Truck Topper adds 2.1mpg at 70mph in a Gen 1 4x4 Tacoma
 

Speed/Load/MPG Tests were done on flat straight away sections of the highway. Readouts are from Ultra Gauge.

Vehicle:
1997 Toyota Tacoma 3.4L 4x4 DLX Extended Cab
http://i714.photobucket.com/albums/w...pssyg7hb2m.jpg
http://i714.photobucket.com/albums/w...ps8c2ed5c4.jpg

Testing Protocol:
A-B

Route
62.1 Miles Each Direction

Trip A (Without Topper)

20 Minutes Warmup
Ambient Temp 32f
Intake Temp 56.2
Engine Coolant Temp 192.2

Speed MPG Load RPM
45mph 30.0 28.2 1800
50mph 29.2 28.2 2000
55mph 28.5 29.8 2150
60mph 25.9 32.9 2400
65mph 24.8 34.5 2600
70mph 21.8 38.0 2900

Total trip mpg = 25.0
Trip Average Speed = 53.2mph
Total Time = 1:14

Trip B (With Topper)

Ambient Temp 41f
Intake Temp 70.4
Engine Coolant Temp 192.2

Speed MPG Load RPM
45mph 32.7 26.1 1775
50mph 32.2 26.3 1975
55mph 29.9 28.0 2075
60mph 27.3 31.4 2350
65mph 26.5 32.2 2525
70mph 23.9 35.7 2800

Total trip mpg = 27.3
Trip Average Speed = 53.7mph
Total Time = 1:12

Improvement at 70mph = 2.1mpg
Trip Improvement = 2.3mpg

9 degrees warmer could account for some of that MPG improvement. My truck gets slightly over 0.5 MPG better for 9 degrees warmer.

What type of topper? Flush fiberglass or squared off aluminum?

Flush fiberglass (pics added). I agree temps could account for some of the increase. I am planning on installing an "add a leaf" to give me more towing capacity and even out the ride height. It was pretty close before adding the weight of the topper, but the springs are really lite so it sagged about an inch when I put it on.

Nice results. Looks like a nice and smooth canopy on the truck; no window sticking out or unusual contours like mine below to cause drag.
http://i983.photobucket.com/albums/a...psdf6836f3.jpg

That's a result similar to what I see with my topper on, about 10-15%.

One of these days I'll go crazy and make a boattail topper, if the truck's use changes enough to make it worthwhile.

Nice MJ! I have been checking CL for a nice Comanche project!

Thanks! The prices of Comanches has really gone up, most likely thanks to C4C a few years ago; it's hard to find a rust-free beater for under $1k anymore. I paid only $440 in 2007 for my MJ but have done a lot of repair/maintenance work to it the past few years to bring it up to the level it is now which is a reliable DD, possible for even for a Renix rig. :)

/threadjack

I am loving your topper and hoping to have time+$ to make one like it at some point.

27.3 mpg
 

On page 70 of Adem's thesis he reports an 8.57% mpg benefit from a 'traditional' topper.
With your baseline this would work out at 27.14 mpg.This is in really close agreement with your results.
It's comforting to see these mathematical certainties come by when considering performance predictions from specific mods.:thumbup: