I can't find a straight answer to this question. I am in need of a new exhaust system, minus the header (mines a 99 and in good shape). The muffler has rust holes so it needs replacing anyways. I'm up for changing anything from the downpipe back.

I'm looking for straight MPG improvements overall. I don't care if it sounds like a prius or not, lol (hopefully not!) I've read mixed reviews on whether or not to go with 2.25 inch clearance or jump to the 2.5". Some have said that that much clearance reduces back pressure thus decreasing fuel economy. I'm at a loss people, which is the correct answer? Also, any specific links to parts would be helpful.

 

Assuming you have a 4.0L, 2.5" everything, get rid of the crush, high-flow cat and muffler. http://performance-curve.com/ has many of the parts and is a Cherokee Forum-supporting vendor.

If you have a 2.5L, don't bother.

If you have a 2.6L or 2.1L TD, swap the engine.

If you have a 2.5L TD, a 2.5" pipe with high flow muffler should be good. Don't do stacks on an XJ.

 

Its a 4.0. Didnt even realize they made 2.1 liter xjs. Are stacks the exhaust that comes out the top?

 

I replaced mine with 2.5" and put a nice flowmaster on it. Sounds great but I didn't notice any fuel savings. I wouldn't think "back pressure" would be an issue. Unless axel puts a banana in yo' tailpipe, then it might not start

 

Yup 2.1L Renault turbo diesel was mid-'80s in North America and until about 1994 in export markets. I listed all the engines since you didn't specify yours. I'm on the app so can't see signatures or profiles.

And yes stacks are the big pipes that come up in semi trucks.

 

Dang those are the best prices I've ever seen. Thanks for that post!

 

Yeah I know. Wish they'd ship up here lol. I need some new exhaust bits!

 

Same here. No improvements.

 

We went straight thru 2.5" Magnaflow all the way back, if u get my drift......a slight improvement in performance and mpg at best. I'd be leary of any advice that says reducing back pressure also reduces performance/mpg.

 

Back pressure is an inherently bad thing. However, exhaust scavenging - which what happens when a system is tuned to actually increase flow, sort of like siphoning liquid - is beneficial.

 

Just did a rusty s off road muffler and tail pipe 2.5 deal to replace my stock 200,000 mile ex. I like the cherry bomb a lot . No resonance at cruising speed.

P.S. I have all 3 cats in place so that might mellow the cherry bomb alittle.

 

Ummm an NA engine can be hurt by over scavenging . I've had this conversation with a few folks they think a 2.5 cat back is over kill on a 4.0 .
My retort is open the intake and the exhaust up and let her breath !

 

Going from 2.25" to 2.5" is overkill???? I think I'd be leary of advice from those folks as well.

 

Back pressure is needed unless you have a big ol lowpy cam. I know this for a fact. If you want to prove this to yourself unhook the exhaust from the header and take it for a quick spin and you will see what a gutless wonder you have without it. Sounds mean as **** but that's about all.

I've done a lot of research on this as I am too in the process of upgrading my whole exhaust and it appears that a 2.5" exhaust with a good muffler (like a super 40 or 44 flowmaster) and a high flow cat will net you a little bit better performance and 1-3mpg increase. So is it worth it? I say it is based on my research. But hey that's only what I have read myself. Won't know for sure until I do it myself.

 

...what? Your post makes no sense. Open it up, but even a 2.5" cat-back is "overkill"? Did you proofread this? lol What is this "over-scavenging"? Is that when the exhaust velocity is so great you suck the valves right out of the head?

This is not back pressure. This is exhaust velocity.

Some reading that applies to almost all engines.

http://www.roadstarraider.com/index.php?topic=6767.0
http://forums.mightycarmods.com/show...why-it-s-wrong

Beats me where people come up with this stuff... somewhere between lawn mowers and Cracker Jack boxes