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Just another Intake Swap opinion

H

herrhefler

NAXJA Forum User
Location
phoenix
I just swapped out my intake on my 98 XJ....From a 99 XJ (New Design), and before doing so, I have read many threads on this matter and got different answers from: 20hp increase ~to~ lost fuel economy!

Well I took the plunge, swapped out my intake when I was replacing my cracked exhaust manifold....with a factory style replacement (with the little expansion bellows on it)...both cost $50.00 at a local u-pull-it!

My XJ is mainly stock, just a K&N panel replacement and a MOPAR factory catback exhaust. Nothing else was changed out in this swap.

First off...its not as hard as people made it out to be....it took me 3 1/2 to 4 hours and that was taking my time and making a new AIT pigtail and vacuum harness!

All-in-all, I haven't felt that much increase in HP....I can say it expands the torque curve out over the RPM range...it really dose seen to breath better!
As for fuel economy....so far the needle has hardly moved...I'll run a few tanks of gas though it, do my calculations and post my results :exclamati
 
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The HP improvement is good to know. I need to do the same to my XJ when I return to the US.
Did you use the injectors that came with the '99 intake or those from the older intake?
 
No techno1154, I used all my 98's original parts...just the intake and a new exhaust manifold was changed out....and like what I said, no real hp increase just seems to shift the torque band through-out the rpm range.
 
herrhefler said:
Well its been a few weeks now and I can say there is a loss in fuel mileage....
I went from 15~16 to 13~13.5:bawl:
Click to expand...

Could you be on the skinny pedal a bit more than usual?
 
Nope....got on it the first week to see if there was that much "power " changes, but after that its been almost 2 months of my "normal" driving.:dunno:
 
herrhefler said:
Well its been a few weeks now and I can say there is a loss in fuel mileage....
I went from 15~16 to 13~13.5:bawl:
Click to expand...

Pete Trasborg (SP?) from 4-Wheel & Off-Road did the 99 intake swap on his 98, and lost fuel milage as well. Others see a power increase... I wonder if it's related to Renix vs OBD I vs OBD II. I have noticed (others have as well) that the newer, OBD II, engines don't respond to add-ons like the older Renix & OBD I engines.

Do you have any other modifications I've been too lazy to look up? (Cold air intake, cat-back exhaust, bored out TB, one of them 'Tornado' air spinners, skull skift knob, etc...)

:)
 
It's basically stock....I have a K&N replacement filter and a Chrysler Cat-back system. Both have been on it for years and I got 16~ish mpg.

I double checked last week for vacuum leak, checking the lines and spraying throttle body cleaner up and down the intake.....I just don't see a leak.

...maybe it true the Renix & OBD I engines would respond better...luckly I saved my original intake and hardware!!:banghead:
 
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Well, I agree that OBDII isn't as tolerant to changes/mods, as it will end up throwing codes rather quickly when it encounters data out of programmed ranges.
 
i did this swap on my 87 renix, with an apn header at the same time. the throttle body on the 99 intake is much larger than the renix unit, and the 99 intake and apn header obviously flow better. but i was surprised how much of a difference it actually made. its cammed and has stiffer valve springs, so it probably needed better flow to begin with, but now i can climb hills that itnever could before. I was impressed. just my $0.02
 
For what it's worth, I did this swap on a friend's XJ at his request while he was on holiday... I'd read the Jp article and have even thrown it into posts like this myself, saying to save the time and money. However, he was insistent and paid for the beer and pizza so I went ahead and did the swap for him. Not unexpectedly, it got the same torque curve improvement and loss in mileage.
After some research and poking around, we stumbled across the write-up on GoJeep's website (http://go.jeep-xj.info/HowtoIntakeManifold1.htm). Swapped over the newer injectors and found a used Hesco adj. FPR (new one was pushing $180...). Definitely made a difference, which I wasn't expecting at all. Like a noticeable, obvious difference. Mileage is up a bit as well, but barely.

Just throwing that out there....
 
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So, not a very economical upgrade. It would be interesting to see more before/after dyno HP numbers.

I wonder if Mythbusters needs an episode idea?
 
XJPhoenix said:
Pete Trasborg (SP?) from 4-Wheel & Off-Road did the 99 intake swap on his 98, and lost fuel milage as well.
Click to expand...
Transborg, and he is a member here ( I have a wiring harness sitting in my garage waiting for him lol).

The fuel mileage loss is due to the increased volume of air/fuel moving through the system. Seriously, did you expect to put a higher flow intake on your engine and use less fuel :confused: As the years went on, Chryco upped the HP and TQ numbers various ways, to get the same performance out of the aging 4.0 while more and more smog equipment was added due to federal regs.

Basically, you'll get a minimal increase in power from the swap, but at the cost of some economy points - just like any other performance mod. :dunno:
 
I did the swap as well, changed the pressure regulator to a hesco and put the newer injectors in. It will power brake with
out a blink.

Mileage.... Lol I drive a xj, if I wanted mileage I'd buy a deisel engine and swap it. But I can't justify 4-5k for a swap. So I'll burn the hydrocarbons until the wheels fall off or the wallet goes flat.
 
I did the 2000 intake with APN header to fix and upgrade at the same time, hi flow cat and muffler. I love it and didnt see a lose of mpg in my 95. Well i did lose mpg overall but idk what to contribute that to, intake, 4x4 conversion with ax15, 3.07 to 3.55, locker? idk but i still get 20 mpg every tank with mine and i didnt wast much time in between mod to really calculate the mileage.

What about neon injectors? plug right in and have 4 nozzles than the single one XJ's have which means better atomization. This while gain hp and possible mpg.
 
I have also done this swap (2000 intake with an APN header) and have no loss n fuel mileage and power but I also have supporting mods as well (tb bore, cai, borla catback/highflow cat DUI firepower ignition
 
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