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5.9 ZJ air intake

9K views 25 replies 9 participants last post by  OlDirty 
#1 ·
I've been researching and surprise, I'm finding all sorts of differing opinions on the net. I've got a 1998 5.9 ZJ limited with 197,400 miles. Should I pony up for a K&N FIPK, do a cowl air intake, or just keep the stock setup?

I'm leaning towards doing the cowl intake.Because I think it's a colder air flow and cool. Or, I'm just going to keep stock trim the drip tray.
 
#2 ·
OEM system with a Dodge truck air hat. Truck airhat will flow better, but needs a bit of clearacing on the hood insulation and some of the stiffeners.
Air intake is behind/ next to the front headlight, so it's sucking in cool air anyways.
K&N FIPK is a total waste of money for a bit of bling factor.
Cowl intake is good if you need it for water clearance.


People often move the intake air temp sensor from it's stock location on the kegger to the air intake tube. Dunno how well it actually works, but it should provide a more accurate intake air temp reading.
 
#3 ·
I was thinking the same thing about the K&N. It looks basically the same as stock but with the cone filter. I'm going to have to see if my local salvage yard has that truck hat. That's a good idea.
 
#10 ·
The drawback is the 3" ducting that the trucks use. The K&N is bigger and is designed to help the motor breath better. So you end up with a 25+ hp gain at or near WOT with the FIPK.

The problem with the FIPK is the seal is not positive at the TB, so you risk an air leak, thus sucking in dirt and trashing your beloved Magnum V8. The stock airhat is steel reinforced and will never leak. The FIPK has no reinforcing and you never really know what kind of seal you have at the TB. The motor moving around and the FIPK making contact with the hood delivers an unknown into the equation. A massive design oversight.
 
#4 ·
Here is a cowl intake that I just did. I actually love it. Seems like my mpg went up about 2mpg when cruising on the freeway. Its a K&N filter (RU-3130).

I had to take the hood off. After getting my 90 elbow in place I used bondo and filled in the gaps around the hole and painted it. I want to keep the hot engine air in the engine bay and so I made sure the hood rim seal stayed intact. The thin plastic tube on top I am going to cut an reroute eventually. There was minimal trimming on the hood, just trimmed off the initial step as wide as the air hat, but didn't need to trim any of the stiffeners braces (it is important not to cut past the point on the hood where in contact with the hood seal).

 
#5 ·
Why is it that everyone who does this cowl mod hacks a huge hole and has to info or fill gaps.

This is a much easier and cleaner solution and a roll of gasket material would make a nice seal and clean install.

http://m.ebay.com/itm/191129493642?_mwBanner=1

EDIT: Just buy two of them and sandwich the firewall between them. Run through bolts through both flanges and mount a silicone 90 on the cowl side, hook up the air cone and away you go. You may need a 4" piece of pipe between the air one and a silicone 90 but imo better looking finish and job that a gaping hole with an elbow stuffed through it all caulked or bondod to ****.
 
#7 ·
Nice thoughts.. I want to see you try your own suggestion and let us all know how it worked out perfectly for you. You may find that part of the sweep of 90 elbow almost needs to be in the cut hole area. A perfect circle does not work. This mod is not for the faint in heart and is not as simple as it may appear. Clearances must be exact. I see you are not a fan of bondo, but I thought my install was one of the cleaner ones that actually created an impermeable seal separating the cowl area from the engine.. unlike the other writeups I saw.
 
#6 ·
^- I've been wondering about the same thing as well. Having a bulkhead fitting go through the cowl plate and a couple removable rubber elbows makes engine work much easier as well..
 
#8 ·
I've seen those cowl ones while searching on here. It does look cool and probably sucks more col air. I'm just nervous about water getting in or snow/ice reducing airflow. Have you had any problems or concerns with it? I live in Iowa and we some rain but I'm worried if it snows or freezes at the base of the windshield it won't get as good airflow.
 
#9 ·
The filter protector "Filter Wears" is supposed to keep the water off the K&N Filter. I have only had mine installed for a week. So far I love it. I cut my plastic cowl cover in half so it would be easier to access the air filter. You have a good point about the snow in there. Snow can't fall directly on the air intake as it is covered by the plastic cowl cover, but if snow were plugging up the breather areas, it may try to suck snow in toward the air intake. Additionally, it would be good to be cautious of the snow melting and re-freezing in the cowl tray. I park my ZJ in the garage, so its not too concerning to me.
 
#11 ·
IIRC dyno tests have shown very little HP gains with the K&N FIPK on these engines. Naturally aspirated 408 stroker engines use the stock style air intake with no problem with airflow.
5.2/5.9 OEM throttle body is the limiting factor anyway, then the cylinder heads.


Btw., if anyone is thinking about modding the kegger intake runners - do NOT do it!
Flyin' Ryan has dynoed that mod, and you will actually loose serious horsepower and torque in the midrange; no gains in low- or high end. It is an absolutely unnecessary and pointless modification.
If I had only seen those dyno numbers before I did my plenum fix and modded the kegger about a year ago :rolleyes:
 
#12 ·
IIRC dyno tests have shown very little HP gains with the K&N FIPK on these engines. Naturally aspirated 408 stroker engines use the stock style air intake with no problem with airflow.
5.2/5.9 OEM throttle body is the limiting factor anyway, then the cylinder heads.

Btw., if anyone is thinking about modding the kegger intake runners - do NOT do it!
Flyin' Ryan has dynoed that mod, and you will actually loose serious horsepower and torque in the midrange; no gains in low- or high end. It is an absolutely unnecessary and pointless modification.
If I had only seen those dyno numbers before I did my plenum fix and modded the kegger about a year ago :rolleyes:
Interesting. He's dynoed intake runners and compared numbers but he can't tell you anything about the gains on his canned tunes he sells?
 
#17 ·
He is not giving any specific horsepower or torque gain numbers on the canned tunes, because there would always be those idiots who start crying "I only gained 15 horses when you said 20-40hp in most cases".
There are enough variables even on a stock engine (it's condition/ amount of wear, basic maintenance parts that have beenxused, etc.) that you just can't give any numbers.

FRP has done prpbably thousands of tunes on different vehicles, and he has done hundreds of custom tunes, dynoed them before and after to see what needs to be done, etc.
And yes, he has dyno-tested the difference between an OEM kegger and mofified kegger on an otherwise stock engine.

Heck, he even organizes dyno days where he's at a certain location for a day or two, and customers that have his tunes bring in vehicles that will get a fine-tune after dyno runs for those last few horses.
There aren't too many highly reputable guys like him in the USA that have done that with Jeep/ Dodge jtec- based PCMs. He is not the only one, but one of the very few who can actually do it well on these vehicles.
 
#18 ·
I don't have any complaints about his tunes, I just wish I knew what I had.

The first gen K&N had a huge airhat. That's the one with the one hole in the middle. Somewhere along the line, they reinforced it with a large metal ring inside the neck, taking away tons of flow. Those are the 2 hole ones.
 
#20 ·
In my opinion, the fipk is a huge waste of money for something that makes more noise, allows fine dust particles into the motor dirtying the oil faster, is ill fitting, is not cold air, developes crackes over time, seal on TB is garbage, and dies not add hardly any hp.
Its also a pia maintenance with cleaning, "naturally drying it", and recording oiling "properly".
This is a great filter for race applications where the motor is constantly bring rebuilt and can take advantage of the almost non existent filter media.

The stock air box sucks cold air, has a paper filter which is more than adequate for any motor not tuned, not force inducted, cam editor or stroked. So if you're stock then please font buy this first.

The main bottle neck on the stock air intake is the air hat on top of the throttle body. Is restrictive.
Summit sells some stuff or you can find a Durango air hat at a junk yard but you'll need to modify the hood a little unless you find a way to clock it because it's taller with an angle.

I got my Durango hat at the junkyards for 10 bucks.
That's well worth it.

Now having said that, I have a k&n fipk for a 5.2 or 5.9 for sale for 60 bucks plus shipping.
 
#22 ·
Looking at pics it is kinda hard seeing where the intake is being cut through the firewall. Looking at my firewall I see a bunch of crap in the way, mainly the coolant res, heater lines, and random stuff.

With that being said, for work I do custom sheet metal fabrication. I have a roper Whitney 3 phase shear that can't cut 10' widths, and a roper Whitney CNC auto brake.

I just made a custom wind diverter/sunroof visor yesterday out of .040 aluminum (so it don't rust)in black metal. Fits and looks really well, as well as works very well. It's mounted to the front roof rack bar. So that's not really movable anymore. I'll just get another one from the junkyard and put it up there. So I'll have 3 rack bars total and still have 2 functional ones.

I may make a firewall mount box. That way the hole can be cut for a standard 90* elbow and you won't have to worry about its cleanliness and sealing. Then the box can be sealed and mounted to the firewall and give some extra depth allowing those MAF adaptor sandwich plates to be used as well.

Give me a couple days (over the weekend) and I'll try and get something fabricated up and started. I'll post an updateor make a new thread with the progress and info. And if anyone is interested in one I could start making them, or start selling a cowl intake kit for the zj.

What I do need an answer on is if the firewalls on the pass side are the same or similar enough on a 4.0 and a 5.2/9 so it can be a universal firewall kit. All that would be required is the filter of preference and the air tube.

I could also make some sort of air filter rain hood that gets mounted in the cowl over the filter after install to help with the water issue. It will be a removable part so the filter is serviceable of course.

Lmk if that sounds like an idea or kit that anyone would be interested in (would give me some extra motivation to actually start it), and the 4.0, 5.2/9 firewalls are similar.
 
#23 ·
Yeah, the unibody it identical 4.0 to V8.
 
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