is exhaust usually the first recommended modification? Because it offers the most HP right out of the box than any other bolt-on modification by itself.

Yikes!
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Old Jan 21, 2010 | 11:27 AM
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Boy, my dual 3" setup must really be killing me. That must be why my car feels like such a terd, sheesh1
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Old Jan 21, 2010 | 12:10 PM
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Has anyone actually put a stock car on a dyno then installed a 3" catback and compared results? Mine would be a bit different as I already have the magnaflow muffler but I'm looking for more convincing proof.
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Old Jan 21, 2010 | 12:24 PM
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"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…"

taken from LT1engine.com

A bolt-on LT1 will make more than 310hp at the motor therefore a single 3" catback would be beneficial over a 2.75" system. If you ever plan to rip into the internals of the motor, the 2.75" system is going to be a big hinderance. Are you running the stock catback with a magnaflow muffler welded in? If so, simply jumping to an aftermarket 3" catback would net gains by being mandrel bent on top of being a larger diameter.
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Old Jan 21, 2010 | 01:09 PM
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Originally Posted by StealthFormula
"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…"

taken from LT1engine.com

A bolt-on LT1 will make more than 310hp at the motor therefore a single 3" catback would be beneficial over a 2.75" system. If you ever plan to rip into the internals of the motor, the 2.75" system is going to be a big hinderance. Are you running the stock catback with a magnaflow muffler welded in? If so, simply jumping to an aftermarket 3" catback would net gains by being mandrel bent on top of being a larger diameter.
yup what he said
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Old Jan 21, 2010 | 02:29 PM
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I still had the stock 2.75" exhaust on my 89 TTA when it was running 12.1. I had it dynoed the same weekend and it was 318/455 on a dynojet. Granted that was a turbo V6, it shows you can still make power with the stock exhaust.
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Old Jan 21, 2010 | 03:57 PM
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Originally Posted by Rob
I still had the stock 2.75" exhaust on my 89 TTA when it was running 12.1. I had it dynoed the same weekend and it was 318/455 on a dynojet. Granted that was a turbo V6, it shows you can still make power with the stock exhaust.
Make power? Yes. Maximum power? No.
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Old Jan 21, 2010 | 08:17 PM
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Originally Posted by Rob
I still had the stock 2.75" exhaust on my 89 TTA when it was running 12.1. I had it dynoed the same weekend and it was 318/455 on a dynojet. Granted that was a turbo V6, it shows you can still make power with the stock exhaust.
of course you can still make power, the 2.75 won't keep you from makin power completely, it'll just hold it back some.
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Old Jan 21, 2010 | 08:35 PM
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Originally Posted by MasterTomos
of course you can still make power, the 2.75 won't keep you from makin power completely, it'll just hold it back some.
Think about this statement....
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Old Jan 22, 2010 | 10:06 AM
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Originally Posted by RamAir95TA
Think about this statement....
lmfao hahahaha
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Old Jan 22, 2010 | 07:03 PM
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what's wrong with the statement? I know it's an obvious statement but that's what I was getting at...
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Old Jan 22, 2010 | 07:07 PM
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nothing, great point
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Old Jan 22, 2010 | 07:12 PM
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If catback, 3" Stainless or bust.
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