Differences in stock airboxes (write-up)

Dunno if I can call this a write-up but I got bored so I figured I'd tap into my wealth of useless information for anyone that cared. I've had (I think) 3 of the 4 different "models" of airboxes in my 1990 4.0 XJ. Here are some of the differences.

1987-1990-these have the ports for the CCV and charcoal canister as well as two small ports at the back. One of the small ones controls the motor for the door at the front of the box and the other one IIRC is tied to the emissions system. They also have the port at the front for the preheater tube running from the exhaust manifold. Wire clips are used to hold the lid onto the actual box itself.
1991-1995-the two small ports were deleted at the back as well as the preheater tube port and the motor/door at the front. The charcoal canister port also was moved up closer to where the air tube from the throttle body connects. Metal clips and tabs replaced the wire clips to hold the lid onto the base.
1996-I think this one existed for a year, I may be wrong and in 96 it may have been the same as 97+ units. The charcoal canister connection was deleted because it was moved directly to the intake manifold. The CCV port was moved to a more straight across position from the front CCV fitting on the valve cover. The thing is...I believe the air induction snout that pulls the air in was still long for the old body style. I'm not all too sure on this though.
1997-2001-for this year the intake snout was shortened for some reason. I have no idea why but I'm currently using the base of this airbox with the lid of an older one. The snout falls about 1.5" short of where the old ones protruded through the front body brace (or whatever that is) and is diagonally cut. I assume in 97+ XJs they must have moved that brace panel back for some reason (again no idea why) that's why the change was made.

As I mentioned earlier, I'm using a 97+ base with a early HO lid. I have the 97+ lid so I eventually plan on routing the charcoal canister directly to the intake manifold.


Some other things to know...
1. Any air box base will physically bolt up to the floor of the engine bay.
2. Renix air boxes will not work (without modification) to the HO models and vice versa.
3. If you move the charcoal canister line directly to the intake manifold you can put a 96+ lid on an earlier HO base.
4. With a GDI open system radiator they all have trouble fitting and clearing the filler neck.

Those two vacuum connexions on the back of the top of the RENIX airbox are for the TAC (Thermostatic Air Cleaner) that was deleted with the introduction of the HO engine.

One side is connected to a vacuum source (manifold vacuum,) and the other goes to the door at the airbox snout. It does not matter which hose goes to which port - it's not a one-way valve, it's just a thermostatic valve.

Also, there is a "venturi insert" in the other snout off the top of the airbox (going to the intake manifold,) which is meant to assist suction for the CCV. This venturi insert may be removed to effect a slight increase in airflow before the throttle body - I haven't quantified this yet, but I have noted a slight increase in throttle response with no other modifications done.

I'd have to dig up my notes to see if anything else should be added, but I can't think of anything else offhand...

5-90

5-90 said:

Those two vacuum connexions on the back of the top of the RENIX airbox are for the TAC (Thermostatic Air Cleaner) that was deleted with the introduction of the HO engine.

One side is connected to a vacuum source (manifold vacuum,) and the other goes to the door at the airbox snout. It does not matter which hose goes to which port - it's not a one-way valve, it's just a thermostatic valve.

Also, there is a "venturi insert" in the other snout off the top of the airbox (going to the intake manifold,) which is meant to assist suction for the CCV. This venturi insert may be removed to effect a slight increase in airflow before the throttle body - I haven't quantified this yet, but I have noted a slight increase in throttle response with no other modifications done.

I'd have to dig up my notes to see if anything else should be added, but I can't think of anything else offhand...

5-90

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Please do add anything more if you have it, I was drawing blanks on those bits since I haven't had the stock RENIX one in there for so long. And I forgot to add I always remove the venturi as well. I've never felt any great improvement but if nothing else it just looks like it's getting more air that way. Also, when I said ANY airbox will bolt up, I mean any XJ 4.0 airbox.

On the RENIX models...Can the charcoal canister connection be moved to the intake as well?

I'm also running the newer style bottom with the RENIX top, I've deleted the TAC all together.

I'm thinking about putting my MAT into the rear of the airbox(remove the TAC valve and drill a hole there). I think it would give the computer a more accurate air temp and it may run slightly richer in the winter. Anybody else done this? Any major mileage changes?

Sorry I can't add anything but this is great info....of the kind you won't find anywhere on the net!.........Thank-you.


-Ron

xjtrailrider said:

On the RENIX models...Can the charcoal canister connection be moved to the intake as well?

Click to expand...

I'm not going to say one way or the other for sure but technically mine is still a "Renix" model and I'm going to move it. I've also got a 99+ intake though so it has the port where those model year's canister connected directly to the intake. I imagine on yours you could just get a vacuum "Y" or "T" splitter and just plumb it off the charcoal canister into the splitter. Whether it will work as well as straight from the airbox I'm not positive.

XXX said:

Sorry I can't add anything but this is great info....of the kind you won't find anywhere on the net!.........Thank-you.


-Ron

Click to expand...

Ron, thanks for the thanks. I figure even if this isn't a topic that many people are concerned with, if it helps those who are in need and will search, I'm glad I could help. You're right though, it is such a random topic I doubt anyone else has written on it.

A small side note for the Renix airbox bases: you can toss out the hoses and vacumn motor for the "flapper" in the snout, silicone the "flapper" over the hole left after you trim off the snout to a stub, and then relocate the opening to the back of the box for a REAL motor saver, incase you ever hit the WRONG spot during a water crossing!! This really saved my motors' bacon yesterday, as I made the error of being the last one to cross the river and no-one waiting to tell me where to cross, or turn, once in the water. I ended up dropping into water deep enough to cover the edge of my hood for several seconds. If the air intake had been normal, I would have had one each Hydroed motor. There was enough air trapped under the hood and sheer dumb luck to let finish the crossing without incident. And yes, there were quite a few people that get to watch the crossing. Next step for me, the stealth snorkel is being completed!

When I replaced my OEM radiator on my 97, the top now rests against the radiator fill neck. There seems to be no easy way to adjust the base . (metal sleeves inserts etc.) . I took a Dremel to front edge of the top, but it did not make much of an improvement.
Any suggestions ?

Is the new rad. actually an OEM piece, or is it aftermarket? The aftermarkets seem to have a longer neck on them for some reason. You might try slotting the 2 places on top of the core support that bolts down, right where the 2 little studs come through from the rubber bumpers on top of the rad. Cut the slots forward (to the grill) just a little at a time until the radiator can tilt forward just enough to make getting the lid off the airbox and the radiator cap off easier.

The radiator is a NAPA branded Modine(?). I can get the top off will a little effort, but was concerned about the contact with the radiator neck and leading to a possible crack.

Like I said, just recut the slots. I had to with the one that I got from radiator.com.

Can I get an aftermarket intake tube with a cone filter for an 87? All of the ones I see listed are for 88+. If not what are my other options for deleting the OEM airbox?

The '87 model is the same as the rest of the RENIX stuff ( they quit the RENIX at the end of '90).