The manufacturer’s best highway mpg is 17mpg, which I could only rarely hit with tailwind in the past.
Return trip from Great Falls to Bozeman (271 miles / 11gal) saw 24.6mpg; this is 44.7% over the 17mpg best.
The trip out was a terrible headwind for 130 miles of 80mph; old mileage in similar headwind @ 80mph was 8.6mpg, this trip saw 13.8; a 60% increase.
The real number to consider is a comparison of the real actuals of mpg average improvement. Now 34 gallons for 685 miles @ 20.14mpg (Great Falls (plus 100 miles of xtra ranch trips) to SLC. Old was usually 45 gallons / 588 miles SLC to Great Falls @ 13 mpg.
The ratio of improvement from 13mpg to 20.14mpg is 55%. Two tanks of gas with an improvement of 55% proves out the third tank of gas no longer stopped for.
Let’s review the aeromods the truck gained over the winter:
The drive to Montana has “varying terrain and conditions”. 5 mountain passes of varying thousands of feet elevation gain and drop, portions of 80mph interstate, and 65 & 70mph blue highway. Conditions include wind/gale lasting hundreds of miles from singular or varied direction- so a tailwind has given the unmodified supercharged truck it’s maximum expected mileage of 17mpg on the 65-70mph sections, while it usually runs at around 15mpg in still air. A supercharged engine gives maximum performance at all times, running at a matching RPM to Speed; the only variance is how much gas it takes to maintain that speed. At 80mph mileage plummets; with a tailwind getting around 13mpg, and with a headwind 11 mpg. I was expecting an at-best improvement of around 5%, which is what adding a super-sloped aero-shell can do; essentially the shape of the Tesla Truck.
The best mileage by manufacturer is 17mpg, boosted to a best now of 20mpg: 17% gain. This means 1/3 less stops for gas, or down to two 15 gallon stops for a 19 gallon tank instead of 3 stops (vs an improbable best mileage two- fill-up trip with 16/18 gallon fill-ups with the fuel light on, sometimes for tooooo long). One less stop for gas shaves about 1/2 hour off the trip, our best time ever in the past for this route was 9 hours. This past trip, with a bit of holiday weekend traffic 100 miles in and out of Yellowstone’s west gate, was 9.5 hours, and would have been 10 hours. Along with shorter time and less fuel, is the amazing stability at speed. There is no sense of sidewind/headwind push, no semi-trailer blow-by, with exceptional in-line tracking and much lower cab noise. This is due in part to stabilizing the nose of the truck by reducing lift from the high/open Shrockworks bumber, but also due to Fluid Entrainment provided by the vortex generator AirTabs along the rear line of the shell. The amount of horsepower available is greatly increased: sailing easily over all the mountain passes, and the ability to jump to passing speed is a bit giddying. A big debate is out there on supercharged engines vs turbocharged engines, and I now I know the advantage of no turbo-lag when punching it at speed: which is also a safety issue, just at the higher end of performance. (special thanks to Julian Edgar for aerodynamic modification discussions on you-tube)
Salt Lake City to Idaho Falls with 20mph+ headwind: 210 miles at 80 mph / 15 gallons : 14mpg. Old/11 to now/14 = 27% improvement. . 400# load in bed, plus two adults, one dog, three cats. (capacity is 900#)
Idaho Falls to White Sulphur Springs: 278 miles at 65-70mph / 15.3 gallons : 18mpg. Usual Old/15 to now/18 = 20% Lighter headwind and 400# load
Return trip with 250# load, same passengers, and still air through the first half of trip, with tailwind later. Lets see: Monarch to Bozeman: 140 miles at 65-70mph / can’t give straight number as filled up in Great Falls and drove around the ranch, but it looked like 20 mpg?. nutz. can’t be right.
Bozeman, MT to McCammon, ID: 270 miles / 15gal = 18mpg. (65mph/144miles, 70mph/53miles, 80mph/74miles).Usual Old/ 15mpg to Now/18mpg = 20%. Best Old/17 to Now/18 = 5% At the end of the 65mph zone we guestimated 20mpg, and best to best mileage of 17 v 20 is 17% gain, normal to now is 15 v 20 @ 33% gain. McCammon is the farthest ever travelled on a tank of gas from Bozeman. Usually we stop in Idaho Falls <74 miles prior>, and ONCE with a strong tailwind the entire way we made it to Pocatello <51 miles past ID Falls>.
McCammon, ID to SLC, UT: 140 miles @ 80mph (mostly)/ 9 gallons : 15.5mpg with tailwind. Best Old/13mpg to Now/15.5mpg = 19% (half tank remaining, we usually get home with the fuel light just coming on, a 1/4 tank at best, or having had to fill up outside Ogden).
How does all this mpg play out at Blue Highway speeds? Best Old (17) to Avg Now (18) @ 5%. Avg Old (15) to Avg Now (18) @ 20%. Avg. Old (15) to Best Now (20) @ 33%
How does all this mpg play out on 80mph Interstate? Headwind Old (11) to Headwind Now (14.5) @ 31%. Tailwind Old (13) to Tailwind Now (15.5) @ 19%.
All decked out in her new regalia. Passenger side.
Between a few blustery snowstorms the bare metal was cleaned, etched, and given two coats of super polymer Por-15, then a spray-rubber Por-15 coating. I let this cure out for a few days, then Friday saw the center plate affixed. Saturday afternoon was the passenger unit, and today was the driver’s side and the rubber/poly airdams at the bottom for both sides.
E and I (and Nora) took it out to Saltair, traffic at 75-80mph, and there was a great improvement in handling, acceleration, and cabin noise. The bumper was meant to say “safe from deer”, but instead it hollared “off-road monster”. Now it just sings along with whatever road, or not road.
Low Center view. Each side has a lower “flexible” rubber/poly air dam for the wheel wells- held by the lower line of stainless bolts.