VI Boost

Hey guys, I have a question before I get some exhaust work done.

I have an RMF header waiting to be installed. The collector is 2.5" and I plan to go the muffler shop to get full 2.5" piping. I want to use my stock cat and Apex'i WS2 muffler or atleast use my WS2 and get a 2.5" Magnaflow or Vibrant cat.

My questions are:

1.) Will using my WS2 muffler (2.25") with the 2.5" piping result in any substantial power loss?

and

2.) If I were to get a 2.5" Magnaflow cat, will it be emissions inspection friendly? I believe it's 49-state legal (no CA) but wanted to know if it would be like using a regular cat and won't have my o2 sensor/ecu reading anything crazy as to throw a CEL or make me fail inspection.

Thanks for your time and help.

komat

you will loose some

i have a 2.5" collector going into a worldsport catback exhaust 2.36" w/ test pipe. i lost 10hp/10tq on the dyno with my cutout closed

Sentry

1. Unless you're pushing 300hp, no, not at all.
2. Provided the car itself is capable of passing emissions, yes it should be fine. Are we talking OBD1 or OBD2 here?

VI Boost

Oh sorry forgot to mention that, the car is OBD2 (00' Civic EX) the motor is a B16a2. Yes I don't plan on going too wild on the engine other than the header, Skunk2 IM, bored tb and maybe cams down the road, but for now it's just the header and 2.5" piping. It has had no problems passing emissions before so I was wondering if changing to a 2.5" cat would change anything.

Sentry

Yeah you should be fine with that exhaust. The guy that said you'd lose some is comparing to a cutout, which of course is going to pick up some power over the exhaust having to go all the way to the back of the car through mufflers and resonators. He's also pushing considerably more power (even on his NA car) than you will be.

VI Boost

The power loss from that I can understand, but I'm asking if I will have any substantial power loss from using just the muffler alone on 2.5" piping, meaning that the 2.5" piping may have a little bottleneck to where it meets up with the ws2 muffler.

MonkeyMagic

i don't think you'll notice any difference.

2.5 to the 2.25 muffler on a dyno may net like a 2 hp loss. but the gain from the header and exhaust upgrade will far out weigh...

VI Boost

OK, thank you both for clearing that up for me, now I just need to know about the cat. I guess all I really wanna know is, will using a 2.5" cat be the same as the stock cat with the only difference being the inlet and outlet pipe size difference? I don't plan on getting a hi-flow cat so I'm just looking at the regular Magnaflow (CarSound) or Vibrant 2.5" cat.

Thanks again for your help.

MonkeyMagic

most cats really don't cause as much impedance as most think. you'll have to check with the manufacturer or retailer or reviews of the specific one you purchase.

mrharmonic

you whould lose some back pressuer

MonkeyMagic

back pressure is the devil

VI Boost

It's not really exhaust flow impedance I'm worried about, just wondering if the increase in exhaust flow from the bigger piping and bigger cat would cause me to throw a CEL or anything.

MonkeyMagic

na, as long as you have both sensors (assuming you are still obd2) wired up you should be good.