FOR HOURS after you have turned it off---get rid of them...OR...get some hi-flow ones.. 
Stock Cat Restriction
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From: Citrus Heights, CA
Stock Cat Restriction Does anyone know at what point the stock cats become a restriction? I have heads/cam /LS6 intake, JBA shorties, custom y-pipe with flowmaster merge and STOCK cats, and a magnaflow catback. At this point I have not decided to do LT's. Is my restriction the stock cats? Since I am not going to run LT's yet, would high flow cats show any gains? I would think the answer is yes, but would be interested to see some opinions. Has anyone been at the same point in their mods as me and swapped in some high flow cats for gains? I don't want to hear any longtube posts either, because that isn't what I am asking. Thanks.
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So nobody's been in my situation before? I guess most people would have done longtubes by now. 
Just wondering what sort of gains I'd see with some high flow cats, since that has to be the bottleneck on my car now. 
Just wondering what sort of gains I'd see with some high flow cats, since that has to be the bottleneck on my car now. the biggest gains u will see with your h/c application is going to long tubes i think. id definitely ditch the stock cats and either go ory, or if you are emissions bound, then get some nice high flow cats as already suggested.
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From: England
Originally Posted by Redneck Z
So nobody's been in my situation before? I guess most people would have done longtubes by now. Just wondering what sort of gains I'd see with some high flow cats, since that has to be the bottleneck on my car now.
Just wondering what sort of gains I'd see with some high flow cats, since that has to be the bottleneck on my car now. You have two cats, one smaller than the other. The smaller one is more restrctive, I can't remember the flow rates of them, but it's like 175-220cfm or something stupid.
Use this as a guide, 2.2cfm for every 1hp
With a h/c/i setup you should be making anywhere from 400-450bhp at the engine.
So 450 x 2.2 = 990cfm flow rate
divide by 2 as each CAT only has to deal with 4 cylinders.
You need CATS that flow approx 500cfm.
Random Technology make some that will do the job. The 8100 series is not far off and well priced, or for minimal restriction go for the 7000 series Metal Matrix ones.
Not sure what cam you have, but if its fairly mild the 8100 will be fine, they flow 450+cfm which is better than many mufflers.
BTW - if you're going to be spending the money and messing about under there, might as well chuck on some LT's too.
The CATS are certainly resticing, but it's hard to guess by how much.
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I appreciate all the responses, although I was kind of hoping for someone who's actually had heads/cam and shorties with the stock y, and then swapped in some high flow cats. I'm looking for some real world gains. I know my stock cats are a bottleneck now, and figure with my setup I might be looking at 10rwhp???
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From: England
Originally Posted by Redneck Z
So far I know of bassani and random tech. Bassani sucks and random tech is almost $600! 
There aren't too many good options that I know of. 
There aren't too many good options that I know of. the other series CATS are cheaper.
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Originally Posted by Redneck Z
I appreciate all the responses, although I was kind of hoping for someone who's actually had heads/cam and shorties with the stock y, and then swapped in some high flow cats. I'm looking for some real world gains. I know my stock cats are a bottleneck now, and figure with my setup I might be looking at 10rwhp???
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From: England
Originally Posted by Predator
The RT cats I have bolted in the stock location, but I don't believe that they sell those anymore. They have bungs welded in for the O2s, and they pretty much look like the stock cats except stainless steel. I got those 3 or 4 years ago. I can't say how much hp I gained over stock, but I probably only gained 25-30 hp with a lid, LS6 intake, JBAs, RT cats, RT y-pipe, and Loudmouth exhaust (which I've recently swapped for a Hooker). This is assuming that I was making about 300 hp stock. I always guessed about 3-5 hp for the RT cats. My dyno is in sig before the cam install.
Series?
In/outlet size?
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From: Las Vegas, NV
Originally Posted by 300bhp/ton
whch CATS did you go with?
Series?
In/outlet size?
Series?
In/outlet size?
I'll go through my receipts and see if I can find out the series number, etc.
If I were you I would buy the mufflex test pipes and keep your stock cats in your gargage for smog time once every two years. I run the test pipes and I never dynoed before and after, but there was a noticeable difference for sure. plus it sounded way better than before. The test pipes are not cheap, but they are probibly cheaper than high flow cats.