Hi EvoM..

Got my evo 8 and comes with 3" DP, exhaust and 3" Test Pipe..

Im planning to put Catalytic for smog Ca laws.. and wondering what is the best Cat for this set up? 3" hi Flow or Oem Cat?

Thanks

 

I ended up swapping out my Mil spec 100 cell for an oem cat so I can get it smogged after my rebuild. If your concerned about smog, like I am, just get an oem cat. At milder horse power levels there wont be any major loss in power anyways.

 

Will CA even pass you with an aftermarket converter? Thought the visual was strict enough to catch an aftermarket setup...

 

I got a hi flow cat and passed emissions no problem. What you should be worried about is the visual inspection, some inspectors can be aholes, luckily the one that did my car was very laid back. He asked about my Samco tube with Perrin filter but let it slide, then he asked about my flat back intercooler pipping and I just said it's a factory turbo car and showed him the small reference table on the hood that shows it. I can't remember what the values were but they were close to the average CA readings.

 

I would get a high flow cat then get an oem housing and rivet it over so you get the oem look. Worked for me in houston, no questions asked when the vehicle was inspected.

 

I say for smog put on an oem cat, then you can do whatever you wish. The oem cat is huge, so I cant imagine it being that restrictive anyhow, unless your pushing a ton of boost or are making close to 400 or more hp. If you just have bolt ons, then I say just leave the stock cat on there.

Out here cops like to pull you over for anything, another reason Im going with a quieter exhaust.

 

When I bought my car it had a test pipe and it was tuned for that - car has basic bolt-ons no extreme power levels. I put the factory cat back on - no retune - as I needed emission compliance. Power noticeably decreased and turbo surge increased. Since then I have put a 100 cell milspec cat on. Power levels came back up - again no retune - I can't really tell much of a difference to the test pipe - and turbo surge decreased. All this suggest to me that the 2.5" stock cat is a choking point if you are running a 3" turbo back, even at moderate power levels.

 

"Huge" converter doesn't always mean hi-flow...again tho, I've only heard nightmares about CA visual inspections. Adding the stock heatshields to an aftermarket pipe is a bit of effort but a great idea to prevent the need to swap parts just for an inspection every couple of years.

 

visual really depends on the guy doing it. I heard of some failing even with a hi flow cat. I'd go OEM cat for smog then switch back to test pipe or whatever afterwards

 

Look into road race engineering, they make a high flow that passes smog in cali

 

Alright guys, thanks for the help!