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Camaro V8 LS3 / L99 Engine, Exhaust, and Bolt-Ons Bolt-Ons | Intakes | Exhaust

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Old 11-06-2011, 10:55 AM   #1
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Question about JBA High Flow Cats fitment with Flowmaster American Thunder Catback

I am about to buy JBA high flow cats for my car. Right now, I have the Flowmaster American Thunder Catback that is 3", and obviously the stock manifolds are 2.5". I have the stock headers because my car is Turbocharged. So, would I need the JBA cats that are 2.5" at the manifolds but 3" where it connects to the 3" catback, ORRR would I need 2.5" for the manifold (same as the other option) and still 2.5" where it connects to my catback?

I've been told by a few people that the American Thunder catback (even though 3" throughout) necks to 2.5" where it connects to the cats. So, that would believe I would just need the 2.5" to 2.5" high flow cats, and not the 2.5" to 3" cats. Then again, some people tell me something totally different.

So, is there anyone that actually knows which size I need to get . Thanks.
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Old 11-06-2011, 11:38 AM   #2
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JBA makes high flow cats that are 2.5" to 2.5" , 2.5" to 3" , and 3" to 3"
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Old 11-06-2011, 01:14 PM   #3
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Thanks Steiger, I noticed that as well.

I think the problem is that I keep getting conflicting advice as to whether I should get the 2.5" to 3", or the regular 2.5" to 2.5". Some vendors are saying that the American Thunder catback (which is 3") has a 2.5" neck down area to attach to 2.5" cats. So, that would mean I could buy the cats that are 2.5" to 2.5". Then others are saying the catback doesn't neck down to 2.5", and that means I'd have to buy the cats that are 2.5" to 3".

Damn, this is confusing haha.
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Old 11-06-2011, 02:10 PM   #4
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easiest way IMO, and this is what I did when I had my JBA 3" exhaust, is to buy the 2.5" to 2.5" cats and then IF the exhaust doesn't bottle neck down to 2.5" your exhaust shop can fab up an adapter in about 30 minutes.
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Old 11-06-2011, 02:41 PM   #5
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Get the 2.5 in, Flowmaster are 2.5 in then goes to 3.0 ...
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Old 11-06-2011, 03:04 PM   #6
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Quote:
Originally Posted by stieger View Post
easiest way IMO, and this is what I did when I had my JBA 3" exhaust, is to buy the 2.5" to 2.5" cats and then IF the exhaust doesn't bottle neck down to 2.5" your exhaust shop can fab up an adapter in about 30 minutes.
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Originally Posted by SlingShot View Post
Get the 2.5 in, Flowmaster are 2.5 in then goes to 3.0 ...
Perfect! Thanks guys'. I'll get the 2.5" inlet/outlet. I really appreciate it, and have a great rest of the weekend.
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