Ok so here's the plan: i would like to get rid of my stock exhaust piping, get a new muffler ( i got some nasty 3A racing one right now), and get a high-flow cat.

1) i want 2.25 piping so should i buy the 2.25 high flow cat? it may seem obvious but i really don't know.
2) we don't have emission laws here, should i get a test pipe instead? (whats the difference)
3) does the inlet of the new muffler need to be 2.25? alot of the ones i'm looking at are 2.5 and i didn't know if they welded some kind of adapter or something on there.

i guess thats it, i'm a newb when it comes to exhaust...

thanks in advance!

1. + 3.) you should be fine getting everything 2.25. When I had mine installed I had a 2.25" cat back installed and my exhaust was a 2.25 as well. I watched the guy put it on and he kept going back and forth between his pipe bender and my car. He just kept making the pipe a little bigger on the end so that it would fit over the exhaust. So I know if you get the same size an exhaust shop should be able to do it. If you get it bigger I would assume that they could make it smaller but i'm not sure on this one...

2.) WHERE DO YOU LIVE!!! I wish i didn't have emissions laws, i'm in california and it sux...Anyway is your question regarding weather or not to put a high flow cat on or the resonator? If you take the resonator off your car will be louder. I know cuz this happend to me. The stock one is too small to fit on the 2.25" and I didn't have the funds at the time to buy one so i just left it off. The car is SUPER loud but it tends to be whiney. I like the loud but the whiney noise kinda sux. IMO I would say just take off the cat, if you don't need to pass emission. There will be alot of people to tell you differnt tho...

cool deal. i live in kentucky

its not that i want ''loud'' cause my car is plenty loud with the headers/muffler combo i have right now, i just want a different sound. and unfortunately the muffler i want is sure to sound ricey as well. it just looks cool, thats why i want it.

so it would be ok to get a muffler with an inlet of 2.5 but have 2.25 piping?

It should be fine, as he said before the shop could mod it out for it to fit on your cat back. If you don't really require a cat, I say don't get one. Go for that test pipe you were thinking about. Although then you would be a polluter as many would say on here...Shame on you? Oh well.

oh well indeed

i think i read somewhere though that you only get 2-3 more horses on a dyno if you get rid of the cat. and i'd rather be a little more eco-friendly if it just means 2-3 horses. i wouldn't really feel that.

>

I would if I could. Here in Cali exhuast shops refuse to take off your cat without replacing it with another one. I guess there is a big fine if they get caught. I plan to get the high flow cat for my car but I would go without one if I could.

The cat helps make your exhaust note quieter. I highly recomend you keep a cat on your car unless you have some serious mods to support a test pipe. The world is polluted enough as it is.... If you get a high performance cat, makes sure its the same diameter as your piping, or you might as well stick with your original one. There are isn't much of a performance increase switching to an aftermarket unit.

I recomend you try your best to keep your exhaust diameters as close to the same size as possible. The weakest link in an exhaust is the smallest diameter. So if your getting a 2.25 cat, there is absolutely no reason to use 2.5" piping (unless your getting crushbent).

If you have a 2.25" inlet on the muffler and a 4" exhaust outlet, it will actually project the sound louder. Kinda like the flared opening of a trumpet.

thanks alot, this all makes sense now. that sucks about the exhaust projection, mine's loud enough as it is... lol

Just thought I would add my $.02

I have had a straight test pipe with no cat and with the engine running properly had no issues with emissions. However, I do live in WA so our emissions may be a bit less stringent as other states. I did compare the emission reports from the old exhaust (stock with cat) to the new one (w/o cat) and there was a insignificat difference, with some emissions being the same.

(though I must add this is a 5th gen '91 Fed emissioned 5sfe)

-Terracar