http://www.protegeclub.com/forum/sho...threadid=10212

Well since my other post was closed, I will start a new thread.

Ok, I have the stock 2.25 size pipes coming from my catback. I took the resinatior out for sound. Then I have a reactive bomb muffler. So I guess its mostly straight through. What can I do to add just a little more back pressure?

Please give advise with out closing the post

 

First off, the stocker is approx 2.1" not 2.25" (it's metric). Next, the stock diameter necks down to 1.9" OD right before the axle. This is the part you should replace along with using a better muffler. Really, you don't need MORE backpressure. If you used a complete 2.25" pipe from your cat all the way to the rear, you should be running fine. I'm using 2.5" and didn't see any real losses in low end torque. I wanted to go larger because I'm going to go supercharged this fall.

 

Now I understand how it all works. I like how it has explained. Thankyou.

 

PseudoRealityX -

Outstanding explanation!

I think every car forum has multiple threads on this topic and yours is the first understandable discussion I've read of "how it works." This was always a hot issue with the Nissan 240 crowd in that someone would upgrade their piping and then lose torque. Based on the information I've come across a 2" exhaust should be good for up to 160 HP and a good compromise between velocity and back pressure.