I currently have a 2004 6mt with an aem intake and helix straight pipes. i plan on buying an hks exhaust and ultra ss pulleys. I was wondering if i should put my cats back on when i install the dual exhaust because of the loss of backpressure. I always thought that the less backpressure the better, but i remember from highschool auto that some backpressure is necessary to gain horsepower, but im not sure if that was for f/i or n/a engines. If someone could please tell me what the best set up for me would be, it would be greatly appreciated. thanx, race on.

 

so..... i see everyone is so interested in my post, or maybe no-one knows the answer, but i asked my buddy, a tech at a bmw dealership, and he said to put the cats back on so that i could get back the low-end torque i lost when i took them off. he said that with the cats off i gain high-end horsepower, but the gain in low-end torque would be better. so if anyone has an opinion feel free to reply.

 

Backpressure in itself is not good or bad. You are correct, our cars require a certain amount of backpressure to operate it their peak. Too much backpressure and your car will become a golf cart.

My recommendation for you would be to get high-flow cats. I'm not a big fan of test pipes as you will lose your power on the low end (without a doubt)........if you are NOT using a turbo or supercharger.

I'm running Crawfords right now and love them. There are other brands out there.......just don't get the Random Technologies (the one's they make for the G35 are rediculous).