GearheadDon

Hi all,
I'm doing some work to my daughter 98 XJ, and I'm pretty frustrated with the big factory dent in the exhaust head pipe. Is there a easy solution to opening this up and getting better flow?

I'm in the process of replacing the Exhaust manifold, and perhaps the Intake as well, and the restrictive Exhaust manifold really is going against my intuition. I don't want to go to a whole new larger exhaust, just replace the head pipe.

Also, if I go to the 99+ intake manifold, are there other mods I'll have to do to make it work?

Thanks,
Don

PS, sorry for not searching first, I'm kinda swamped

DieselD

You could heat it and beat the dent out.

Walker makes a replacement down pipe with no dent I think.

You could take it to an exhaust shop and have them bend/make one for you. Or you could try that yourself.

Scott_Sport99

ever heard of savaging???
you will do more harm then good if not done correctly.
that "dent" is there to help with some back pressure.
it is there for a reason if you have not...
this explains it.
http://en.wikipedia.org/wiki/Scaveng...8automotive%29

MonacaYankee

Just had this done on mine. 40 bucks for a new pipe from the flange down to the crossover pipe. An annoying tick disappeared and the motor runs noticeably smoother now.

PNWjeeper

The "crush", as most people call it, was put there from factory disguised as a clearance feature. It's true purpose is to slow exhaust down to heat up the cat faster to meet EPA standards. I'll post a link in a min.

PNWjeeper

Linked post #4

https://www.cherokeeforum.com/f2/den...wnpipe-162353/

ktmracer419

Has anyone even noticed a real gain from eliminating it? I think its just extra work to please peoples poorly calibrated butt dyno's.

cruiser54

Not true. No engine NEEDS back pressure. The dent was put there to slow down the flow of exhaust gasses and heat up the converter more quickly. It was disguised by the factory engineers to appear as done for clearance for the front driveshaft. This explanation straight from a buddy at JeepTech.

cruiser54

YES. Immediately. Done 2 of them back to back.

If you have 3" or more of lift, you can just use the undented replacement pipe. If not, you must have a muffler shop make you one and route it away from the driveshaft.

Wait til you look into the pipe from the end where it's crushed. Probably 30% restricted volume wise.

PNWjeeper

Cruiser explains it better then I do.

Scott_Sport99

I stand corrected..sorry for the mis-information.

cruiser54

No biggie. You got "wikied". LOL.

Go get your downpipe done.

Scott_Sport99

didn't get wikied, used it from what I grew up with. Used to build 1/4 mile cars. everyone always said free flow on the 1/4 back pressure on the street.fastest car we built was a 6.89 sec keith black hemi Lambo.ground up.

cruiser54

Oh. I saw you had a wiki link in that post. Didn't read it....

offroadordnance

The engine is purposely run rich at start up to light the cat off on just about every new car. I dont see the dent being used for the purpose of lighting the cat off. Most likely the dent provides restriction leaving more inert exhaust gas in the chamber to reduce NOX. Other EGR delete vehicles us VVT on the exhaust only to reduce NOX by dilluting incoming charge/ reducing combustion temps. The later head castings were redesigned with more exhaust restriction. Why? probably to better control residual exhaust left in the chamber and reduce NOX more consistently than a dent, definitely not to kill power and mileage.