redrooster

I will try to explain this the best I can as i am not a mechanic (but am learning a lot here).

I recently went on a 4K mile road trip. While I was visiting my brother in Denver, I asked him about putting an air dam on my jeep.

I had read about how the engine bay gets air trapped up in there, which causes drag and higher coolant temps.

So - I drew out a cardboard template and my brother went to work. took him about 3 hours and he had all the tools and materials (we were lucky!).

Materials: thin aluminum powder-coated piece, long enough and high enough (the bottom edge of the air dam was 8" from the ground after it was installed); black rivets; a short aluminum L-bracket to give stability to the bottom piece so it doesn't flex in high winds; titanium bolts/nuts to fasten to the existing holes in the "spoiler"; black engine paint to paint the L-bracket; stainless steel (20-gauge) wire that was twisted to attach to the L bracket at the bottom so that the air dam would not be pushed back on the vertical plane at high speeds/winds; black heat shrink for the wire; stainless steel eyelets with locking nuts to attach wire to L-bracket.

Fortunately, the existing spoiler/air-dam on the jeep had vertical brackets underneath (I believe there were 5 of them) so that attaching the new spoiler to it would provide plenty of support, for both increased wind and weight. Black rivets were also used to attach the aluminum to the side of the wheel flairs. The sides were "rounded" by using a small fire extinguisher to roll the ends of the new dam, just enough so those end could be riveted in to the existing flairs. My brother is a race car builder and had all the tools and even had the powder-coated aluminum pieces left over from a previous racing project. Here are some pics.






The results are truly amazing. Before, I was getting about 17 mpg at highway speed. The install was done in Denver. I traveled to Santa Fe, then Austin, then San Antonio, then Phoenix, then back home to S.F. I filled up regularly and calculated my mpg. Average on the trip, going 80 mph on many of those highways, 21 mpg. My best mpg happened from Denver to Santa Fe > rolling hills a plenty. Remember those storms we had in the Midwest around the 12th of April? Thunderstorms in Texas and later, snow in Denver? Well, I was a day or two ahead of those storms, but there was a very strong north to south wind. It was my "tailwind" for that drive from Denver to Santa Fe. It literally pushed me south. MPG = 26 ! That was one time only, with about 180 miles traveled. After that, my mpg varied tremendously from around 20.5 to 23 freeway driving.

Neither my brother or myself expected such results. I kept calling him when I was on the road to report the great gas mileage. There were some other benefits as well. Normally I can feel the drag of front of the truck when there is gusty winds. Not any more. I could hear the wind at the windshield only. next, my water temp was lower, about 1/8" more to the left on the temp gauge, I guess about 10 degrees? Never got to 12 O'clock. Also, you know coming back from Arizona into the 210 at L.A., where there is that 6-mile long uphill mostly grade, before the grapevine? I've made the trip before to see my folks in Austin and always had to stay in the right lane with the trucks (drag and high altitude). This time, I could actually accelerate ! It was amazing to be able to punch it and the truck would kick into a lower gear and take off. Note: I believe that the 1989 ECU/ECM that I put into this '88 truck helped with the increased power too.

I know this sounds unbelievable, but the air dam really worked to keep the drag out of the engine bay, lower the engine temps, and consequently give me better gas mileage. Back in the bay area, I don't get on the freeway much until summer time so am getting pretty much the same 15-16 mpg around town. I want to thank Cruiser54 for his help with all the other mods and his work was an inspiration to me to get this project done.

cruiser54

Very interesting.

Bugout4x4

The physics makes sense and of course it works. I think this is not done more because of the off road clearance factor. Maybe a quick fastener removable dam maybe?

SteveMongr

Nice modification. I understand this is the sole reason for the factory air dam on a number of Jeep models, fuel efficiency.

cruiser54

I had a spring loaded one on my VW Bug.
At 35 MPH, it came down into place. Was more for keeping the front end planted at high speed than anything else. Worked well.

I've done the vertical "air dam" on a Datsun 2000 and a Datsun Z, which is not unlike what's been done on this Jeep, with excellent results in high speed handling. Never cared about fuel mileage.

Bugout4x4

That's a heck of an idea! I'm about to do something similar on my Baja Bug also. I'm going to have to use it to make a bunch trips back and forth and need to get better mileage and less wind resistance on the road. Those front fenders are currently parachutes the way they are open in the front. But I was thinking about just making one that can be quickly removed or put back with quick fasteners.

Big David

Do you really want to save fuel?

Don't run 80 mph.

investinwaffles

I mean, 80mph on the highway is pretty reasonable unless you have all the time in the world. I think going from 18 to ~25mpg is a pretty significant improvement considering the speed/drag

​​​​​​Want to save even more fuel? Walk, or push your XJ

OP, you might be able to eek a bit more efficiency by damming up the radiator a little (not completely of course)

Martlor13

it was 21mpg and went up to 23 mpg per op....once it went to around 25, but that was with lots of downhills and a strong tailwind.

s346k

vw bug...high speed...when did 5-speed commandeer your account? ive often considered a modification like this as my xj is strictly a pavement queen. end result is me not really giving af about fuel mileage. it has piqued my interest as my xj already gets 21+ mpg on the highway.

5-Speed

Haha good one! And it just so happens my air splitter is showing up today for my Bug...

TRCM

Have you checked that manually ?? IE, odometer against GPS ??

I ask, cuz I thought my 96 was getting 22 mpg or so, till I checked the speedo against GPS.

Turns out my jeep was, from the factory, off so much on the high side that after I put 31" tires on it, it is only off by 1 mph @ 60.

s346k

yes, i have checked it manually several times.

Big David

80 mph will surely get you a ticket around these parts, sonny.
I tow my XJ & guarantee you it does NOT save fuel.

Martlor13

where you from? I agree with mr waffles. 80 mph is common ground in my state. Lots of big long sections of Highway/interstate that 80 is the norm even though speed limit signs are 75...its that "token" 5 mph over the posted limit these folks reference lol