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jeepgcoman 06-12-2012 11:34 AM

Aerodynamics, Anyone?
2 Attachment(s)
Since I am a never ending tinkerer, and have pretty much finished messing with the drivetrain of my WK, I am now beginning to see what can be done with the front end aerodynamics. A little background first.....a year or two ago I first installed an SRT front bumper because the difference in drag coefficient (CdA). The stock WK is .41, and it's .39 for the SRT. I don't know if it really made much difference, as I was doing engine mods at the same time. I also have Airtab ( Be sure to watch the video at the bottom) Vortex Generators installed on the WK. They only appear to work above ~40 mph and only help a little with economy (probably within the margin of error), but definitely help with vehicle stability, and especially in keeping the rear window clean. Also, removing the roof rack cross rails helps reduce drag.

I recently joined a "hypermiler" forum to gain a little knowledge on vehicle aerodynamics. Lots of interesting info. over there....they even have a cool Aerodynamics and Rolling Resistance, Power and MPG Calculator. Apparently, a little reduction in CdA goes a long way. Anyway, Since there are an abundance of problems with the WK and SRT (especially 05-07's)front end aerodynamics, I decided to do a little experiment and tape off some of the areas on the bumper, grill, and hood area to see if it made any difference. I also moved the front license plate, and it will be covered soon. Unfortunately I was only able to make one short (~200 mile) trip, and the weather (wind) conditions didn't allow for a good two way test over a known route. On the outbound leg, I usually get around 21 mpg EVIC, and on this trip I got 22.8 mpg EVIC. I know the EVIC is not always reliable but still, at this point, I was comparing apples to apples. Because of time limitations (I am off on another trip tomorrow), I decided to go ahead and do these mods. for real. When I get back I'll post pix and stats. of the results. In the mean time, here are pix of the stock SRT bumper, and the taped off, license moved front end.

Got to go out and finish it now.

4.whoa 06-12-2012 03:14 PM

Re: Aerodynamics, Anyone?
I get what you're doing,but are you gonna totally close the lower grille? Its smoother for sure, but thats alot of fresh air to block off. I've been wondering about the rear spoiler, myself.

Kayak83 06-12-2012 06:21 PM

Re: Aerodynamics, Anyone?
Subscribed to see about these air tabs...

05wkguy 06-12-2012 06:37 PM

Re: Aerodynamics, Anyone?
I like the idea,but man i would never be caught dead driving around with blue tape all over the front end of my jeep, lol

jeepgcoman 06-12-2012 08:11 PM

Re: Aerodynamics, Anyone?
2 Attachment(s)
4.whoa, all that lower SRT grill does is look good. Most of the air is deflected under the vehicle and around the suspension. See the pix below of the "almost finished product". We'll see how it works on the trip. Did you get yours running? How does the pulley work?

Kayak83, if you haven't already, check out the Airtab video to see how they are suppose to work: I've had Airtabs on my LX Hemi Magnum for about 7 years, and on the WK since shortly after I bought it. I've never noticed any great increase in economy but, as I said above, it does help stabilty and keeps the rear window cleaner, on the highway only. Around town, absolutely no difference in anything.

05WKguy, normally I wouldn't either, but it was the easiest way to do a half-a$$ed test to see if the plan had merit. I only had it on there for about a week and it certainly did generate lots of questions. I did think of using multiple colors, but didn't have any other stuff laying around.

Here's a couple pix of the semi-finished product. If it works I'll have to do a little more "cleanup" work, but what the hey.....that's what tinkering is all about. I used some cheap plexiglass, and if it works I may change it to something a little more durable.

SvenskaJeepGuy 06-13-2012 12:58 AM

Re: Aerodynamics, Anyone?
reminds me of what rutledge wood did to his challenger srt8 on top gear

4.whoa 06-13-2012 12:34 PM

Re: Aerodynamics, Anyone?
I didnt expect the plexiglass. Its there but its not :thumbsup:
Yep got her up n running, revs quicker and +.4 mpg on 2 hr test trip

bsw989 06-13-2012 08:10 PM

Re: Aerodynamics, Anyone?
.4 doesn't sound like much but could def add up over the miles!
Cool topic!

kennzz05 06-15-2012 07:06 AM

Re: Aerodynamics, Anyone?
im sorry but all i kept hearing in my head was, he must be a blast a cocktail parties

SvenskaJeepGuy 06-15-2012 05:00 PM

Re: Aerodynamics, Anyone?

Originally Posted by kennzz05 (Post 643540)
im sorry but all i kept hearing in my head was, he must be a blast a cocktail parties


jeepgcoman 06-23-2012 09:44 PM

Re: Aerodynamics, Anyone?
On Friday I got back from a 1351 mile trip to Oregon and, as promised, I'll give the results of my "aerodynamic" mods. and my observations, excuses and first assessment of the mods. First, for those familiar with Oregon, you know there are a lot of mountains, hence a lot of winding mountain driving at altitudes (in my case) from sea level to ~5500 ft. They also get a fair amount of rain and wind coming off the Pacific. All this being said, this trip was the first time, since installing my Fri Sidewinder cam that I have gotten less than 20 mpg on the highway. On this trip my overall mileage was 19.288 mpg. Now for the observations, excuses, and assessment. I'll do it with bullet statements and explanations:
--Most of Oregon has a maximum speed limit of 55 mph, unless you're on the interstate. Then it's 65 mph. My overall average speed (includes all stop signs/lights for the trip was only 41.5 mph and the moving average was only 49.7 mph.
--When I installed the cam in my Hemi, contrary to what everyone recommended, I advanced it 2 degrees, and should have advanced it 6 degrees like I did on my Hemi Magnum. My normal driving is at ~63-65 mph in 4th gear, which equates to ~2200-2300 RPM. At ~57-60 mph the RPM is below 2000 RPM, which is probably completely out of the cam's torque/hp range. If you ever do the cam mod. and live in an area with lower highway speed limits, make sure you advance the cam at least 6 degrees.
--Had headwinds/crosswinds for all but about 200-300 of the 1351 miles driven. Also, had rain most of the time driving up the Oregon coast.
--While visiting my son and grandson he wanted to show us around the Eugene/Springfield area. Of course, he had to drive...and very much enjoyed stomping on the Hemi and driving like a mad man (takes after his dad) around mountain curves. His comment...."You really have this thing dialed in." Eighty-two miles later the EVIC fuel economy went from 22.9 mpg when we arrived to 17.0 mpg when we left.
--Most of my driving around home is at ~3000 ft. altitude, and driving at or near sea level showed a very noticeable increase in power. Wish I could have taken it to the races over there.
--The so-called aero mods. I made, along with the Airtabs, did seem to help with stability in the almost continuous wind. The plexiglass covers I made for the fog light lenses and lower grill took hundreds of bug strikes, as did the windshield and the rest of the front end. In a comment by Ken Slaughter, discussing Airtab wind tunnel testing, he stated, "In test after test at the tunnel, a dirty vehicle, especially one with a bug covered windshield, would show up to a 3% hit in wind resistance at speeds above 55 MPH, which translates into a 1-2% hit in fuel economy." See the full article here:

I just finished cleaning up the mess and adding nut plates to my plexiglass mount brackets. I also cleaned up the installation a little and will do further testing.....locally, over the next few weeks. I do think these mods are worth the effort, and should help decrease the drag coefficient a little. For those who don't know, the stock 05-07 WK has a Cd of .41, and the SRT's have a Cd of .39. I'll report the results of further testing and any other changes to the current mods. Hope some other folks start messing with this stuff too. Kinda fun to tinker with it.

4.whoa 06-24-2012 11:31 PM

Re: Aerodynamics, Anyone?

Originally Posted by briando (Post 647323)
ok so i've got a silly dream. i'm looking for an aftermarket front end for my cherokee that looks like a cow catcher off a locomotive. not actually sharp and pointy but that sort of hard core get out of my way look. thought?

It wont be aerodynamic. :p

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