Jeep Aero mods testing - with results
 

Hello everyone!

With very limited time I managed to get some testing done on my Jeep. My scan tool displays and logs a ton of ECU parameters and I chose actual injection quantity and mass air flow. Instant MPG resolution is 1L/100km, which is not exactly accurate

Control test was done with this lip installed:
https://i.imgur.com/uCV86ET.jpg?1

Mod #2 was installing front tire deflectors:
https://i.imgur.com/oJ9ZefA.jpg

Mod #3 was installing a big plastic panel over the lower grille
https://i.imgur.com/64zWB6c.jpg

The test was done on the flattest stretch of road I could find, in a, luckily, free of traffic interval and I've removed from the data log entries when I was accelerating or coasting. Speed was set with cruise control to 60mph.

Control test (only lip):
Average injection quantity: 21.40 mg/stroke
Average MAF: 619.4 mg/s

Front tire deflectors:
Average injection quantity: 21.48 mg/stroke (0.37% worse)
Average MAF: 617.0 mg/s (0.38% better)

Front tire deflectors and lower grille block:
Average injection quantity: 20.89 mg/stroke (2.4% better)
Average MAF: 610.2 mg/s (1.49% better)

It's a short stretch of road, 4.5 miles total.

Just looking at the instant MPG, I was in the 6L/100km range three times with the front tire deflectors and the lower grille block, while during the other tests I was in that range only once.

Thoughts? Should I still keep the front tire deflectors?

I have the panels for blocking the upper grille ready, I just did not have time to install them today when testing.

I'd say insufficient sample. Results < 1% are down in the noise. How many passes for each of the three scenarios? Did you control for temperatures and wind speed/direction?

The deflector [apparently] leaves 2" of the tires tread exposed.

Keep it on, it looks cool.

Tell us more about the material used.

Is there anyway you can make it more of a gentle radius verses a 90 degree bend?

Testing is nice, but frankly we have a pretty good archive to know what works based on previous user experience.

If you can't reliably test fuel economy, use coast down tests. If you notice more speed at the bottom of a hill you always drive, then your mod is working. I've always found that this is noticeable in the airdams I've done.

I've also found there's a lot less noise coming up from under the floor.

The actual fuel savings are harder to measure, but if it does the above then it's got to be helping.

Please post bigger pics next time. Thanx

4.5 miles was round-trip, between 2 roundabouts. All tests done in the span of 30 minutes.

Almost 2 inches of the tire was exposed, it's less now with the new tires. Image updated in the first post.

I agree on the archive part, I've went through a lot of topics with aero mod results but nothing for a Jeep and all the trucks I could see had the wheels more tucked in.

The airdam worked, I'm sure of that, I've went through a few fuel tanks with it installed.
As for coastdown, the hills around here are all twisty or have a 30mph speed limit at the bottom :(

Heck, I even edited the current ones to comply :D

Thanks!
It's some 3 mm plastic board from a local home improvement shop. Soft surface, bendy when heated up but brittle when cold.
I've tried a soft bend on the grille block, couldn't do it, maybe I need to heat it up differently, a heat gun is too focused.

Is this a plastic laminated foam core board?

Please post a close up photo of an edge or provide a link to the material.

In my experience, chin spoilers greatly enhance stability in cross winds, and that reason alone makes them worth doing.

The results here are all only with the chin spoiler:
https://ecomodder.com/forum/showthre...l-35650-2.html

It's homogeneous in structure, I'll try to find the sticker on the board to get more info.

Looks like ABS plastic not PVC plastic, but I'm far from being sure about it.

ABS is stiffer and lighter than PVC if I recall correctly.

Plus ABS is typically black, and PVC typically white.

However, ABS is typically much stiffer and less prone to bending than fresh PVC.

It's in different colors, even yellow. Sticker not found, I will get it next time I go to the home improvement shop :)

Anyway, here is the upper grille block:
https://i.imgur.com/0T9Ed4Q.jpg

I set off to Austria for the yearly skiing holiday and used only 3 out of 5 blocking plates out of fear of overheating. When giving it the beans uphill, the water temperature went up a few degrees. Going steady uphill on the highway, no problems what-so-ever.
Running all 5 blocking plates here but it still takes about 5 miles to get up to full temperature.

Over the usual test section of highway (600 km) the trip computer showed 35.1 MPG and the calculated fuel consumption was 31.65 MPG. Exact same as the summer fuel consumption and 3 years ago when I had snow tires and just the chin spoiler. Traffic however was not the same, lots of trucks to pass, and passing on the highway in Europe means going 70-80mph. I'm pretty happy given that. Trip computer shows 28 MPG going 75mph, which is awesome.

The lower corners of the tire deflectors are now rounded off...I guess they are not stiff enough to maintain their position going 80mph.

The whole chin spoiler was wet from road spray all the way until the bend in the deflectors. Does that mean that the bend is too sharp?

On the return trip there should be less traffic.

Wouldn't leaving the middle two open provide more of a cooling benefit? Or is the point to leave those covered?

I don't know, the only discussion I've found about what openings to leave open is for an XJ which has the viscous fan and the owner openings in front of the viscous fan open for correct viscous fan operation.
My Jeep has a hydraulically operated fan, so no need for that.

Trip done, now for some numbers:
First tank, over 393 miles of highway (reference section) - 31.65 calculated MPG, 35.1 indicated MPG
Second tank, over 425 miles of highway and 120 miles of mountain roads (commute to the ski slope) - 28.2 calculated MPG
Third tank, over 457 miles of highway - 29.66 calculated MPG - strong side winds :(

Average MPG over 1396 miles - 29.586, indicated MPG: 33.128.

In L/100km, the difference between indicated to calculated consumption was 0.7L/100km for the first tank and 0.8L/100km for the trip total.

The trip from 2016 had an average MPG of 29.549. For that trip I had a stronger chin spoiler and the lower grille block.


You can see here that the chin spoiler bent back. I will modify the mounts to make it stronger and easier to install/uninstall:
https://i.imgur.com/FgjWdQu.jpg?1

Here it's obvious that there is a lot of road spray on the chin spoiler and almost nothing on the tire deflector past the bend. Should there be spray there to show attached air flow? Corner wear from tire contact is also visible:
https://i.imgur.com/jr9xUEj.jpg?1

This is how far back the deflector is pushed when going up to 85 mph, the highway was very busy and sometimes passing trucks required going that fast.
https://i.imgur.com/0wsH0oG.jpg?1

Back to the drawing board for the deflectors. I'm open to suggestions :)

Also, I'm an idiot with the grille block, I should've read this first:

https://ecomodder.com/forum/showthre...ary-13768.html

https://ecomodder.com/forum/member-f...6-bedammed.jpg

Turnbuckles.

That thing looks bad-ass :cool:

It's easier when you start with a Beetle. :)

It's not streetable, in fact they had to remove the splitter to get it on and off their trailer.

I remember reading the topic with that.

Honestly, I don't know if the car felt more stable at highway speeds because of the deflectors or because I replaced some worn control arm bushings :turtle:

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
https://ecomodder.com/forum/attachme...1&d=1576740777

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

Don't kick yourself too hard, anyone that's done the block before could have spoken up earlier on.

As for myself, I do not like grille blocks as I had an overheating issue back in 1983 when I tried my first one. There were no rules or guidelines back then, and no Internet.

Funny that #1 and #2 rules would have changed things had they been followed.

Thanks for the tips and kind works guys!

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:

https://i.imgur.com/WUOmxpH.jpg

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.

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.

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.

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.

https://i.imgur.com/VoQWj2u.jpg?1

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:
https://i.imgur.com/B2raIuo.jpg

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...
https://i.imgur.com/IWhAeyk.jpg

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

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 :)

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:
https://i.imgur.com/0CqB10i.png

Jeep made a spoiler to help keep the rear hatch clean and people report it's helping:
https://i.imgur.com/iwaQLkX.png

https://i.imgur.com/kun8bnT.png

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.

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

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.

'drag'
 

* The wing is forcing air over the roof to blow over the backlight, hopefully keeping some of the road spray from reaching the glass.
* In the past, measurements showed only drag 'increase' with such devices.
* The wing itself adds frontal area.
* And the wing has its own drag.
* To reduce drag, you'd blend a roof extension out as far as you dared, which included side extensions to box in that area, all the while providing a slight cross-sectional reduction along a streamlined path, generating pressure recovery. The only thing aerodynamics is about.
* You might take a look at the 1987 Renault Vesta-II concept, or Mercedes-Benz' Bionic Boxfish concept. The back of these two 'squarebacks' would be the gold-standard for streamlining.

Do you mean the cross bars in the 2nd and 3rd pictures? Or the longitudinal rails? I've been driving without crossbars for as long as I had this Jeep, the cross bars only go on when I need to carry things.

Understood, thank you very much for the details. I've got a spoiler off a first generation Cayenne which is fairly long, time to see how I can fit it, since I stashed it away hoping the jeep factory deflector would help.