Can you guys tell me what a good header and muffler I can use without spendind big $ I'm not worried about the s pipe or tail I can bend those myself. I plan on going with 2 1/2" exaust would that be good? it's going on my "88" 4.0 It's already got good power but I think the stock exaust is holding up the high RPMs'

 

If you're looking for super cheap, the renix's already have larger header lines than the newer XJ's, but the H/O exhaust I have that was with flowmaster tubing (and either a newer H/O cat or an aftermarket.... still working on that one) I've had a lot higher flow and it sounds great too

 

i found that the replacement manifolds are pretty much headers thats what i have on mine its a 96 4.0 HO then i run a flowmaster muffler and just ordered a dynomax high flow cat

 

Really aren't many options for us Renix guys, Pacesetter makes a header but from what I understand their quality isn't that great. Opening up the rest of the exhaust is recommended. Replaced the pipe after the manifold is recommended, its got pretty restrictive crush bends. I replaced mine with a smoother flowing pipe and the engine revs a lot easier, used to struggle at higher rpms but not so much anymore.

 

Ebay header (best automotive) is where i got mine from. Replace the cat with a highflow and a catback of your choice. but than again you have a renix.

 

You do realize the the Jeep 4.0 comes with a Tube header from the factory, it is flimsy, cracks. There is nothing in a header on the market that is going to get you any real HP. Your best bet as far as exhaust is CAT back system.. What the 4.0 needs is for the intake to be opened up, this is where the airflow is restricted. You might also consider a cam or stocking the motor.