Some A B A B A B A B A Testing results with the full undertray and no air dam.
compared to A B A B A B A B A B results with the air dam and diffuser only.
-Using Scan Gauge II trip, no fill up yet.
-Using my GPS speedometer my car is showing about 3% off (speedometer reads high) so Scan Gauge II is probably reading 3% high. Not calibrated yet
-A = ride to work 20.8 miles.
-B = ride home from work 20.8 miles. 1,400' elevation gain 1,500' elevation drop (100' net elevation drop) to work, 100' net el' gain home.
-Drives are 57- 60 mph on interstate (speed limit of 60 mph), and 45-50 mph in 45 speed limit. About 2/3 of the commute is interstate and 1/3 at 45 - 50 speed limit.
-Coast in neutral with engine on, as much as possible. About 1.5 miles of trip is 30 mph speed limit and steep.
At least 3 miles of entire trip is just coasting.
With air dam and diffuser;
To work (trip mpg)..............Home (trip mpg)
67.9 .................................64.3
71.7..................................67.7 3 mile shortened trip
66.9..................................62.2 3 mile shortened trip
68.2..................................64.2
68.3..................................69.4
With Full Undertray tied to diffuser
78.2....................................77.4 To work from gas station to work only
81.7....................................76.1
83.7....................................78.6
82.5....................................79.4
81.8....................................79.5
85.3...................................... - New all time high trip this morning
I can easily see the difference driving and coasting. I can reach 75 mpg on flat road at 60 mph and I can coast way farther now. I am getting 35 mpg on the big hills that I used to struggle to get 32 mpg on. I can now link several shorter coasts into one long coast.
I did install new front wheel bearings the same time as I installed the undertray so that does skew the data a little.