Quick question...How big should the gasket be that goes between the downpipe and the main cat?
Thanks,
Matt

 

Is your DP 2.5"or 3"? But I think a 3" gasket is what you need.

 

I have a 3" Pettit dp. It came with a gasket (3"), but I did a shitty install job and the gasket is useless now.
I thought, though, that most people just go to Mazda to get a replacement gasket.
This is what I did, but the gasket they gave me it is not 3". Maybe 2 or 2.5.

 

I believe the stock gasket size is 2.5 inches, because that is the size of the stock cat opening. Most everyone just uses the 2.5 inch gasket.