[oldman]

CA test pipes and secondary stock cats yield a handfull of HP IMO, the stock 2nd cats are quite big internally and are 3" in and out, with an even bigger internal volume of about 4.5" round equivalence. Plus they are near straight to the flow. Long story short, no way on a stock or bolt on engine they are going to lose much compared to straight pipe or high flow cats. This is the same exhaust as the ZL1 after all.

So, if you run CA pipes and either run the 02 behind the secondary cats or turn them off. you should have a small gain. Going to full high flow secondary cats will yield nothing measurable upto and past full bolt ons.


I'd go with JBA or other brand sub $1000 headers and $300 cats. if you are bucks down. For me I went with Kooks and straight pipe, I already had 3" cat that I welded in. I was going to just weld in the stock secondary cats but I alread the 3" from my supercharged civic and Volvo projects.. There is a brand of header out now (forget that just bolts to the secondary cats and is cheap....problem solved.