2.5 pipe from cat-back

[komanche]

guys, i know this exhaust pipe size has been asked over and over, but my question is what if you stay stock (2.25) from the front to the cat and run 2.50 from the cat-back. haven't seen this asked in forum and was wondering the gains/losses so thought i ask. thanks for all input.

[Eagle]

You are describing a typical "cat back" system. That's what I had on my '88 Cherokee. That's the setup I grew to hate and had a mini celebration when it rusted out so I could justify going back to the stock 2-1/4" system.

 

Loss of low-end torque, reduced driveability, loss of 2 to 4 MPG fuel economy ... but it sounded great.

 

Keep in mind that stock is not 2-1/4" in front of the cat. The exhaust pipe (or "down pipe") is 2-1/2" and the stock cat has a 2-1/2" core. The cat outlet necks down to 2-1/4" between the cat and the muffler. So by installing a 2-1/2" cat back system you end up running a 2-1/2" system from the manifold to the end of the tailpipe.

[komanche]

Eagle, can you just use the free flow muffler and use 2.25 pipe or does that negate what gains the muffler is suppose to give?

[Eagle]

Dunno. I hever felt any reason to try that. After experiencing the losses created by a freer-flowing exhaust, I decided the factory engineers did a decent job optimizing the system and I have used OEM replacement parts ever since.

 

Besides, the OEM repacement mufflers from AutoZone carry a lifetime warranty. Unless in a moment of temporary insanity I decide to try another turbo muffler, I won't be buying any more mufflers for as long as I own the two MJs and the XJ for which I have paid once.

[SoloCamo]

Eagle, can you just use the free flow muffler and use 2.25 pipe or does that negate what gains the muffler is suppose to give?

 

Yea, you can pickup a Dynomax Super Turbo muffler with a 2.25" in/out diameter for about 45 bucks from Jegs.com

 

I've heard only good things about it, and it doesn't have that nasty flowmaster drone. Just slightly louder than stock with a nice grumble, but when you get on it, you know it's not a stock system. Not over the top by any means though. Performance numbers have been proven as well and just running a free flowing muffler and cat without 2.5" piping won't result in low end torque loss. :D

 

I'll be picking up a setup like that soon