New cat vs. straight pipe
 

I'm considering ordering the SS Auto Chrome exhaust system, and I was wondering if the catalytic converter that comes with it adds much backpressure? Ideally I'd like to go with a section of straight pipe where the cat should be, but I don't want my car to stink and word on the street is that central Indiana is enstating emissions testing sometime in the next few years. How much of a performance difference is there between the SS Auto Chrome cat and a straight section? Also, I want to keep this car as low profile as possible (plus I just don't like ridiculously loud exhausts), how much more backpressure would a presilencer add? Does a presilencer replace the downpipe? Sorry I know this is a lot of questions, but I just want to get as much information as I can before I go and drop $500+ on an exhaust system.

1. Most cats add a significant amount of backpressure.
2. There will be a very noticeable difference between having a cat and a straight pipe. Racing beat claims that taking away the cat restriction can easily net 13% hp increase. Also, your car will rev faster with the decreased restriction.
3-4. Removing the cat will increase exhaust tone slightly, but not nearly as significantly as mufflers. You may want to consider a presilencer as the straight pipe to replace the cat -- or anywhere in that line. The restriction would be less than a cat as typically these are insulated straight pipes.

Other concerns: It will be a good idea to have the cat switchable. Keep in mind that running without a cat will make people not want to stand/drive behind your car and slowly kills small children. A great idea would be to put the straight pipe on for track and autocross use and use the cat for the streets. I know, exhaust systems aren't cheap - I'm going to work on welding up my own.

str8 pipe all the way, WOOO!!

Yeah, lose the cat. The gains a very noticeable. I have a RB pre-silencer there instead, so the exhaust has a really nice tone, even with the GP Sport exhaust.

Without a cat your car will stink like hell. I couldn't even drive with the window down (made me nauseous) it really stinks. If you drive this car as a daily driver I would highly suggest what sar said.

Go with a straight pipe section for the track and cat for the street. You can switch them out in ten minutes or so.

whats up with indiana trying to do this emissions stuff. i know that 4 counties do it, but i havent heard anything about central indy...... that would make me very sad.

Brian

Would a High-Flow cat cut back on the smells of the exhaust as much as stock?

i have an FB with a straight pipe but yes it does stink and people( friends) will tell u it stinks but it is a good hp gain try putting a presilencer on there. dont worry about the cat rotarys stink anyways

I swapped out my 3" RB presilencer for a 2.5" highflow cat temporarily to pass emmisions and I swear to god the cat made my car smell like ass. Performance was impacted as well, obviously. But when I swapped the presilencer back in and drove the car around the block the power difference was very noticable and the bad smell went away.

Someone created a thread a while back claiming that the new cat they installed made their car smell worse. I thought they were just crazy until it happened to me!!