99+ Intake manifold

Hi all,

Alright, before I even start this I have to say I am not a newbie, I performed a search, had trouble with it because of the number 99 for some reason, and couldn't find it. So anyway,what's this I hear about the 99+ intake manifold. I know they changed them, but are peeps switching them in older rigs for performance? Is that where the 4.0 picked up those three or so ponies? I'm looking to open up the intake and exhaust as much as possible, and I like the way a better breathing manifold sounds. If this is true, does it just bolt right up, or is there trouble with the ODBII and ODBIII matching up? (I have a 94') Also, if all other answers are lookin good, where can I get one? Seems like the stealership would charge me a large one for every nut and bolt, I'd rather there was somewhere else. (Plz don't say boneyard, Ive never once seen a 4.0L XJ in any by me, especially not a 99+) And finally, thanks for reading my long ass post and answering my barrage of questions.

You'll find more information on the boards at the "strokers' egroup (link below.)

As the 4.0 evolved, the intake runners in the head were gradually and slightly straightened out, which increased airflow efficiency and THAT is where the extra power came from. Remember that an engine is little more than a self-powered air pump that makes more power than it needs to run. Increasing the extra power made is a matter of increasing the efficiency with which the air enters and exits the engine (which is the targetted result of most mods, if you look at it.)

Swapping just the manifold isn't the key, tho. You will want to think about switching the entire head assembly to get the full effect of the airflow increase. If you have an HO already, it will be easier than switching heads on the Renix (87-90) due to electronic changes carried out by ChryCo.

Strokers E-group

5-90

Kay, thanks. I havent looked at the link yet, but just asking real fast, do you think i will realize any gains form it? I do have the HO,with a bored TB, K&n, opened up intake, and cat'n'back. Im also planning on a port 'n' polish for the head in the future. So, now or later, will this do me any good?

Ironically Jeepspeed, you're question would best be answered by the guys out on the Jeepspeed forum. Several of them have swapped out to the newer intake manifold on their racer cherokee's and they have noticed significant gains with it. There is a Cherokee race team out there called Ajax Auto who runs a stock post 99 XJ and wins quite a bit. I emailed the guy (John Kearney) some days ago about this very question and he told me that every year from 97-up the XJ has gotten noticeably faster and he noticed this especially when the new exhaust and intake manifolds were introduced and secondary to that was the coil-on-plug ignition, he states that that may have helped a bit as well. Now I've been doing some research myself on the newer intake manifolds and this is what I've found: this is from JP magazine from March of 2003- March 2003 issue of JP magazine....article titled "Excellent XJ",page 28 "John Kearney of Ajax auto parts( driver of Billy Bunch's Jeepspeed XJ), swears the new intake is good for 25 hp, due to the equal length runners, where as the squared off intake has unequal length runners" shows the difference with two pics.
Here is another individual report where someone swapped out the intake manifold to the newer style: "I just wanted to tell you guys about the updated '99+ 4.0L Jeep intake manifold I installed with a self-bored-out throttlebody. I felt a slight power loss off the line but once the engine hits around 1,500 rpm, it comes alive and hits the redline much, much faster. Now, since I don't have access to a horsepower dyno I just relied on my "ass-o-meter" and felt a noticeable gain in horsepower. I installed the intake on a '96 XJ 4.0L with a K&N filter and a Flowmaster muffler. I would definitely recommend the upgrade, but I have been asked many times what the actual horsepower gain is and I can only say that another magazine rated the gains at 25 hp."
--Bryan Cloward

I'm here to tell you that with the newer intake and exhaust manifold and 2.5" S pipe the post 99 XJ's can cover some ground in a hurry especially with alot of modifications. Yes Jeep had to make the 4.0 less polluting but all they could manage was a LEV status (low emission status) with the EPA and LEV does not hamper any type of power gains in any way. HTH

Let me add that the article in my previous post: "Excellent XJ" was researced painstakingly by "Awsum98xj" I'd like to give him credit for helping me with the search but I cant remember his screen name.

Wow, Saga, thanks alot. Man, that really got me excited. 25 horses obviously sounds a little exaggerated, but the guy from the quote you included sounded happy none the less. So, now that I won't be able to sleep until I know I can get one, does anyone know where I can? I don't wanna have to start selling drugs to buy one from the dealership, and like I said, junkyards are a bust. Is there an oem parts supplier or anything like that I can order one from? Or is someone parting out their late model XJ for some wierd reason? Again, thx for everyones help.

so is the 99+ intake manifold a direct bolt up to a 91-98 head?

I think everyone is taking that quote in the wroung way. I belive when he said that he was talking about a built race motor not what kinda gains you can get just by bolting it on a stock motor. Its just like alot of mods if you keep the stoock renix exaust manifold on and stroke it and everyother mod then putting it on a dyno then change to a good header you'll see a crap load of HP come out of nowhere. Is it a better intake hell ya but don't hope for a 25hp gain.

REDXJ4FUN said:

I think everyone is taking that quote in the wroung way. I belive when he said that he was talking about a built race motor not what kinda gains you can get just by bolting it on a stock motor. Its just like alot of mods if you keep the stoock renix exaust manifold on and stroke it and everyother mod then putting it on a dyno then change to a good header you'll see a crap load of HP come out of nowhere. Is it a better intake hell ya but don't hope for a 25hp gain.

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John Kearney of Ajax Auto runs a stock XJ in the races. It would be nice to read the entire article but it's not available on JP's website. His comment is a comparison between the older manifold and the newer version.

04 Neon SRT4 dynoed @ 300hp!!

http://www.apexmodified.ca/phpbb2/viewtopic.php?t=425

Now someone prove to me otherwise that DC does NOT lowball the hp figures for either EPA and/or insurance reasons. This is a case in point only because more often than not have I seen DC undercut the hp figures for specific purposes. Another example would be the new Hemi that is going into several platforms within the next year, it is underrated in hp @ 345 in several instances. Now what does this have to do with this thread? Simple, I am almost certain this is what DC did with Jeep vehicles as well. So what if the rating of 25hp was exaggerated for the new manifold? Say the newer Cherokee is rated at 210bhp, nobody can argue that it is NOT out of the realm of possibility solely based on all the "upgrades" done to the 4.0

"Jeepspeed, the mach 5 is not ready for that much horsepower, haha" "you'll have to use the cherokee, haha"

sorry, couldn't resist.

First off, sorry everyone, I prolly shouldnt be posting right now, cuz im wasted. but Maasbay, I sorry, i had no idea what u just said. If it was an insult to supin up a jeep, ford sucks man, and what's wrong with makin a 2900lb sleeper with 50/50 weight distribution? If you didnt mean anything like that, sorry. But either way, I'd still like to throw a newer manifold on, if it gets me 3 horsepower or 50. ALso, before I hit the bars=, does anyone know another place i could snatch one? I've checked Ajax multiple times, and it always says there are no matching parts. Any input(even negative) is appreciated. Muchos gracias.

Oh, yeah, and Saga, thats 100% right. One of the reasons i love DC is because they almost alway deflate thier hp and torque numbers. Most other makes inflate 'em, but jeeps and dodges almost always dyno higher. Understated champions.

JeepSpeed said:

One of the reasons i love DC is because they almost always deflate thier hp and torque numbers.

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DC correctly rated the HP numbers of the 4.0 but they did underrate the torque by about 15lbft. The early HO 4.0 XJ should have been rated at 190hp/240lbft and the later one slightly higher, but definitely not 210hp. A '00 XJ is not quicker than a '92 XJ so I think the 210hp claim is just wishful thinking.
As for other Jeep engines, DC correctly rated the 4.7 V8 for HP and underrated it for torque, underrated the 5.9 V8 for both, and correctly rated the 5.2 V8 for both.
They didn't underrate every engine though. They somehow managed to grossly overrate the 3.5 V6 in the Chrysler 300M. They rated that one at 253hp but the performance suggests that it has about 30hp less than that.

JeepSpeed said:

First off, sorry everyone, I prolly shouldnt be posting right now, cuz im wasted. but Maasbay, I sorry, i had no idea what u just said. If it was an insult to supin up a jeep, ford sucks man, and what's wrong with makin a 2900lb sleeper with 50/50 weight distribution? If you didnt mean anything like that, sorry. But either way, I'd still like to throw a newer manifold on, if it gets me 3 horsepower or 50. ALso, before I hit the bars=, does anyone know another place i could snatch one? I've checked Ajax multiple times, and it always says there are no matching parts. Any input(even negative) is appreciated. Muchos gracias.

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JeepSpeed, I'd at least send ajax an email they'll be able to assist from there. BTW, that 3-5 extra hp that Jeep claims is from a newer H20 pump and coil on plug ignition, there is no mention of addt'l hp from the new intake/exhaust manifold but here is a quote from their literature: The new intake and exhaust manifolds enhance the sound quality of the engine and produce a lower, "throaty" sound preferred by customers.

You be the judge on what that last statement meant to indicate.

Semi OT: 300hp on the SRT-4 !! (outrageous)! Plus it's 300lbs lighter than a WRX STi. That is insane amount of power.

i'd deffinatly change out intakes just for the heck off it. and have fun.heres where i found some here http://car-part.com/ for about 35 bucks.

I don't think the exhaust manifold would give any benefit since they switched from a tube stlye headerish manifold to a cast manifold.

CW. said:

I don't think the exhaust manifold would give any benefit since they switched from a tube stlye headerish manifold to a cast manifold.

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The newer manifold resembles a shorty header version of the Borla header for the 4.0's. Matter of fact I know a fellow street jeep enthusiast who installed a banks header on his 00 XJ and noticed very little to no improvement. He still ran a 14.7 @ englishtown raceway a few months back.