Jeep Aero mods testing - with results

[AdrianD]

Thanks for the tips and kind works guys!

Originally Posted by gumby79

Drive win it is snowing. The snow packs into stagnation points. Modifying the shape until a laminar layer develops guiding the fresh sticky snowflakes around the stagnation/impact point.
I think you will find that the snow will pack in were the road grim is . If the radius was too tight I would have expected to see recirculation / patterns like i see in the upper section


Unless you have an affinity for symmetry I would try moving both openings in the grill block to the inlet side of the radiator for better Delta T when cooling, this might also help with warmup times. You have the equipment to test. Use the scan tool and pin a land mark to the point it hits 90% thermostat open temp and first close with various startup temps. If your log will give you mi/time stamps that makes it easier.

I think your test is good enouph for a dose it work, but as stated multiple runs (3-5) avg would give a more accurate how much. Also how many mi run before testing? Cold diff oil ect. can have a large impact on results

Dream Big Chisel Down To Reality

This winter we've got almost zero snow, so no way to test using it.
I never thought about the diff oil temperature throwing me off. I just drove until the engine was up to temperature, then started testing.

Radiator tanks are top and bottom, and the inlet is at the top. Air intake is also at the top, on the right side, next to the headlight.
I will prepare some extra grille blocks to test warmup times during the skiing trip.

I had to buy a new Jeep (2 years newer than the old one) and redid the chin spoiler to reach a bit lower and have a stronger mount and changed the grille block after noticing that all new cars have the upper portion of the grill blocked off:



I also built a panel to cover a big gap in the bumper behind one of the rear tires.

On a trip to Greece this summer I had to keep my speed higher than usual, 110km/h vs 95km/h. Highway fuel consumption was good IMO given the speed and the terrain (at some point we had to make a detour through a very narrow road, up a mountain pass)
1986km, 8.157L/100km - 1241 miles, 28.83MPG

Yearly ski trip is coming up, I have a lot of fuel consumption data from my previous trips.

What next?
Maybe a bit of a horizontal extension to the chin spoiler
Blocking the rear bumper gap on the exhaust side
Full upper grill block

I will try to find some time and re-do the testing but this time measure diff and transmission temperature.

[AdrianD]

Word on the street is that swapping the transfer case from what is currently on the car (full-time 4wd, with, in theory, 100% of the torque going back to the rear wheels under normal conditions) to a part-time transfer case that allows rear wheel drive only will gain between 1 and 2L/100km.

That sounds like an insane amount. If I move fast I might be able to get the swap done before the ski trip and then have some real tank-to-tank testing.

[aardvarcus]

I have read that as well on many forums, however I have not seen any A-B numbers to support the theory. Without lockout hubs, the only real effect would be having the front driveshaft not turn, which I wouldn't attribute to that sort to MPG gain/loss. Your CVs and some parts in the diff would still spin.

I believe people believe this based on the advertised MPG of new 2WDs over 4WDs and AWDs, which typically has more to do with weight and different gears than the turning resistance of the front driveshaft.

My wife's 3rd gen T4R has the multimode transfer case (2H, AWD, 4H, N, 4L) and there is no discernible difference from 2H to AWD on friction/coasting ability.

[AdrianD]

I haven't seem real comparison tests either, so I decided not to push for a big mod before the roadtrip (a dead transfer case 600 miles from home is not fun).

Yeah, "modern" Jeeps don't have lockout hubs, so the entire front drivetrain will spin. Perhaps the people who reported MPG improvements had a messed up transfer case, ie partially locked up gerotor coupling, causing a bit of bind going down the road?

The KJ transfer case will help the plan to lift the entire drivetrain and build a slim transmission cross-member, to help clearance off-road (since I actually use it off-road). The transmission cross-member hangs down a lot, so a slim one might help aero too.

[AdrianD]

Data from the yearly ski trip, with airdam, almost complete upper grille block.
Travelling speed 60mph.

Home to regular refuelling point (~500 miles) - 27.93 MPG (8.42L/100km) - lots of traffic and windy conditions.
Refuelling point back to refuelling point (551 miles: 375 highway + back roads, the rest city-like) - 28.00 MPG(8.4L/100km)
Refuelling point to home (440 miles) - 28.33 MPG (8.3L/100km) - windy conditions again.

All in all it looks similar to the fuel consumption from this summer's trip to Greece, but at a lower speed (60 vs 65mph), the extra mod was complete blocking of the grill.
Head wind and side wind take a pretty big toll on the FE

And I finally drove through a snow storm:


Looks like I could try some smooth covers for the fog lamp pockets.

For the other purpose of the car, offroading, I turned down the wheel spacers from 1.65 to 1.38 inches, so the wheels stick out less but in order to fit larger tires, I lifted the car 0.5 inches, supposedly back to the height when it came out of the factory. The airdam is still lower than any suspension component.

In off-road trim...

[gumby79]

Very nice example of snow patching the bad spots in the nose. You can see how the snow packed in the grill slots flushing them out as the air would like to see it. Also noticed the mirrors snitching on where they want to be modified for better airflow characteristics. They say fun in the sun, takes a dark and dreary day to do this to the front end.

Dream big chisel down to reality

[AdrianD]

Looks like I would have to tackle almost everything, grille, airdam, foglight pockets *sigh*
Thanks for the observation, I was waiting for an opportunity to drive in a snow storm

[AdrianD]

Not much work done in the past two years, a newborn kid and building a house from the ground up took away my free time...


But now I have time to attempt a bit of rear aero cleanup...

This is after a 12 mile drive on a muddy road, with speeds under 30mph:


Jeep made a spoiler to help keep the rear hatch clean and people report it's helping:




Am I right thinking that if the hatch is cleaner, the rear wake is reduced, also reducing drag?

The price tag is around $150, so with 0.2L/100km gain (~2% improvement) it would pay for itself in 2-3 years at the current fuel price.

[jimhs]

I would remove the roof rack rails if I don’t use them rather than spending $

[freebeard]

Am I right thinking that if the hatch is cleaner, the rear wake is reduced, also reducing drag?

For $150 worth of Polymetal you could have coverage on three sides with a neat lap at the corners.

OTOH, the backside of the deflector has a wake.