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I've wanted to post this for a long time, but didn't want to sound like an idiot who posts something that everyone already knows.
I've decided to do so since recent new members of this board may benefit from this. I haven't seen this mentioned on this board since I first signed on.

On YJs with 4.0L HO engines (I think from 91 to 95) the reason that XJs get 190 HP and YJs get 180 HP is because there's a restricter in the airbox. It's inside the airbox cover where it meets the intake hose.
Just remove the airbox cover and pop it out with a flathead screwdriver and you'll gain a free 10% more HP.

You will feel this gain in power instantly, especially on the freeway. Now drop in an K&N and you'll have even more horses.

So if you already know this, bare with me.
Those of you who don't, enjoy the new horses.

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90 XJ traded it for
91 YJ stolen, replaced with
92 YJ
 

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Superfly
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I tried it and didn't notice a difference so I re-installed the restrictor. It's an odd place to put a restrictor, when you consider that there is a slot in it to provide a venturi effect for that small tube that intersects the air tube at the same place. By removing the restrictor, you are reducing the venturi effect and therefore the vacuum on that small tube. What effect this has, I don't know.

AFAIK, the reason there is a diff btwn the Cherokee and YJ 4.0L motors is because they use different headers.

BTW, has anyone checked to see if this restrictor is used on Cherokees as well?


...lars

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19911995409993004:144444.103512.58274



 

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i removed mine aswell a couple of months ago...seems to be running a little better but it could be "mentle".. i notice i do get a little better miledge though..

allan

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93 YJ, 4" Pro Comp Lift with 32's. Formally known as Stock Black YJ
 

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Discussion Starter · #4 ·
Hey Lars, I'm surprised that you didn't notice any difference.
I noticed the difference right the way.
How about anyone else?
Let us know if you notice any gain in power.

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90 XJ traded it for
91 YJ stolen, replaced with
92 YJ
 

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mind u i run a 2.5L...u big boys might notice a bigger differnce in power gain...

allan



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93 YJ, 4" Pro Comp Lift with 32's. Formally known as Stock Black YJ
 

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I took mine out and noticed a difference right away. I also threw away my K&N at the same time and put in a paper. K&N are great for the clean streets but only serve to force more dust into the engine on our dusty FS roads.

Lars may not have noticed a difference because he runs a slush box. I have found it is much harder to "feel" small power changes in an auto compared to a stick.

Wes

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...a member of the herd
www.hot.alloffroad.com
 

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Have heard several times about the restrictor. Seems to be a seesaw as to the effects of removing it. I haven't as of yet, but will try it over winter to see how the mileage is.

Quick side question. How interchangable are the airfilter/air boxes between the YJ and the TJ. I'm trying to play around with the air intake (located behind headlight on YJ) and fix something up with a TJ intake tube. Mind you, eventually I'll just cut a hole in the hood and run some PVC piping up there. Still figuring out the whole pop the hood and still close it with the 2 ends matching up and not screwing up the hood too much.

[This message has been edited by cdlaser (edited October 31, 2001).]
 

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I made a mini snorkle for my YJ. ABS pipe from Home Depot. Cost about $6 and it all plugged in. 2 90deg corners and a length of pipe. It now comes up and wraps around the box beside the hood. I am thinking in the future to cut a hole at the bottom of the side of the hood to extend it into a full size snorkle so I can raise and lower the hood with no interference with the pipe.

Wes

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...a member of the herd
www.hot.alloffroad.com
 

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i removed mine last year sometime and i can't really remember if i got any extra power out of it. if i did it wasn't really enough to make me jump up and down over!

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'93 sahara ~ rancho springs, SOA, EB axles, detroit, 35s, and hi steer in the works
 

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Superfly
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Originally posted by lars:
BTW, has anyone checked to see if this restrictor is used on Cherokees as well?
C'mon you Cherokee guys who I know are reading this! Have a look in the tube btwn your throttle body and air box and see if that frickin' restrictor is in there.

Thanks!

...lars

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You YJ guys are so demanding.

There is no restrictor in my 88 XJ non-HO stock air box set up. My Girlfriends 99 XJ does not have one either.

Wes, why do you say that K&N's force more dust into the engine than normal paper? My K&N gets dirtier way quicker than a paper element ever did. I assumed this is cause it is trapping more. Is there something I don't know about that you do?



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Dave
 

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Originally posted by DaveW:
You YJ guys are so demanding.

There is no restrictor in my 88 XJ non-HO stock air box set up. My Girlfriends 99 XJ does not have one either.

Thanks, Dave. I didn't want to have to be the one to tell Larry that XJ's are better than YJ's (just ask Dan)....you know how sensitive Larry can be about these things....


The '97+'s do have a crimp in the exhaust pipe as it comes down from the header though. It's meant to give clearance for the drive-shaft (as I understand it), but even with a couple inches of lift you don't need it. I've heard mixed reviews about the benefits to be had by putting an uncrimped pipe in. The degree of crimp in the pipe seems to vary from XJ to XJ - I don't think there is any measured amount of crimp to control back-pressure; they probably hired a monkey with a 5 lbs sledge somewhere along the production line; hey, at least the monkey isn't smoking a doobie at lunch on Friday such that he forgets to crimp his pipe as the line goes on by......


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DMMcG
'98 XJ
 

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Originally posted by DaveW:
Wes, why do you say that K&N's force more dust into the engine than normal paper? My K&N gets dirtier way quicker than a paper element ever did. I assumed this is cause it is trapping more. Is there something I don't know about that you do?
Yes K&N get dirtier quicker than a paper mostly because they have less surface area than paper and are sticky due to the oiling. The sticky oil quickly reaches its max dirt level though.
K&N are less restrictive thus more air and dirt get though (not to mention water). They are more a street/speed thing where the conditions are such that the air is relatively clean or the engine does not have to live very long (ie racing) or both.
I noticed right away that my air box was dirtier past the filter once the K&N went in. I do drive alot more than most wheelers in dusty conditions so I perhaps see this develop alot faster.
The biggest reason not to wheel with a K&N is they have no ability to absorb water. Unless you have a full snorkle, some drops or gallons will eventually get sucked in. The paper helps to prevent that water from getting to the engine (not saying that it will completely stop it though). K&N on the other hand just rams that water though without even slowing it down a bit.
Once you replace an engine because the filter rammed the water into it, you lose the need for that extra power.
On the other hand, when I get a "street" vehicle, it will get a K&N.

Wes

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Ok Wes, the water thing makes sense. Especially as you have first hand experience. Now, anyone out there ever tried putting the leg of a pair of panty hose over the filter (probably easier with a cone filter like myself), I have heard that this will totally eliminate water entering through the filter?

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Dave
 

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Ok Wes, the water thing makes sense. Especially as you have first hand experience. Now, anyone out there ever tried putting the leg of a pair of panty hose over the filter (probably easier with a cone filter like myself), I have heard that this will totally eliminate water entering through the filter?

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Dave
 

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Ok Wes, the water thing makes sense. Especially as you have first hand experience. Now, anyone out there ever tried putting the leg of a pair of panty hose over the filter (probably easier with a cone filter like myself), I have heard that this will totally eliminate water entering through the filter?

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Dave
 

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i have a k&n and there is no way that water or dust are getting into my engine... i guess the reason for this is i have a full snorkle and on top of the snorkle i have a pre filter that separates the dust from the air. it is a clear 'pop-corn maker' or 'lantern' looking thing that lets you see the build up of dirt that it collects. all you need to do is unscrew the top and dump out the dust/dirt every so often. this is the same pre-filter they use on 'cats' and other construction machineary that is used in dusty conditions so i know it works. plus it lets you get cold fresh air into the engine instead of hot engine air.

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'93 sahara ~ rancho springs, SOA, EB axles, detroit, 35s, and hi steer in the works
 

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Its all over Jeeps Unlimited, "remove the air restrictor and make power"
So I completely disasembly my airbox and tubes and stuff, and never found anything that was a smaller diameter than the tubing.

Maybe its an American XJ thing, cause I've never seen a restrictor on anyone I know's XJ/MJ.


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Dan
91 Cherokee, Slightly Wrinkled. 2" body lift, 3" front lift blocks, 6 non functional Super Offroader lights.
 

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i would definatly recomend this for the zj guy's,

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94 zj, platnum +4 plugs, xenon lights, 2 inch custom lift 31x10.5, k&n,
Word.
Peace Out G,
Kraqa
 
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