Could someone please tell me what the difference is between a stock cat, hi-flow cat, and a test pipe is on a turbo back exhaust. How much restriction is there, and is there a noticeable hp gain. Thanks in advance

 

A hi-flow cat is just that, a higher flowing catalytic converter. It's built much the same way as a stocker but with less-dense material and chambers.

A test-pipe is just a section of exhaust nothing inside.

You will get the most hp gains from the test pipe since it has no restrictions to the exhaust flow. The high flow cat will offer a gain over stock but not near as much as the test pipe.

 

Are either of the test-pipe or high-flow cat legal? Which is more noticable as far as rotten egg smell and more smoke? Or is it the same? Whats the HP difference between Stock, Hi-FLO and test pipe.

 

high flow cats are legal. running without any cat is highly illegal.

 

From High Flow cat to Test pipe with no other changes yielded 15 more HP! Dyno verified

 

are you sure about that? I doubt the test pipe will yield 15 more hp over the High flow... do you have any dyno pictures? anyways... I heard that Hi-flow's after a while might shrink the margin of passing smog...

 

Thanks for the reply everyone I think I'll be going with the hi-flow cat. I don't want to swap anything out for emission testing or have to deal with fed. fines.

 

My hi-flow cat is half the size of the stock one and I personally do not think it will pass emissions but I atleast it will keep me from fines, louder exhaust note...

 

I'll be getting a high-flow cat soon for the extra performance and also to save my stock cat from the abuse. I plan on keeping my stock cat for smog tests. High flow cats seem to fail after about 3-5 years of use.

 

If you live in CA, don't even think about test pipe! Just like twinevo said it is HIGHLY ILLEGAL in CA.... but then everything is illegal in people's republic of california so i guess it's all up to you

 

I have the Helix HF Cat. I like the added HP but don't like the extra exhaust noise and exhaust smell. A test pipe will be even worse.

Test pipe will give the most HP but you'll need a CEL fix and the exhaust will be pretty loud and it will stink much more. Also, I've heard with test pipe, you'll shoot flames out the tail pipe.