i asked about high flow cats the other day at the guy i go too and he said youd be looking at around 450 for something decent, also ive heard they dont make much difference anyway.
I got a hi-flow cat, but i cant say what it done. I bought my extractors second hand aslo and they came with a hi-flow cat attached, so it all went in a once. I have heard some reputable people tell me its hardly worth it as vr cats flow heaps anywayz.
Hi flow cats only really benefit a high performance engine. On a V6, you probably wouldn't notice any difference from a stock cat unless you had forced induction. V8's benefit more from them.
The only way your gonna really get out of the Y peice is to get a full twin exhaust. For the gain you may/maynot get out of a bigger Y peice will not out weigh the cost. Remember your car still needs back pressure to function right. You go opening the exhaust up to much you will lose alot of power....you may gain it back at 8000rpm but thats no good going to the corner store.
Thats not quite correct. Back pressure in any form is bad. What you are chasing is exhaust gas velocity. A system that is too big can create more back pressure than a system that is too small.
The stock Y piece on a VS V6 is 2" anyway and is not restrictive at all. I would leave it. And it is stainless.