I just left from a couple muffler shops to see about replacing some cats on a 05 RCSB 5.3 and they told me that aftermarket cats don't flow better than the stock ones that basically it would be a waste of money to change them. is this true?

 

The stock cats flow better than anything GM has ever used before. I can't say for sure if they outflow say...a Magnaflow cat but it'd probably be close.

Why don't you just delete the cats?

 

My question is: What are you running that would justify the change from stockers to high flows?

 

read his location...... California isnt cat-delete friendly, as far as aftermarket hi-flow cats vs. stock cats. I dont see any reason to get rid of the stockers other than a custom y-pipe or meeting EPA regs....but thats just my opinion

 

would it be better if I got a y pipe? and what would I be looking at as far as performance?

 

again I'll ask why you need high flow cats?

I put magnaflow 2.5" high flows on my truck when it was stock with an exhaust and intake. It didn't make a damn bit of difference.

 

well I wanted some hi flo's I'm getting ready to drop a cam in it and ls6 heads and rocker arms just wanted it to breathe better

 

Oh yeah Cali...my bad. But I have to agree with you on that....unless you're going custom on your exhaust....I'd keep the stockers.

 

Have to agree, you won't see much from just high flow cats. Just get you a free-flowing exhaust. If you were going to go with some long tubes, then I'd say maybe, if you had to fab up a custom y-pipe to run them.