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Header recommendation and what should follow

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Question is in regards to my LWB truck that will have a tuned up 4.0 (bored, decked, cammed) on OBDii (99XJ conversion).


When I assemble the truck I will be replacing the exhaust system because mine is rotted and the exhaust manifold is cracked.


What type of header works best with a mildly built 4.0? My only experience with a 4.0 header is with a Banks unit installed on my buddies TJ. I think he has the whole Banks system on his rig; I think its too loud for a DD even though it doesn't drone like so many others.


When replacing the header, should I maintain the stock one piece design, or should I switch over to the two piece design? I am not too concerned with the header cracking as any good one will have a lifetime warranty. Will the two piece header design work with a 99 intake/head? I know this would require the newer style down pipe (with pre cats) and would probably require relocating the O2 sensor on the down pipe where the two header outlets converge to one. Or is there any body who sells a 2 to 1 down pipe for the XJ/TJ without the pre cats?


Then onto the rest of the system. I will be retaining the cat. My intention is to reuse the 99's cat.


The next piece of the puzzle is the muffler. I am NOT wanting to know what you are running truck and how much you like it on an otherwise stock exhaust. I did read through JeepComj's thread about his muffler selection. From that thread it seems like a 2.5 in/out OEM style would be the best bet.


In Jeepco's thread Don mentioned something about inherent drone due to header designs for a 4.0 and that dual exhaust greatly reduced it. I want to run a single pipe out the back with the same routing as the stock system.


My goal? A complete exhaust system that will complement my motor, maintain the emissions equipment and not be very loud. It will be my daily driver.

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My 2 cents.


Edelbrock's six into one header is pretty nice and seems to be designed for your performance level. I like all the pipes going into one. It seems like a 6 to 2 to 1 set up would just slightly lower your powerband and increase torque mainly. While a 6 to 1 seems to help rip up through the top of the powerband.


As far as the muffler is concerned, with quality built mufflers the more noise the more flow. So just find the best balance between performance and what your ears/local police can stand.


It is possible to build more torque with more restricted exhaust system, but that direction never seems to pay as much as more open and consequently louder.


But really unless you are planning on forced induction all gains from and exhaust system are pretty minimal in the big picture.


(disclaimer: this is all based on my limited experience racing cars with inline engines.)

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Thank you for the insightful information. I am certainly not trying to build a high performance power house, I just want to realize all possible gains from the engine work I am going to get done. Plus I need to replace the system anyways, might as well upgrade!


Can you explain why a 6-2-1 header would not breathe as well as a 6-1? I am not doubting it, but I'd like to know why. Possibly the extra turns in the pipe routing?


When pulling the MJ and XJ stock exhaust systems, I noticed the down pipe was crushed right behind where it mounts to the stock manifold. Initially I thougt this crushed piece was damaged by somebody bottoming out the front end, but it was the same on both Jeeps. What might the purpose of this be?

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The header you use will be dependent on whether you use a mid 99 and up intake manifold. Example....a borla does NOT work with the 99 up intake without risky modifications to the number 6 intake runner on the manifold and the same tube on exhaust.



From what I hear, APN is a good choice.


As for mufflers....all dynomax ones are too loud. I chose a dynomax ultra flow and am ok with it...but it would be better if it was quieter.


Likewise flowmaster and cherry bombs.


Stock cat will work just fine.

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i had 2.5" exhaust on my xj with the flowmaster 50 series. to me it had a very tinny (tin) sound, once i put the banks header on it definatley made it louder and growl deeper. the header opened up quite a bit more low-mid power. my next choice of muffler is going to be a magnaflow though. they seem to be a mellow idle and a nice low growl without being obnoxious when you really get on it.


i have no experince with other headers, but i assume that they will all make you exhaust louder due to the better flow, as I'm sure you know.


edit: seems like you stated your going with an oem 2.5" in/out mufler, my bad

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Can you explain why a 6-2-1 header would not breathe as well as a 6-1? I am not doubting it, but I'd like to know why. Possibly the extra turns in the pipe routing?


Well it sounds like from some of the other posts that your header pipe configuration may be year specific.


When I was racing compact cars we used 4 to 2 to 1 headers on automatic trannied cars, mainly because it left the power band alone, and just allowed you better flow. But didn't do anything radical enough to mess up the balance between shift points and power band usage.


For manual trans equipped vehicles we used 4 to 1, because it shifts a lot of the usable power to top of the power band. I mean you had to rev the pee out of 'em to get to it, but we were anyway. You would sacrifice a little bit of torque to really tear through the top of the gears, and as long as you kept the rpms from falling too far you could definitely tell a difference.


The only exception to this was on vehicles with a "cliff face" in the power curve (meaning that you are looking at a dyno chart and its relatively level until a certain rpm and then its all the power all at once. Some engines like the Hyundai Beta engine was a super fast revving engine that tore through the top of gears like no bodies business, so the power was in danger of being moved out of reach with a 4 into 1 header, so 4 to 2 to 1's were a better choice for those engines.


To make a long story short, I thought maybe your were gonna street race it some, or maybe do some dirt drag, or maybe even some truck class autocrossing.


Hypothetically, if you put one on your truck one day, and the other on their the next your "butt dyno" wouldn't be able to tell much difference, so don't worry yourself about it. Because it really only matters if the following sentences sounds like to you would be doing. "I came out of turn 3 banging on the rev limiter in third" or "man, at the top of 2nd I was about to reach 60, and it felt like the motor had more to give, but I ran outta gear before I could get there."

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I used the APN header and a Thrush welded muffler on Onyx. It was pretty quite and had better throttle response than the stock system.


I retained the 98 XJ down pipe and cat. I needed to pick up two pieces of 2' extension pipe and four 2 1/2" muffler clamps from Autozone to make up the difference in the length from the stock muffler to the shorter Thrush. For the tail pipe my stocker was perfect and I retained it.


Questions about exhaust is just as bad as asking if Chevy, Ford, or Dodge is the best 3/4 ton diesel.


Weather you want it or not you are going to get peoples opinions on which one is the best.


BTW: Cummins FTW!!!

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FWIW I would ditch that '99 0331 head and run an earlier 0680(?) HO head. 99 was the year of cracking issues with the 0331 and the earlier head is better for performance anyway.


I thought it was the 00-01 XJ with the 0331 head issues?

Ah it looks like the later 99s had the 0331, id check and be sure anyway.

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