Mirror of: http://www.concentric.net/~jman/jeepmods.html
This modification is for the 4.0 liter 6 cylinder engine in the Jeep Wrangler
(YJ). The pictures were taken of a rather muddy 1994 model, but I know
it can be done on model years '91-'95. While you're at it, you might want
to clean the throttle body. That is located at the other end of the 'hose'
(as described below). FYI, this modification will not work in a
'97 or newer Wrangler (TJ), that vehicle has a different air box. Also,
I have some information on my gas mileage before and after, you can see that below.
I've been told that this mod can be done on the '91 thru '95 2.5 liter 4 cylinder engines! I don't know if it can be done on
later years, but check out your 4 clyinder and let me know if you can do
the mod on your vehicle.
1) Open the hood and locate the air filter box. The restricter
you want to remove is inside the top piece.
2) loosen the clamp for the hose with a regular (flat end) screwdriver
3) rotate the hose to one side, you can now see the lip of the
4a) With the same regular screw driver, pry out restricter
4b) It is snug and you may want to use a second screw driver on
the opposite side to help pry it out.
5) put the hose back on the air box and squeeze shut the clamp
Your done, enjoy the extra oomph!
this is the piece that was removed.
I've been keeping track of my gas mileage since I purchased The
Jeep in July of '97. I do 80% highway, 20% city driving and I have a lead
foot. My average gas mileage up to the modification was 18.43, with a high
at 20.09 and low at 15.99. My first reading with the restricter taken off
(Originally posted 5/27/98 in rec.autos.makers.jeep+willys.
The below is posed with permission from it's author, Thomas
I have a brother-in-law who is a big wig at Chrysler and well read
whats what. This guy is a wealth of info.
He told at a party Sunday that the reason the YJ's had 10 less
horsepower that the XJ's is because there was a big to-do about
wanting the populus to be worried about safety in having too much
The decrease in HP was accomplished by putting a tapered horn inside
the air hose where it attaches to the air filter box to decrease
air flow the the engine thus decreasing HP/performance.
Sure enough, I got home, removed the hose and there it was.
that bad boy out and now I'm doing 0-60 in 5 seconds...well, maybe
that fast....kinda like being able to run faster with new tennis
guess...well you know....
(__) ( Thomas Hereford, Plymouth, MI
(oo) ( firstname.lastname@example.org
/---------\/ --< ( Product Data
( Simpson Industries, Inc.
Questions? Jason Smith