Climbing under the heep today I noticed the down pipe on my exhaust just below the flange has apparently met up with a foreign object (the location leads me to believe that at some point the strap kit on the front driveline let go, sending the shaft into the pipe), the result being a dent that has reduced the pipe to about 1/2-2/3 of origional size. I understand that reduced flow can lead to performance problems, but that is where my knowledge ends. I don't seem to have any loss power wise, she has plenty of get up and go. I am however getting poor mileage (I know XJ's are'nt Prius'), 11 city, 15 highway with a 3" lift and 31's and my foots not too heavy. I've searched around on the forum and compared to what a lot of people are getting with the same setup, I think I've got a problem somewhere. I thought I'd start with the simple stuff. If anyone has any expertise on exhaust and the effects of such a restriction, your help would be greatly appreciated.

 

Mine is the same way and I average about 18-20 miles to the gallon. I'm just gonna leave it alone until I can get a header and newer intake manifold

 

Cool, thanks for the quick response, I guess I can rule that out.

 

Just so you know that dent is actually from the factory,as far as exhaust goes,any thing that restricts flow from factory specs will cause poor performance and poor mileage,weather it is air filter,clogged cat or muffler,your engine is just an air pump that uses an explosion for lack of better word to keep it spinning,the more air,the more fuel,the higher the output basically,compression ratio has alot to do with it. When I have these issues I start by checking compression,to see if it is low,then check fuel pressure,air filter,etc,the only way to check exhaust for restrictions is to have a back pressure check done.
I would also think that you should have some kinda of indications,like codes. Have you adjusted your mileage for the the tires?

 

Is there a reason that you know of why they would make the dent? I've never run into that before. Yes my milaege figures are adjusted for tire size. no codes. Looks like I got some more searchin to do.

 

I would think it has to do with clearance,they have been there since 87.

 

Yea i notice that on mine when i first bought it. Eventually im gonna cut it and weld a nice mandrel bent piece in its place.

 

logged in to search the same info regarding the dimple or dent in the pipe. my 96 xj has the same thing. either a factory design or something with the install equipment that put too much stress and bent all of them the same...implies same factory line tho'..

 

It's for drive shaft clearance, and all the 4.0's downpipes have the same feature. Even the 2wd XJ's..