Question for the Aero guys
 

I have an old CJ7, most times it doesn't get driven very fast (35-40, often not more than 10) but occasionally I take it down the freeway.

I was wondering if installing a bug deflector on the hood to divert the air up over the rather vertical windshield might help.

Yer pretty much doomed by the fact that you're driving a cube down the road.

A brick has so much room for aerodynamic improvement, but I don't believe a bug deflector is one.

I agree; most of the gurus would say to work on other areas first; wheel openings, underside, maybe, and the rear.
A bugflector could work, but I have doubts about the one designed to effectively work for your jeep; those things push out a huge bubble much larger than your windshield to reduce bug splat. You would want one that's smaller or less severe, I think.

The wheel openings arent much of an option, the tires move arround too much and the tires barely clear at full travel as it is.

I am already considering a set of smooth skid plates which also get better clearance than the current one I have.

I can't really do much to the front or rear because whatever I add would just get smashed on the rocks.

I was figuring on making a deflector just big enough to get the air over the windshield.

The goal isn't to make this thing a super high FE vehicle, just to improve its road maners a bit.

first of this thing will never have good aero... it's designed to be perfect off road, and just that, so on road it will always be handicapped. So not driving it sensible and slow is your best bet...

but here's an idea that might be inspiring... it's not too extreme,cheaply doable and testable, and for the most part won't compromise the vehicles off road performance... plus i don't think it would be to noticable to other drivers if propperly done..
it's mostly for inspiration, so i went all the way, but taking parts from it that are more subtle should also help

http://i77.photobucket.com/albums/j5...y/dams/cj7.png

stock, modded, and highlighted.

main thing is an angled plate in front of the grill... this will deflect air over the grill, but basically not block it, as the sides are open, so it shoudld retain full off road cooling.

than you see that the front tires are virtually fully exposed.. what this vehicle could use is a huge airdam, so perhaps fabric or rubber "inverse mudflaps' that connect the mudguards to the bumper could be a start, than closing the bullbar (or whatever you have) and extending it as far down as possible...

if you really whant to go low you could make the lower part hinged so you could fold it up offroad.

or retain a sensible height and make the lowest part from strong rubber so that when it does hit something it will fold back....

a vehicle this aero dirty i think has the best fighting chance when the air is deflected as clean as possible around it... once that's done there's not much clean surface to keep the flow attached to and the vehicle's to short for much boattailing.

Interesting ideas there.

I'm not so sure about the grill ramp, it would still be a pretty steep angle and it would still slow the air when off road. I already have mild temperature issues as it is (even at highway speed). Ambient +120f and ambient this weekend got up to 108f. :mad: I'm going to vent the hood and see if it helps.

The air dam, were you visualizing that as vertical or slightly sloped? If its sloped I could make it solid and able to slide up on rocks.

Closing up the gap between the fender and the bumper would still be pretty steep, but should be better than a gap, and should strengthen the fender considering I'm going to remove some material above the tire to fix some mild rubbing.

Btw, that the same color as mine, but its not near as shiny, and I don't have a 4" body lift.

as for the angle of the grill block, it doesn't really matter, it could even be flat, but what is important is the corner radius at the top (if you want to optimise) if you want to streamline a brick the first thing to do is round the corners. most gains will come from the fact air is forced around the car rather than trough the messy engine and out the bottom. alternatively you could make a grillblock that's adjustable... or removable off road.

a sloped fairing would work, as with the grond clearance on your car the air that goes underneath isn't as restricted... some larger dams "mud flap" style perhaps, in front of the tires could also give an improvement at speed...

perhaps look at the lates generations of suvs and picups for inspiration on airdam heights etc

Just had an odd image pass through my mind,

Build a large fiberglass nose to put on it when going some where, shaped like a nose of course.:D with the air inlets for the radiator beig the nostrils.

Ill take a look at some of the newer SUV's (oversized station waggon's), but no guarantees, most of the new ones don't exactly scream off roadable to us.

Cj-7
 

Dr. Paul MacCready got a patent for a windshield fairing for JEEP-type vehicles.
Looking at it,you'd swear it was a parachute.The device attached to the face of the windshield framew like a 3/4 window frame with shallow tunnel inside, projecting forward as deep as the distance to the frame edge with a semicircular sweeping radius curving back around to the A-pillars,and up to the header.Looked like a rectangular fiberglass inner tube split in half.
This greater radius prevented flow separation around the otherwise squared off frame.The semicircular form prevented formation of blind spots.No one would believe that such a thing could help but I believe that something like this is one of the few things which would help you.
In a wind tunnel,at zero yaw,after painstaking work you might get the air deflected around the frame,but with any crosswind,you'd be right back with separation.
I'd look for some PVC pipe of proper size, rip it into half tube sections,miter the corners, and attach firmly.