Which cats 2.5 or 3?

[mit]

I got my browned side sills repainted under warranty. I need to get a high
flow cat and while I am in there I am going to get a Corsa cat back exhaust
(if anyone has one for sale cheap send me a PM). For now I am going to use
stock headers. Should I get the 2.5 or 3 inch high flow cats? And should I spend
the extra money for the honeycomb substrate?

 

[SoCal Rebell]

I got the Randomtech 3" in/3" out to go with my 3" catbacks.

 

[mit]

How do I connect the 2.5 inch stock headers to the 3 inch cats? Muffler shop or is there a 2.5 to 3 inch connector?

 

[SNKEBIT]

should be able to get a connector at any good parts store.

 

[FE 065]

Doesn't Corsa make both 2.5" and 3" catbacks? If you're using their 2.5" system I'd say stay with 2.5" cat if it's that size all the way through.

A larger core would disturb the flow through the cat and probably further down the 2.5" pipe afterwards as the outer portion of the gases are diverted to the larger diameter due to the , then are shoved back into a 2.5 inch pipe.

You'd probably so more harm than good widening the pipe to 3" for a very short distance, then narrowing it back down.

If you're using a 3" Corsa catback, I'd still kind of ask, "Why slow down the exhaust gas velocity any nearer the engine than necessary with a 3" cat when you could keep the 2.5" cat ID for another foot or whatever.

You might even want to cut and fit a megaphone for the transition from 2.5" to 3" to fit in between the back of the cat and the front of the catback. Though most available megaphones have too large an included angle to travel the approx 2' from the cat to the catback without exceeding 3" diameter by the time you get to the catback, the megaphone would cover most of the distance..

 

[ViperJoe]

Corsa no longer makes the 2-1/2 system. If you are doing tubes and filters even headers the standard hi-flow RTs will be fine. JonB @ PartsRack is an RT distributer and sells the 3" to 2-1/2 stock header pipe reducer that goes on the forward end of the cat.
I am very pleased with my hi-flows and Corsa cat back system.
Good luck!

 

[motor602]

what kind of power gains can be expected by going from the stock cats to RT's on a late (2000-) gen II?

 

[sbkim]

Quick question - I am getting ready to purchase 3" borla system and 3" RT cats. Will the borla fit directly on to the 3" cats or do I need reducers to fit. The reason I ask is that Borla claims that their system is designed to fit stock cats (ie. 2.25"). Thanks

 

[Casey]

You are going to have to Cut & Weld a 3" piece on. Not difficult. But from my understanding the Borla muffer still has 2.5 inch inside, so that would be taking away from the flow even with the 3' HF cats! I will be taking my borla muffers off this summer and checking them out inside to find out for sure. I have 3" mufflers ready to go on.

 

[sbkim]

So I should just get the 2.5" cats then right?