No cat

[4bimmers]

I have purchased an '87 325is with a modified exhaust system. It is straight piped all the way back to the muffler. This is going to be a track car and doesn't have to be street legal as far as emissions are concerned. Is there some other benefit to having the cat in there considering my intended use for the car?

[luvin my 325es]

The cat will slow you down, rob horsepower. Less restrictive air flow means more HP. BTW, I am considering doing same to my e30, how loud is it?

[4bimmers]

Not loud. has stock headers and Supersprint muffler.

[tonytony]

for a street car gains are minimal, but since it's a race car why not.

[SpunkyE30nOk]

thats the setup i run...well to a stock ansa muffler and its slightly louder than stock but not by much and i routinely see 35mpg on highway trips to dallas *about 3hrs south of me* it gives it a nice whoomp whoomp sound like it has a wicked cam in it.

[tonytony]

35mpg!!!!!!!!!!!!!!!!!!??????????

[JRowe]

I'm running without cats. I have a glasspack-like straight through resonator (dual in & out from Racing Dynamic - $25 steal on ebay) then y-pipe to 2.5 back to a Thrush turbo muffler. Free flowing and sounds great. Total cost was less than $100, however, the money I saved may not have been worth all the cutting and welding I had to do. Anyway, it's free flowing, sounds great, and performs much better than the stock exhaust with cats.

[s52e368]

I'm running without cats. I have a glasspack-like straight through resonator (dual in & out from Racing Dynamic - $25 steal on ebay) then y-pipe to 2.5 back to a Thrush turbo muffler. Free flowing and sounds great. Total cost was less than $100, however, the money I saved may not have been worth all the cutting and welding I had to do. Anyway, it's free flowing, sounds great, and performs much better than the stock exhaust with cats.

agreed
i did this this weekend cost around 80$-100 but for the time ehhh... however when wanting to go catless there not a single shop that will do it here.

[tonytony]

if you bring in a cat and have them weld flanges on it so you can put the test pipe on for "track purposes" they'll do it. Thats how i got away with mine

[matt]

The cat will slow you down, rob horsepower. Less restrictive air flow means more HP. BTW, I am considering doing same to my e30, how loud is it?

Not really. If you size your cat properly there is no restriction over a regular piece of pipe.

You guys with hacked up track pipes probably lose more power from that than you would with a stock cat and a catback exhaust.

[SchnellerVert]

The restriction is when it gets old and clogged, When emission system works properly It's nice to have a green car.

Ask the NASA test and tune guys about the rich Silvia turbo that was blowing fuel that our eyes stung.

[tonytony]

Not really. If you size your cat properly there is no restriction over a regular piece of pipe.

You guys with hacked up track pipes probably lose more power from that than you would with a stock cat and a catback exhaust.

good thing my test pipe came with the bavauto headers:)