Hey guys I have a 91 xj 4.0ho and I'm beefing up the air flow. I already have pacesetter long headers and a thrush glasspack. I don't know which free flow cat I should get and which cold air intake. I'll also be getting a BBK 62 mm throttle body. What should I get to go with what I have?

 

Look into boring,your tb it's probably cheaper, look into injector swaps 99 intake....Also make sure tune up related stuff is up to date

 

You're going to want to get a new downpipe (the pipe between the exhaust manifold and catalytic converter) as the crimp found in most stock ones isn't doing you any good. However when you replace it be sure to securely hang the new one from the same rubber mounting point the old one hung from. Its gonna be a PITA but trust me, you don't want that pipe rubbing the crossmember and vibrating horribly. Guess how I know?

Don't waste your money on a "cold" air intake, throttle body spacer, etc. What will give you real gains is swapping your intake manifold with one from a 1999+ Jeep XJ. Doing a cowl intake mod (forum search that) might actually be worth it in terms of performance, plus it moves the intake higher, and collects loads of enormous dragonflies in the air filter which is interesting.

 

Well my headers go all the way to the cat and I ALSO have the exhaust rattle on my crossmember lol I was looking at cold air intake because the stock air box is VERY restrictive so I was thinking some kind of better induction. And I still don't know which brand cat would work well for what I got

 

A 99 intake will be a good upgrade as well as a downpipe from the same year, a "Walker" brand is a good choice.

I cowl intake works as well as anything and better than most when it comes to cool air intake at base of windshield. A screen is used to keep larger things from the filter that is under the hood not at the cowl.

 

A cowl intake will be the best cold air option. your header goes all the way to the cat? What? Ya sure?

 

My headers are 6-2-1 and the pipe goes all the way to the square flange that holds the exhaust above the crossmember.

 

did you have any trouble with fitment? how long ago did you order that header? painted or ceramic coated?

 

Getting the last bit of the pipes together was a bit tricky but that was my fault on a stupid simple error but once they were in place the whole thing sat nicely besides over the crossmember. I got it little under a year ago and it's aluminized steel with a black painted coating that lasted maybe a month before completely peeling off

 

it says the black paint is for storing/shipping only. I was about to ask if it hit your intake manifold but I guess it doesn't matter bc you don't have a 99+. what did you have to do as a remedy for the crossmember interference? I'm assuming the header itself doesn't leak where the joints are. thank you for answering my questions.

 

Unfortunately the rattle is still there but I bent the hanger up just a little bit and it made it a little quieter. When it's cold outside the rattle is pretty loud

 

Ive got a TB for you that's a lot less than a BBK....but its 60MM.

 

That would be nice but I'm pretty sure the tb is already 60mm. That's why I was shooting for the 62. I don't know anything about boring out the throttle body

 

i think its xjfiles will bore them out to 62, and io think theres another on here...

 

Unless someone bored it...the bottom is 55mm.