1991Jeep_Man

I'm getting mixed answers from the search bar to this question.

I'm upgrading the exhaust on my 91 XJ. I've already got a new APN header, and have a new high flow cat, Flowmaster Super 44 muffler, and mandrel bent 2.5" tail pipe on the way.

I think my stock down pipe from the header is 2.25" into the cat. If I am wrong please correct me. Anyways, should I also upgrade the down pipe? The stock one has this like crimp at one of the bends, and seems restrictive. Or, can I just cut out the crimp and weld a bend into its place?

Thanks guys. If it's any help, I plan to put in a bored throttle body and true CAI as well.

VTJeep

idk why the crimp is in the down pipe, but what ev's... in order for your exhaust to work at its fullest, you must have equal volumes of air/fuel/spark. if increasing the flow of exhaust, then increasing the incoming air, fuel delivery and spark are also considerations. BUT! it relative. if only increasing the exhaust volume a little, then just make sure your able to draw enough air to keep the pressure equal. the issue most ricers run into is allot of intake/exhaust volume, but nowhere near enough compression via spark and fuel pressure to keep said ricer burnin rice. like when you see one at a stop keeping the prms up to keep it from stalling...

1991Jeep_Man

So, with the soon to be bored throttle body, CAI, and the upgraded Fuel Injectors I have, should I replace the down pipe or does the crimp not cause that much of a problem?

1991Jeep_Man

I also read that there is a decent sized dent from the factory in the pipe right below the flange to the header. Should I cut this out at least?

country_boy454

You will want to eliminate any restrictions in the exhaust for the best flow/power. I dont know the size of the downpipe but I would just have an exhaust shop bend you one. Having the exhaust done first will only compliment the next mods even further! You won't have any problems with just upgrading the exhaust either.

Kyle 4x4 4life

Not to be an *** or anything, but would taking that bend out and taking the clamp out and welding it really be any bit noticable when driving? i may be wrong but i just cant see them two little things really hold your jeep back enough to waste your time/money on it.
If your looking to drag race it, then i can see getting any bit of restriction out of the exhaust, but for a jeep that will probably just get wheeled and/or driven daily, i personally wouldn't waste to much time or money on it. You have the muffer, high flow cat and header them are the three most restrictive parts of your exhaust so i'd say your good there
Just my .02

1991Jeep_Man

I much appreciate your $0.02. I don't drag my XJ (minus those few times from stop lights when the little gangbangers in their Hondas need to be taught a lesson ). Otherwise, I am strictly 4x4 and DD. I might still put a pipe in place off that crimp. But I read somewhere that it is for driveshaft clearances, so I might also just leave it be. I dunno.

Kyle 4x4 4life

Ya im sure its there for some reason, cant see them doing it for nothing.lol I hate them damn ricers, there's one here that is actually really fast(supercharged cobalt with a huge fart can) and he will race you all day if he know's he'll win but the second i get on my bike he wont even hit a straight away next to me... But one day he thought he could take me in my jeep, but there was a little snow on the ground so i threw it in 4wd and punched and walked all over that ricer i need that sticker "yours may be fast, but mine can go anywhere"

1991Jeep_Man

That would be the best sticker ever. I'd buy one. Basically here where I live, you have a bunch of wanna-be's whose mommy's and daddy's bought them Hondas and Nissans and what not. They all think they're bad and assume that Jeeps are slow. Mistake

Btw, I looked into it, and the "dent" is only about 3" long. If my physics lessons did anything for me, that type of venturi with the velocity of the 4.0's exhaust won't cause much of a hold up.

Basically, the exhaust will squeeze right there, but with the initial velocity of the exhaust stroke just a short ways away, the gases shoot right on through and equalize. It would only be a problem if the dent were much longer.

Kyle 4x4 4life

Heres the sticker...http://cgi.ebay.com/I-CAN-GO-ANYWHER...item2eb40a0f89 think im gonna order it And glad you solved that dent situation, one less thing to fix

country_boy454

Why waste your money upgrading everything else then have that bottleneck still there? More flow from the header into that crimped area will flow just as good as the stock stuff. Its like trying to breath through a stirring straw you get at the gas station for coffee vs a mcd's straw. Whats easier? Might not be a seat of the pants difference but it all adds up. I dont know about you but I want all the power I can get to keep my tires spinning in the mud. Yeah gears are great but more power with the proper gears is better.