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Thread: Its that time again: Better MPG for YOU

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    Senior Member SavageSun4x4's Avatar
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    Jun 2010
    17 Oaks Ranch, Boerne, Texas

    1967 to 1994

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    Default Its that time again: Better MPG for YOU

    NOTE: Pics are at the bottom of post:

    Gas prices are heading to where things are good anymore and if you own a Jeep CJ, TJ, JK make no diff, you ain't getting great mpg.

    Yea, I know there are lots of guys on the forums telling everyone how they are knocking on the door of 25 mpg or better and running a 6 in lift, 40 swampers, 6.14 gears etc.

    What can your old 4.0L really do? I rolled over 80k my old '03 Rubicon, big bumpers, winches, soft top or no top, supercharger, 4.88's and 37 MTR/KM2's and worst of all fatty weighed in at nearly 5k lbs with me, 3/4 tank fuel and fighting the trails trim

    10 - 14 mpg: Depending upon head winds, altitude, hills or flats, and how hard I push the go pedal on the highway. I run typically 60 - 65 mph, but have no problems running 75 if need be.

    If I can avoid the headwinds I can bring it in a 12-13 mpg, add 1 mpg if I can find a good trail wind/front to ride. But my best in best conditions has been 13.9

    My OEM box stock 06 LJ would see 17-19 mpg at best.

    Can you milk more out of it. Yes you can, but you may not like it. I can get low 20's and up to 24 mpg out of my'03 on the highway.

    How? Being the engineer I am and having spent a good deal of my career in R&D, I LOVE to experiment, so I do a lot of testing and some is off the this:

    Strip off the windshield, NOT folded, but OFF, strip off the sports bar, kick up the air pressure in those MTR's to about 60 lbs IIRC or the max. Now head out on a good level chunk of Interstate or in this case I 35 W heading N out of Ft Worth and drive up to the Ok state line and return ( i lived in Ft Worth) Unless you wear a full face moto helmet you will find that about 30 mph is all your face and eyeballs can stand, but I did break 24 mpg, 24.1 mpg to be exact.

    My lips nearly beat my face off, used a whole tube of ChapStik and was so windburned I thought I had washed my face in gasoline.

    Like I said, you are NOT gonna want to do this.

    As for mpg, hey you are driving a Jeep.

    A jeep has the aerodynamics of a barn door. A flat vertical surface = 1.0 CoD, Corvette Z06 is about .30/.31 Unless your Jeep is sheathed in a corvette skin you are closer to 1.0 than .30.

    Add for a big winch hanging on the front end, big tires, big non OEM bumpers, soft top, lift, trans skid etc etc. My guess: Jeep is worse than a barn door if you have all that stuff and more.

    You can drive a bit slower, you can't do much in town but on the highway 60=65 will put $ in your pocket and still get you there. Drop to 55 but do leave a lot sooner or the make up time will eat you mpg so LEAVE earlier.

    Want some extra mpg then ALWAYS use a clean air filter. I buy the cheapest ones Wal Mart sells rather than the high dollar K&N etc. I toss the low bucks at every oil change.

    Now lets get some colder air in that big air compressor (engine).

    Why cold air? Its denser so you get more slammed into the cylinder.

    "Trash Air" a Low-Buck Mod
    Getting cold air into your engine is not just important, it is critical and becomes more so if you are a rock crawler and or live in the warmer climes.

    The other day I friend of mine bought an old CJ5, one owner and ALL original. Now it is in fairly rough shape, been sitting up for way too many years, does not run, but does have a straight body and he bought it right.

    I went over to look at and noticed a very interesting item. The original air intake was hooked up to the backside of the headlight bucket. This became the genesis of this project.

    Part I:
    Couple of ways to do this:
    1)Keep your stock setup and use the trashcan to close the gap between the stock air box and the back of the headlight bucket. Also you want the bottom open to pickup the cooler air that comes under the Jeep as you drive.

    2)Toss the OEM air box and use a piece of intake tube and a cone filter into the back of the trash can
    NOTE: This is Part I and in Part II I will use the OEM air box and fit "Trash Air" to it. I chose the later since I already had a cone filter on my rig. You are going to want to put the cone filter at least partially into the trash can and get the trash can as close as you can to the headlight bucket.

    TIP: Remove the headlight trim ring to increase air flow and paint the inside around the headlight semi-gloss black to give it a dark appearance.

    Take your Dremel or a carpet knife and trim the bottom and about halfway up one side (closest to the outside) to get a good fit against your inner fender.

    Wrap the trashcan in reflective sun shade to keep radiant heat from the engine and engine bay from the filter intake. Cut your intake tube to length and join them by using a 2-inch “inside corrugated hose connector”, use the 3 2 inch hose clamps to hold the connector around the tube connection. I wrapped my tube connection with Aluminum duct tape, but any duct tape will do.

    TIP: Use scissors to cut the hose connector length-ways on one side. This will allow it to over-ride itself and give a better clamp on the tubes.

    It is all about just fitting the pieces together and doing some trimming and you have Low-Buck cold air.

    Part II:
    I converted my cone filter over to the OEM air box and I use the “Trash can” to focus the air that come from around the headlight bucket into the air box without the “OEM” horn that is on there.

    Works just as good and all the other time, materials and costs still apply.

    The real test of this will come next summer when the local temps cross the 110 F mark. This year we had 32 days of 110 and above temps.

    Is to bring cooler air into the intake and as a result run a bit better and it does.


    • Cheap plastic trash can from Wal Mart
    • Auto sun shade, reflective both sides, Wal Mart
    • Extra length of intake plastic tubing from junk yard
    • 2 inch “inside corrugated hose connector” from Home Depot
    • 3 worm drive 2 inch hose clamps
    • Home Depot 3" into 2" PVC connector


    • Dremel with “sheetrock hole” cutout drill to carve trash can or a carpet knife
    • Duct tape
    • Assorted common hand tools, screwdriver etc

    1 hours.

    About $10 bucks total.

    Worth It Factor:

    If I Had It To Do All Over Again:
    Should have done it long time ago.

    Update: I drove it for the first time after doing the fab/install and the Jeep seems to have a bit more power and response. I have a boost/vacuum gage which I drive by and it certainly appeared to have a bit more power based upon the gage on a normal trip for me.

    I have checked many time as this has provided a 1 - 1.5 mpg increase in fuel mileage depending upon how much mid range > driving I do. The big increase is in the summer.

    Now add the SavageSun PowerCone...THIS WORKS!

    Major Cold flow from grille, just like the OEM sit up on CJ

    Remove headlight trim ring to increase flow

    Wal Mart plastic trash can

    Place filter on bottom and draw circle


    Take knife or Dremel to plastic can

    OEM intake tubes to be joined

    Home Depot connector
    Check the fit

    Wrap it with duct tape

    Place trash can with windshield sun guard on can and install

    Another Home Depot, 3" in to 2" PVC connector

    Insert into OEM air box, put 3M weatherstripping on it to seal and now add cut trash can
    Last edited by SavageSun4x4; 03-12-2011 at 10:55.

    '15 Jeep Unlimited Rubicon Hard Rock...OLD SCHOOL 6 Spd Manual Trans
    17 Oaks Ranch Companies LLC


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