Cutting more holes in a 1998 airbox

What would happen if I cut more holes/enlarged the current hole in a 1998 XJ with a stock airbox?

You would increase the airflow at high rpm. I'd say its worth a few horsepower. The only downside is higher noise. (if you consider that a downside, I don't)

this has been done before,
From my understanding, you want 2 holes little bit smaller than the diameter of the intake pipe; maybe 2, 3"

XJ98Jeep said:

What would happen if I cut more holes/enlarged the current hole in a 1998 XJ with a stock airbox?

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It would suck more? You'd be pulling heated underhood air into the motor, how much would be deterimined by the restrictive properties of the filter you run. If you want a colder, more dense charge of air, you can modify the airbox and header opening to allow more cool air in, seal the stock opening and reverse the lid and run a tube to the cowl area for a "ram air" effect, or install a snorkel to pull air in from up high, which also has a ram effect at speed.

Many have tried all of these, some have worked better than others and are subject to opinion. Try a SEARCH..........
I've always liked the ram air idea, (first ride was built 72 ElCamino with a cowl induction hood), too bad the producers of aftermarket cowl hoods for XJ's haven't added an underhood duct for routing air to the airbox.

XJ98Jeep said:

What would happen if I cut more holes/enlarged the current hole in a 1998 XJ with a stock airbox?

Click to expand...

It works fine. I ran mine on the fender side of the airbox as that was away from the manifold. I used a standard hole saw on a drill and popped a few extra holes in. I'm not sure that the number or size make a difference since it's on the dirty side of the filter. I would think an infinite amount would be fine. :shrug:

Keep in mind that, IIRC, the later model airbox doesn't actually get its air from the grille but ambient air underhood. You might want to consider opening up the sheetmetal behind and around the left headlight and creating a flow of air there.

The early models had a hole that the airbox actually fit into that delivered cool incoming air. The later ones don't. It seems easy enough to do that.

Since I'm sitting on 33s and 6.5" of lift, I don't see water having a chance of coming in from a stream crossing. However, you might want to consider doing the cowl trick and run an air hose from the firewall and just get your air from the cowl as mentioned above. Personally, i didn't think it made that much difference and I needed the firewall space for an additional fuse block anyway.

Good luck.

Awesome, thanks guys. I'm probably going to end up opening the sheetmetal up like John90XJ suggested, so I'm off to play with power tools :yelclap:

I cut several holes with a hole saw on my street xj on the fender side also and haven't had a problem. Did the same thing on my trail xj, but used a drill bit and did several smaller holes rather than big ones. Same effect.

Go buy a 3" K&N filter, a 3" by 3" peice of PVC, and a rubber 3" to 2" pipe reducer. Install them in that order using the stock air hose out of the top of the old intake box, then yank out the stock air box and throw it in the trash. I don't know how many horses I've gained, but it runs way better than it did when it was stock and I have 31s and a fully loaded roof rack. Why cut a few more holes in the box when you can eliminate it totally run a much better air filter for about $60? Just my $.02...

...now you only have $58.98 to go... :spin1:

I knocked out the entire front wall of a bone yard 97-01 airbox, so far it breaths a wee bit better than at higher speeds, but it seems that bottom end power was a bit lower at the same time. Maybe once I get a chance to put a better muffler on it that will change:shrug: I didn't open the core support any since I live in the midwest and down want to encourage rust any more than driving it during the winter in Illinois does.