Yaris sedan grill block testing
 

I made a crude grill block for the lower grill of my Yaris sedan. It's made of cardboard and it's purpose is for testing to see if it's worth making a nicer permanent one.

https://www.akuniverse.com/yaris_grill_block.jpg

Test:
I did 4 runs each on 2 courses, total of 8 runs. The grill block was alternately installed or removed between each run, a true A-B-A-B test. I chose high speeds so aerodynamic drag changes would be emphasized. The first course was 2.1 miles long with a slight downhill, run at 65 mph. The second course was 1.7 miles long with a slight uphill, run at 75 mph. For each run the cruise control was set at exactly the target speed and the scangauge II reset button was pressed just as the car passed a roadside marker. The scangauge II current mpg was read as the car passed the finish line roadside marker.
Conditions were cold (-5C) night time with no felt wind or traffic.
I tried my best to do everything the same for each run.

Results:
https://www.akuniverse.com/grill_block_graphs.bmp

The effect of the grill block was measurable but there was quite a bit of difference between the runs. It looks like the improvement is somewhere between 2.5 and 4.9%. That is higher than I was expecting. Also it was unexpected that the higher speed run would show less difference. I think that came from the slight uphill on course 2, as more fuel was used to overcome the hill, the difference due to aerodynamics was a smaller percent of the total. To get a more accurate number, more runs would need to be made, however the wasted gas to do this would counteract the gains made by the grill block in the first place.

If I assume a 3% fuel economy improvement over 100,000 miles, $2.50/gallon gas cost, and 43 mpg average, that comes out to $170 savings. Looks like a winner to me. I'll be making a permanent (and nicer looking) grill block soon.

Nice work, Alex.

When I did my grille block test, I saw about a 3% improvement, and at lower speeds. That said, my grille openings are inexplicably gigantic compared to your car, and closing them probably makes a larger difference.

As for the differences you saw between runs, one question I'd raise is: was the car fully warmed up for the first test?

I don't just mean coolant temp. In winter conditions, it can take the transaxle, bearings & tires quite a while to reach stable operating temps, and your mileage will also not stabilize until that point. That could explain the larger difference in the first A-B pair.

That long warm-up period is why I don't attempt much winter testing.

EDIT: Which is not to say it can't be done, just that it takes longer if you have to drive until the car is fully warm before you start testing stuff.

Very nice.

Did you cover all your openings or just the one under the license plate?

Metro is right about winter testing, I just blocked off my lower part of the grill a week ago, I did some testing but I didn't see any gains. My car seems to take almost a half hour of driving before its completely warmed up.
Also you have to be aware of your Intake air temp. If you shut off a car in the cold and let it sit a few minutes and then go drive the intake temps are way up. it takes 5to 10 miles of driving for the intake temps to even out.

You'd get better results if you blocked the upper rather than the lower grill opening, especially if your car doesn't have underbody panelling. In the absence of underbody panels under your engine compartment, all of your cooling exhaust air is going to end up under your car, adding to the drag turbulence down there. Some of the air that currently isn't entering your blocked lower grill is going to end up under your car anyway. But if you block your upper grill, all of that air is going to end up going over your car, where it creates less drag.

If you look at many sports cars (example: 1992 Camaro, and also on the 92-95 Civics), you will see that they place their grill opening very low on the front of the car just for those reasons mentioned above. On most cars, that upper grill intake is dictated by the automotive styling department, since many people don't think a car "looks right" unless it has a grill opening at the upper front of the hood. That look is a holdover from the cars of the 30's where the entire front the the car was designed around a large, tall grill.

I made mine out of Elmer's Foam Board two months ago. But it appears I should have closed the upper, not the lower, from what the above post mentions.

The pictures shows salt on the front of my Yaris Hatchback.

I only closed the lower grill because it was easier on my car, and also a little larger than the upper openings. My car does have a small underbelly, forcing all the grill air through the radiator.
I drove for about 10 minutes before starting the test so my car was not fuly warmed up. Since the runs with and without the grill block were alternating I didn't think it would matter much but maybe it did. One thing to note is the first runs on each course were the coldest and showed the best mpg (grill block was ran first).

roadrunner,
That's a nice looking grill block you made. I want mine to look like that. Your upper grill is much larger than on the sedan version.

That's a good observation, basjoos. I hadn't considered that. (Like your car, mine also only has openings in the face of the bumper. No "upper" grille.)

AlexK,
Great test and info. I'll be making a grill block tommorrow. Of course a cardboard prototype first. :thumbup:

Roadrunner,
How much did you pay for the Elmer's foam board? And, did you paint it black? What did you use to attach it as well?

Roadrunner,
How much did you pay for the Elmer's foam board? And, did you paint it black? What did you use to attach it as well?

Purchased it at WalMart a few years ago,for $2 or $3. Trimmed it to fit, then spray painted it flat black. Used black twist ties to connect it. It still looks good after a few months of driving.

I just installed a ghetto cardboard prototype grille block on the upper grille only as per basjoos's advice. Basjoos is, after all, a hypermiling sage. The weather was a perfect 64 degrees, clear and sunny, so I had no excuse not to be outside fabricating. Here's a pic...

Let us know if you see any difference in mpg! I plan on installing a upper grill block when the weather warms up. Right now it is 19 degrees outside, so no way. :(

Hey tdh1283 im just up the road in Pflugerville and you're right it was a perfect day today. Sorry peakster:( . I've mounted my upper grill blocks on several car behind the grill with great success and it not visible unless you look real hard. Just use tie wraps to hold it in place.

***to the tune of 'paint it black'
i
see
a
grill
block
and
i
want
it
painted
bla-ack

Does it look like the benefits are a combination of
1) keeping the engine warmer
and
2) aerodynamic improvement, getting that air to skip over the top of car instead

In my car ('89 Volvo 240) I can't seal up the grill because that's where my modified air intake gets it air. But I can partially block off the radiator. I'm thinking something like a plastic or aluminum screen that's maybe 80% closed, 20% open holes.

What to you people think?

hmm... with a volvo it might be better to somehow smooth off the sharp edges, but who knows it might work. there are a few good ways to find out :)

the mod is more for aerodynamics.

Yeah, I have a Dremel-type tool. Cut and grind!
Actually the 240 has rounded edges + corners. The 740 model had the sharp corners. 240 wagon has a rounded brick shape anyway, the only way to change that is with a hammer...

I have a few ideas but they will have to wait for warmer weather. Still in the 30's (F) here in CT! I think I can put some stiff plastic or aluminum on the back side of part of the grillwork; that will help the aerodynamics. Paint it black and it will be nearly invisible.

I might still put a screen over the radiator. But it has to be vibration-free so it won't kill the radiator. Maybe put it over the non-functioning ac condenser if the work access is easier.

Then I'm still thinking about some underbody panels as posted by tjts1. He did it on a 960 which has a different layout but there might still be a way to do it. For me, any project requiring laying under the car to work on it tends to get shoved to the back burner.

It's been a while, do you have any updates? I want to do this some time this spring. Did you leave the covers as is or did you freshen them up abit to match the car more?

One of the problems I have with my grill block is that around town at low speeds there isn't a lot of heat being generated by the engine because I am not burning a lot of gas but as I hit 40+mph the gas usage goes up and so does the heat. SO I was thinking that I need to automatically open the grill block more at higher speeds and it dawned on my to make a flexible grill block that bends open as the air pressure increases. If made of something that is temperature sensitive then on warmer days it could even become more flexible and open easier at a lower speed to compensate for the greater need for cooling.

I guess you could stick forced air heating vents in the grille and run a choke cable into the cabin to operate them.

Driver adjustable grill block
 

Fellow Gassavers, I believe this is the best of both worlds. A Coroplast plate sliding in a rain gutter shield (rail), operated by a choke cable.
Via Scanguage water temp, I keep the vent fully closed untill the water is up to temp. Then dependind upon OAT and vehicle speed, I know just how much to open the grill. Cheers...

https://mysite.verizon.net/tweakmenow/front.jpg

https://mysite.verizon.net/tweakmenow/closeup.jpg

https://mysite.verizon.net/tweakmenow/drivers.jpg

https://mysite.verizon.net/tweakmenow/rail.jpg

https://mysite.verizon.net/tweakmenow/cable.jpg

Yeah I was thinking of that but then thought that one time you forget and get too hot is going to be a pain. I already had some coolent leak out the water pump on a new car probably from getting a little warm bearing in mind that the cooling fans still work should they kick in at 203 degrees even with the grill blocked air gets through the radiator from between the grill and radiator when the fans run. I may go with a big cable controlled flap anyway. Blocking the bottom of the grill may get your tranny and engine oil warmer on those cold days and can help more but I usually unblock from the bottom since that block is smaller and partially open already.

Looks like you have a A/F gauge - how is that working for you?

Spring load the flap open... tape a birthday cake candle between two ends of the linkage in the engine bay somewhere... = failsafe ... when the engine bay gets hot enough to melt the candle... the flap springs open :D

JanGeo, I use the AFR gauge for a manual "lean-burn" system. Using an EFIE, I turn it off when the car needs to develop power, such as hills or accelerating onto the highway. I love it, and have the same system in my Winter Ride.

What's that?

Nate, Here is a good link:

https://www.fuelsaver-mpg.com/store/i...c0f0eb94fc35f6

In theory, You would get better fuel effiency if you had cooler air to your engine, if your coolant was cooler would that help as well?

The problem with the open grille is that it creates drag. There is still drag id you have the block as well just not as much but... What if you channeled the air? instead of having it go around the front, almost like the air would go through you...

Lubrication is designed for hot conditions so unless you can run very well controlled engine temps and lighter oil the only other solution is to keep everything warmed up ala the grill block. It does a couple of things - prevents some air from getting under the vehicle causing turbulance there and it keeps the engine and tranny warmer in colder weather. The idea is to get the air to flow around the vehicle to the sides or top also think of it as air flowing over the least amount of surface and that surface is smooth compared to the radiator and engine and underside that is very bumpy. You don't want to run cooler coolent at least not too cool or else the engine absorbs more of the combustion heat and runs less efficiently.

Deal, I see what you're talking about but a more fuel efficent engine gives better MPGs as well. Engine temp is one of the variables you should worry about.

I did a bit of research before going with a WAI. Here's what I came up with.

WAI arguments

In favor:
- Pre-heated intake mixture at low rotational speed improves combustion. (Chiu and Horng, 1992)
- Specific fuel consumption varies inversely proportional to the square root of the suction air temperature (Nakajima et al. 1969).
- Higher ambient temperature is found to increase the flame speed, the combustion reaction rate, the uniformity of the fuel-air mixture and reduce the heat transfer rate though the cylinder walls (Pulkrabek, 1997).
- For lower temperatures, only a small part of the injected fuel is vaporized, causing nonhomogeneity. As a result, lower flame speeds, higher unburned mixture, higher hydrocarbons and carbon monoxide emissions, and loss of power are observed (Pulkrabek, 1997; Heywood, 1988).


Against:
- Engine brake torque varies inversely proportional to the square root of the suction air temperature (Nakajima et al. 1969).
- Higher intake air temperature increase the occurence of engine knock (heywood 1988).
- At high engine rotational speeds, higher intake mixture temperatures decrease the volumetric efficiency of the engine (Chiu and Horng, 1992).

References:
Chiu, C.P., and Horng, R.F., 1992, ?Effects of Intake Air Temperature and
Residual Gas Concentration on Cycle-to-Cycle Combustion Variation in a
Two-Stroke Cycle S.I. Engine Equipped with an Air ? Assisted Fuel Injection
System?, JSME International Journal, Vol. 37, N.4, pp. 957-965.

Nakajima, K., Shinoda, K., and Onoda, K., 1969, ?Experiments on Effects
of Atmospheric Conditions on the Performance of an Automotive Gasoline
Engine?, SAE Transactions, SAE 690166, pp. 745-766.

Pulkrabek, W.W., 1997, ?Engineering Fundamentals of the Internal
Combustion Engine?, Prentice Hall, Inc.

Heywood, J.B., 1989, ?Internal Combustion Engine Fundamentals?,
McGraw-Hill Book Co.

Love it! Thanks for the invaluable research specs!

In favor for CAI on EFI is that you might get a little more air in than the ECU is predicting for and run a tad leaner, whereas with WAI it can go the other way, you can be too rich without further adjustment. On carbed motors, WAI wins.

However, with modest amounts of either, the difference depends on the driver. The driver without the precision calibrated right foot, will always do better with WAI because it uses less fuel per degree of throttle opening, the driver who modulates his driving technique accordingly, can use less throttle opening with CAI and save gas. Hugely overpowered vehicles with severe "tip-in" will usually always get better improvements with WAI, EFI or not. Marginally powered vehicles may work better with CAI.

These foam sheets would probably make great air dams on top of a grille
https://www.michaels.com/art/online/s...chScope=within

You could get a cool texture with this
https://www.walmart.com/catalog/produ...uct_id=7983464

Aha, I've got some of that stuff, but only in letter size, 12x18" sounds more useful, will have to check some stores to see if I can find it in that size.

I know they have really huge sheets near the Oils, that's where I "hang" out LOL