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.
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:
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.
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