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-   -   '08 Toyota 4Runner aero mods = 14% better fuel economy! (

mannydantyla 12-11-2018 05:01 PM

'08 Toyota 4Runner aero mods = 14% better fuel economy!
This is my '08 Toyota 4Runner, a 4,800 pound SUV with 4.7L V8 and all-the-time 4 wheel drive (meaning you can't put it in 2wd mode). With that information you can probably assume that it get's pretty poor fuel economy - and you'd be correct. I average around 14mpg 50/50 highway/city. Yeah that is remarkably bad. But what really shocked me was that the highway milage isn't much better than city. About 15mpg in winter and 16mpg in summer (75mpg). Very bad!

In a few weeks I'm going to drive from my home in Eastern Kansas to Portland Oregon and back, so over 4,000 miles. So I decided to do some ecomodding to the aero dynamics to see if I could improve it's highway performance.

First thing I did was delete the mud flaps, running boards, and roof rack cross bars.

For the rear mud flaps, I cut off the plastic that was extending past the body with a box cutter. I unscrewed and removed the ones in the front, then I attached them to the rear wheel openings, now they're tire spats!

Then it was time to delete the "spoiler," if you can even call it that. It's only function is to direct air onto the back window to keep it clean. Seems to me that it's a big aero drag.

It was just two bolts, some clips, and one wiring connector. I covered the holes with some gaffing tape. Gaffing tape is like duck tape that is really easy to remove and doesn't leave a residue, so like a heavy duty masking tape. It sticks really weld, holds up strong, but doesn't make a mess.

I'll have to figure out a way to get back a third brake light, for safety reasons.

Back to the front end of the vehicle, I did a partial grill block with some more gaffing tap.

I don't know if the grill block is supposed to help with aero or only help with getting the engine warmer faster, but it helps and it was easy.

[continued in next post] :turtle:

mannydantyla 12-11-2018 05:17 PM

Up until now, all the aero mods have been very easy.

But there's one very important mod that I had to make, not just for aero reasons, but for protection. It's the front skid plate - the vehicle came with one from the factory but it didn't have it when I bought it. Not only does it protect against rocks, sticks, sand, snow, etc. when off-roading, but I figure that it would also help tremendously with aerodynamics.

Here's what it looked like a few days ago:

Yeah that's a lot of dirty bits.

I could buy an aftermarket one, but I had just bought a MIG welder and a large amount of sheet metal and steel (for another project), so I figured I'd make it a project and build it myself.

First thing I did was make a scaffolding out of 1/8" steel.

Then I skinned it in 18 gauge sheet metal. This will not be thick enough to drag it along boulders, but it will protect agains sticks and snow and sand. Normal duty protection.

I make it sound easy, but it took all day Sunday to make. After the seam sealer and paint dried, I hung it up today.

There was still lot of exposed dirty bits under the truck, but I was too lazy to make more stuff out of steel. So I found a political add and got some more gaffing tape and did what I could.

[continued on next post] :turtle:

mannydantyla 12-11-2018 05:29 PM

Now for the results!

Right before starting the first mods, I did some testing to get a base score. My primary goal is to improve MPG at 75mph, so that's what I tested at.

My procedure: I live right by an interstage highway with a gas station right at the exit, so I filled up at that gas station and reset the trip meter. Drove 7 miles west, exited and turned around and drove the 7 miles back. Then I filled up at the same gas station and recorded the gas used and miles driven. I used the cruise control to keep it at exactly 75mph.

For the base score, I recorded 13.9 miles and 0.93 gallons. Which is 14.9 mpg.

Today I did it again with all the mods performed (similar weather but not exactly the same of course, but nothing else changed to the vehicle like weight or tire pressure).

I got 13.8 miles, and 0.81 gallons. That's 17mpg.

14% better!!

Yes I realize that it I should have done the test like three times for trip A and trip B but, that would have taken all day.

So for my up coming road trip to Portland, I'll be driving around 4,400 miles. Using the tool, it says I'll save $70. Which is great and all but I didn't really do these mods to save money. I hate burning more fuel than necessary and I saw an opportunity to improve something and I went for it.

kach22i 12-11-2018 09:16 PM

I'd be more than curious about the rear spoiler delete, who told you all it did was keep the rear window clean?

The gaffing tape I tried one didn't hold up to water very well (wet Michigan), lasted maybe a week on my truck. Foil tape lasted much longer but was a terrible look.

Nice work, thanks for posting.

Any plans for a full belly pan?


Spoiler Alert: Minivans and SUVs Could Become More Fuel Efficient

A specially designed rear spoiler could increase the fuel efficiency of minivans and SUVs, according to a new study detailed in Green Car Congress. The study reveals that such a spoiler could both reduce drag and nearly eliminate aerodynamic lift—effectively saving several miles per gallon worth of gas consumption. The researchers used principles of fluid dynamics and ran numerical simulations in order to craft an ideal design for a spoiler specifically designed for bluff-backed vehicles. The study was published in the International Journal of Vehicle Design, and it found "that the aerodynamic drag and lift on a mini-van moving at 108 kph (67 mph) are reduced by 5% and more than 100%, respectively, when the new spoiler is attached to it."

"Conventional spoilers resemble an inverted plane wing and generally work by increasing the downward force on the back of the vehicle as well as improving the flow of air across the bluff rear. The new rear spoiler resembles a wave in profile rather than a wing."
I'm not sure what category your rear spoiler falls under, some A/B testing may be warranted.


Spoiler Alert: Audi Patents a Sliding Wing to Improve Aerodynamics

Audi has designed this new system to improve aerodynamics on SUVs by eliminating “flow separation,” a disturbance in airflow that increases drag which usually takes place about half way down the rear window. To fight this, the movable spoiler will lower at speeds over 80 km/h (49 mph) to the right height to combat this added drag.

I was thinking at least a clean sharp edge for the air to release from is a consideration, similar to the below.

Bizon Truck Cab Spoiler

It's a snap to add a spoiler to your truck. Bizon designed their cab spoiler to install without any cutting or drilling. it has pre-applied 3M automotive tape, the same stuff that holds on a lot of the factory trim & badging. All you need to do is make sure the area is cleaned well with rubbing alcohol, peel, and stick.


matt36415 12-16-2018 07:24 AM

Is there a reason not to slow down to 60? Surely that would be the simplest and by far most effective way to reduce fuel use.

Out of interest, what are the speed limits there? In Aus the highest is 110kmh or about 67mph except some roads in the Northern Territory where pretty much no one lives.

slowmover 12-16-2018 03:46 PM


Originally Posted by matt36415 (Post 586197)
Is there a reason not to slow down to 60? Surely that would be the simplest and by far most effective way to reduce fuel use.

Out of interest, what are the speed limits there? In Aus the highest is 110kmh or about 67mph except some roads in the Northern Territory where pretty much no one lives.

The stupidity of todayís drivers cannot be overstated. Safety, vehicle longevity & reliability are out the window. FE doesnít matter either.

Following too closely is the worst (attended by the belief itís is legal to travel in the passing lane; it isnít) as under 300í space isnít cause for concern (it should be) and at 50í many will travel for miles. Hell, days.

NEVER EVER allow oneís self to be surrounded by other vehicles is the key. Ever heard the phrase, ďcanít fix stupidĒ? Thatís the guy inside any crowd. For any length of time.

When the morons are trying to form up, cancel cruise and drift down about 10-mph. Itís NEVER safe to have others around. Itís reason to hit the brakes.

Firearms and drunk teenagers. Thatís the EXACT risk analogy for trying to run at the upper limit. As nothing else in life has such life-changing consequences. An obese, alcoholic, chain-smoking desk dweeb will outlive the fools with firearms and bad driving.

Remember that at your funeral someone will tell the obese, alcoholic, chain-smoking desk dweeb that we are glad heís not as stupid as was the guy we are burying.

Traffic volume determines top travel speed. Which is almost never the actual limit.

That covers risk reduction. Spacing determines set speed, and is dependent on traffic volume. Always more than 300í. At 700í, relax.

Fuel economy is in steady-state cruise. Engage cruise control on the entrance ramp. Cancel it to drop off in speed when the fools gather around one (10-mph). Re-engage on a downslope where convenient. Itís always turned on and in use until the end (except the few times when cancellation is best).

With no acceleration or braking events, and maybe passing two-three vehicles on a 600-mile or 12-hr day (the maximum daily distance) the choice of travel speed will be likely be near 65-mph or a little lower.

The needed information is in average mph. The actual time of the trip. From engine start to car parked at dayís end. Total miles divided by time. It wonít be anywhere near travel set speed.

Thus the real trick to high average mph is

1). Location, number and length of stops.

2). Time of departure.

Letís do last first. Nationwide, traffic is lowest from 2300 to 1100. So start early. I start at around 0300. A good day for me in the Peterbilt is to have 500-miles done before noon. That happens only if everything goes well.

Planned stops. Always do this the night before. Zero unplanned stops. Itís every two hours or roughly 100-miles. A quick exit to the restroom is fine if some walking is involved.

Every four hours is a one hour break. Let this coincide with the fuel stop and/or meals.

The successful day is in knocking out those two-hour or 100-mile legs. What comes before or after is irrelevant. Skill in vehicle-handling is dependent on alertness. Fine motor skills. Without breaks as above (scientific study) those skills fall away. (Which is also accident avoidance).

Make the plan. Use Exit numbers. Stop point in the same direction of travel. No crossing major metro areas late in day. Etc.

These breaks arenít optional. Theyíre built-in to the successful plan.

Again, average mph: the higher the travel set speed, the greater will be the divergence between travel set speed and average speed. And the worse the economy. (Itís not all aero problems; itís in compounding them).

And that steering wheel corrections per 100-miles traveled is a valid FE marker, obviously lane-changing works against one. The more so in having to brake or accelerate to maintain constant speed.

I get drivers all the time on the CB complaining about slow trucks in their way. It shuts them up EVERY TIME when theyíre reminded their trip plan failed. Didnít leave early enough, either. You drive big trucks for a living and this becomes apparent right away. Every vehicle out there is constrained by safety (except in the pea brains of todayís car drivers; it was never this way until under twenty years ago).

A 4,000-mile trip is barely over a week for me. I average above 10,000-miles per month. Hit 120k for the calendar year last week. Habits and preparation are everything. Ronnie Reagan was in the White House last time I had a traffic ticket.

The miles around oneís metro area donít count towards anything. Itís all familiar. False bravado ensues on cross-country trips. There are differences from every geographical locale and state.

Whatís the real difference between running 62 or 72? The latter seems enjoyable because 90% of Americans report it as fully engaging. Any faster and the peripheral cone of vision narrows too far.

In other words, itís work.

At 62 one arrives relaxed. Thereís been no fight. Oneís peripheral vision includes the scenery. Itís what vacationing is about. At either speed itís still the rhythm of from one set point to another.

Whatís the time difference? Maybe the spread from 55 to 63-mph ON AVERAGE.

In other words, not worth the trouble to stay with the racing morons all day. I sincerely assure you thatís what they are. ******* children who never had parents. No baby daddy cared enough. Iím happy to tell father & son this, to their faces. Neither is father OR son.

The relation of guns to cars is that it only takes ONCE.

Talk of skill is a laughing matter. And irrelevant.


grins2go_brett 12-17-2018 01:07 PM


Originally Posted by mannydantyla (Post 585702)
I covered the holes with some gaffing tape. Gaffing tape is like duck tape that is really easy to remove and doesn't leave a residue, so like a heavy duty masking tape. It sticks really weld, holds up strong, but doesn't make a mess.

Just a note on gaffing tape. I'm a professional Photographer and I use gaffing tape all the time to tape down cords at events. I've also used it on my van for various mods, experiments, and temporary fixes. In the winter time, you will probably be ok with it not leaving too much of a mess. But leaving it on in higher temps and direct sunlight for long periods of time, the adhesive will degrade and leave a mess on the vehicle. I speak from experience. Lots of Goo Gone or Goof Off and elbow grease experience. ;):)

Also, keep it up and do what you feel is right for you! I know you've received some pretty strong comments and opinions here. But do what you can with what you have available and make it work. :)

mpg_numbers_guy 12-17-2018 01:12 PM

Coroplast and zip ties work well. Rustoleum flat black paint works quite well and sticks to the coroplast. Or duct-tape covered cardboard painted black or use black duct tape. Worked well and handles the weather fine. Plus, as grins2go_brett said, you avoid dealing with residue issues from the tape on your car. Just a thought. :)

kach22i 12-18-2018 10:32 AM


Originally Posted by grins2go_brett (Post 586282)
Just a note on gaffing tape..............

I believe there is a great disparity in precipitation between respective our climates.

Michigan is a whole lot wetter than Arizona.

On the other side of the coin, gaffing tape in Michigan isn't going to have the UV degradation issues of Arizona.

I'm going to guess that Lawrence, Kansas is somewhere in between.

mannydantyla 12-19-2018 12:43 PM

Thanks guys!

Yeah the gaffing tape will certainly see a lot of weather between Kansas and Portland. And it will be getting us around the Portland area for 4 or 5 days, and Portland got 3" of rain in 24 hours a few days ago. I'll keep a roll of duct tape with me just in case.

The reason why I measured at 75mph and not 60mph is because 75mph is the interstate speed limit in most states these days, and that will be the speed I will go. We're making it a 3 day trip, but even then those will be long long days. Slowing down to save on fuel will not be an option. But this is not a fast speed, these days, and I'm always passed by all the other drivers except the big rigs. Even at the speed limit, I seem to be the slowest car on the road.

But for much of the drive, other vehicle on the road won't really be a factor. There will be a lot of lone, lonesome stretches, especially in Kansas, Wyoming, Idaho, Utah, and East Oregon. I hear that I-80 will be mostly truckers (just what I've read, I've never been on that road). I-70 between Denver and the ski resorts will be insane, but I should hit that stretch on Saturday afternoon, well after the crazies have all raced to the slopes. I'm thinking about taking US-50 through Colorado on the way back but I'm not sure yet.

As per the comments about the "******* children who never had parents," that was quite a rant. Do you feel better now?

When my wife is driving, she'll likely go even faster. She drives about 90 on average on her daily commute to work. I'm always telling her to slow down but she has "small car syndrome" as I call it (Toyota Yaris). She hates when another car passes her, especially if it's a SUV or truck, she feels like it's a personal threat against her because her car is small. So she "defends" herself against the bigger vehicles by driving past them as quick as possible.

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