Air box modification/ Filter upgrade

[child9]

Open up the inlet/lower section of the airbox so the engine isn't sucking through a smaller straw than the throttle body. Drop in a K and N air filter.

Has anyone else ever done this? I just searched and came up with nothing on , which seems odd to me. I was in my garage and noticed the air box for the 4.0L left after the engine swap. It was a great mod that netted instant results, and I was reminded of it again when my best friend and I did it to his Ducati and the affect was substantial. Easy upgrade.

 

[bluejeepkid]

I used a 1.5in unibit and drilled some holes in my airbox for extra air flow

 

[O-Gauge Steamer]

Back when I still ran a factory air box... I took vacuum measurements to see if there were any restrictions. Wound up enlarging the front inlet a bit as well as using a K&N. These days, all that is gone and I run an open element setup.

If memory serves, on the early XJs there is some sort of baffle in the tube to the TB that can be removed to improve flow.

Vacuum procedure:
1) Install a vacuum gauge connected to the intake manifold and run the engine, under load, to red line.
2) Note the vacuum reading. This is the system residual.

If the residual vacuum is less than 3"Hg, do nothing. If it is greater, then there is a flow restriction. The restriction can be found by disconnecting parts of the air delivery system, one at a time, and retaking the measurement. Once you have found the restriction, it is relatively easy to resolve the issue at hand depending on what/where it is.

In the case of my '98, the TB was the restriction...

So I replaced it. With an F&B 68mm.

Theory for a normally aspirated engine:
At WOT, the manifold should be at atmospheric pressure. What we call vacuum is a relative pressure reading, not an absolute pressure. To wit, the absolute pressure in the manifold is less than atmospheric absolute pressure so, the gauge registers "vacuum" as a method or reporting the pressure differential.

 

[lazyxj]

Open up the inlet/lower section of the airbox so the engine isn't sucking through a smaller straw than the throttle body. Drop in a K and N air filter.
Has anyone else ever done this?

Went through this a few years ago, looking for cool, un-restricted air.
I installed a temperature sensor in the air box and a ambient air sensor.
I monitor the intake manifold air temperature with a ScanGauge. I also install two ports on the air box for attaching a manometer.
My results were the stock air filter does not significantly decrease air flow. Seeing how much dirt has entered the manifolds on previous vehicles, equipped with a K&N filters, I will never use one again.
High quality paper filters work just fine and filter so much better.

Cutting out the front of the air box and then boxing the air box to channel cool air, from the grill, did not work very well at reducing the intake air temperature.
The results were much better using a cowl intake, which is what I have run for several years on my DD without any problems.
http://www.flickr.com/photos/lwade/sets/72157622703531169/

 

[child9]

Ok, cool. I figured as much. I remember putting my hand in front of the inlet and revving the engine and was amazed at how my hand was "sucked" to the hole. Once I cut the lower all I felt was air moving around my hand and not my hand being pulled, so I was happy with the progress then.

Funny thing about the TBs, too...I mean, since my latest foray into the diesel world as soon as I realized there were no TBs on them I immediately thought "that's a huge advantage right there". Every cylinder of the gas engine gets at least one of everything...except a TB. Exceptions to this are bikes and F1. Obviously this is due to cost, packaging, and maintenance concerns...but I digress. I just have always hated that, on turbo cars especially, we always have to neck the path down after the IC to connect the TB.

 

[DeftwillP]

That's some old school Dr. Dyno type stuff there.

You're not using a stock airbox with your 2jz are you?

 

[lazyxj]

One other problem of cutting out the front of the air box is that is can let in a lot water into the air box, when making stream crossings, possibly hydro-locking the engine.
I have check my XJs airbox many times after deep stream crossing or heavy rains and found no water in the airbox. As long as you do not need the space occuplied by the airbox, the cowl intake doesn't seem to have any downsides.

 

[joejeep92]

I'll prepare for the flaming but...I hate K&N and all the other brands. The oils in them no matter how carefully you oil and let dry inevitably make it to coat any sensors in your air stream. I have made a small fortune off of MAF sensors with a K&N hooked on one end. I know your Jeep doesn't have one but still. Get a good quality paper unit. As far as cutting holes I would leave it alone. In fact there is a TSB for a special plate to block off the front air inlet in water crossing situations.

 

[lazyxj]

I'll prepare for the flaming but...I hate K&N and all the other brands. The oils in them no matter how carefully you oil and let dry inevitably make it to coat any sensors in your air stream. I have made a small fortune off of MAF sensors with a K&N hooked on one end. I know your Jeep doesn't have one but still. Get a good quality paper unit. As far as cutting holes I would leave it alone. In fact there is a TSB for a special plate to block off the front air inlet in water crossing situations.

I'm with you 100% on the K&Ns. It hard to believe they still sell them. I have seen too many K&N equipped engine's intake manifolds coated with a thin layer of dirt.
I have not found a good reason why not to use a quality paper filter.

 

[cm12385]

Here comes the flaming! I first installed a K&N in my 1995 YJ when it had about 30,000 miles on it. I have ran K&N's ever since and now have 182,000 miles on the original motor, have only had to replace 1 fuel injector and O2 sensors in the 150,000 miles. I have had the intake manifold off several times over the years and never noticed a 'coating of oil' other than the normal blowback. Also my 2004 WJ and 1994 XJ (179,000 miles) have been running K&N's for some time with no issues.

 

[child9]

Cool, just a couple things:

1. I wasn't advertising K and N intentionally, I've just always used them. I'd be down for seeing empirical data that might convince me otherwise.

2. Regarding water crossings: Yeah I highly suggest if you use your rig for that you should probably go ahead and get a snorkel or some type of relocation that brings the air inlet away from the H2O. Ultimately the name of the air box game is to reduce pumping losses incurred by restricted air intake flow. How ever you do that, more power to you.

Cheers!