'98 XJ 4.0L benefit of headers?

Hello, group - While crawling under my XJ 4.0L, I have been amazed by the degree to which the downpipe from the exhaust manifold is collapsed. It is 2/3 shut at the bend.

I have mentioned this at both the local 4WD shop and at the dealership parts counter, and the replies have been something to the effect that "Those 4 Litres seem to like the restriction", to "That's normal. They're all formed like that".

When I read about modifications for power, those most popular seem to be (not necessarily in their order):

  1. Replace cat-back
  2. Headers
  3. Bored-out throttle body
  4. low-restriction intake

What do the experts on this board think? Does this engine really benefit from headers,since it seems as though it was engineered for significant back-pressure?

Thanks.

jim

Reply to
98XJ
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The 4.0 in my opinion has quite a bit of power for a V6. But I would also like to find out some little mods to get some edge

Reply to
abomb69

Reply to
98XJ

Well when I had a custom straight pipe with a high flow Dynomax Turbo muffler put on my CJ7's 258, they did a smooth bend instead of the kink bend that was there on the downpipe and I sure thought I got a power increase. I also think I got 2" pipes.

It sure sounds nice anyway....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06
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Reply to
Mike Romain

Reply to
L.W. (Bill) Hughes III

The XJ 4.0 IS the inline 6, not some weenie V6 .

Jeff DeWitt

98XJ wrote:
Reply to
Jeff DeWitt

Thanks for correcting me...But either way the inline 6 has quite a bit more power than most V6s I've ever owned including the 4.3 GM

Reply to
abomb69

That's because it's a better engine .

I've really embarrassed a few Mustang drivers with my little Cherokee, that sucker is pretty fast. I expect that above 50 or so a Mustang would pull away but in one of those little stoplight contest I'm not going any faster than that... I'm no idiot and don't want to lose my license for something as stupid as racing.

Jeff DeWitt

abomb69 wrote:

Reply to
Jeff DeWitt

I have to disagree.. I find mine slow. It has pleanty of torque, but as far as gettin on the freeway or passing a car I have to pray for a tailwind and half a mile of clearance. Not to mention a gas GUZZLING 14-16 mpg! HFS! I would definitely like to find some power in this little rig. Of course, I went from a Mustang Cobra Convertible to this - so my judgement mignt be just a little clouded that got 18 mpg with my foot in it all of the time.

When it gets old and the engine finally dies, I am planning to transplant a Chevy 350 into it I think.

But, I love myJeep, and wouldn't trade it for anything. I think it's the most fun you can have with your cothes on.

Kate

2O|||||||O6 Rubicon
Reply to
Kate

To the original poster, the 4.0L is a I6, not a V6.

Kate, the vehicle will rust/fall apart before the engine dies! I can't speak for the '06, but my '92 &'97XJ have getup and go. No problems getting up to cruising speed, or passing vehicles on the road, even with 31"x9.5" Swampers on them!

E
Reply to
eric

You'd probably notice a significant power increase if you took those three cylinders that have been twisted out of alignment and move them back so your 4.0 is a straight six like it was intended.

The cat back does seem to help a bit with mileage. Crunched pipes are never a good idea and should be replaced no matter how many myths there are about "liking restrictions". If you go much beyond a simple cat back conversion, say to headers, you might need to worry about improving the fuel injectors to avoid running lean which can also cause nox failures on smog tests. Not that headers are a bad idea, just that the combo of header and cat back can improve air flow enough that now you are looking at higher flow injectors and possibly a bored throttle body. By that time, might as well consider stroking it.

abomb69 proclaimed:

Reply to
Lon

It has more apparent power mostly because it has such a flat torque curve and develops a real goodly amount of torque even at idle rpm. Torque is what gives you the kick in the rear feeling and is what most often wins the stoplight sprints to 30 over vehicles with far more actual power but not nearly as good low end torque. It should be able to climb gentle hills at idle rpm and on a flat surface with the auto, it should be able to upshift still down at idle rpm. The other end of the curve is that rpm much over about about 3500 is a waste of time and a lot of noise for nothing.

abomb69 proclaimed:

Reply to
Lon

OP here. Thanks, Lon for the on-topic reply. For the record, I am aware that I have an I-6, that was someone else opining about hos V-6.

Since my first posting, I stopped by a muffler shop where I was told tha all OEM tubes come with that formed indentation n in the down pipe, and that I am one among many to have asked about that.

It bothers me enough that I may have that section replaced with a fully-round piece - and consider a cat-back.

Thanks aga>

Reply to
98XJ

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