I put my car up on the hoist the other day and i have 2 questions.

1. My car has a 3inch exhaust all the way but goes into a 2inch cat, then back out to 3inch. How much power gain would i expect to see by changing my cat to a bigger one?

2. What brand and what size cat would you guys reccommend. Ive been told to buy a cat half an inch bigger than my exhaust, so that would be 3.5 inch?

 

Most people here in the USA use a 3" cat. The popular brands are from a Magnaflow and a USA based rotary shop who sells one under the name of Bonez. I believe out there in Australia you should have easy access to SMB systems:

http://www.smb.net.au/

 

You can go 3.5 front the front pipe (down pipe) all the way back with SMB (Your Lands Rotary Exhaust Gods).

 

Is this the one?



UNIVERSAL METALLIC SUBSTRATE CONVERTER

Metallic substrate converters give excellent flow rates, this universal cat has a 304 stainless steel body and heat shied, polished finish. Available to suit 2", 2;1/4", 2;1/2", 3", 3;1/2" and 4" diameter.



The design looks weird?

 

Since they have the full pipe, I would just get one:

http://www.smb.net.au/fullexhaustsystems-mazdarx7.htm

They have both a metallic substrate and ceramic cat.

 

Careful not to go with a mega flow cat or you'll be getting boost spikes like you wouldn't believe that not even a boost controller can control.

 

cheers guys ill go for the metallic substrate one.