visit with Big Dave

[aerohead]

Big Dave had business in the Ft.Worth area after the 4th of July and was able to come by late yesterday for a visit.
The heat index was high so we didn't spend a lot of time outside but we got to peruse each others pickups a little.
Dave was running his conveyor belt front airdam and color-matched A.R.E. fiberglass tonneau cover.I figure that with his robust ground clearance,that he could survive just about any Texas road kill,short of an 800-lb (363 kg)wild hog.
I got to experience his Gear Vendor Overdrive unit.I think I remember 1,035 rpm at 65 mph on I-35W.Unreal! This is something that Hucho and Gino Sovran has reported as very critical to streamlining in order to maximize mpg potential,by maintaining 'load' for BSFC purposes.
The Powermax Diesel could probably pull my house down the intestate without a blush.It's just torque on top of torque.
Anyway,we got to grab a meal in Sanger 'n toss some ideas around.
Dave got some tasty mpg numbers but I'm gonna wait 'til he's back home to report for the entire trip.He has some nice instrumentation in the cab which allows him to keep close tabs on critical powertrain parameters.Sweet!

[Big Dave]

Road trip over!

2,475 miles, mostly Interstate driving the limit (65 in Illinois; 70 in Indiana, Missouri, and Arkansas; 75 in Texas and Oklahoma) in 95+ degree weather with the A/C blasting every inch of the way.

The result was disappointing: 25.3 MPG.

I think the problem is the flat tonneau. I used to get nearly 28 with my homemade aeroshell monstrosity. (See avatar) But I couldn't see out the old black monstrosity.

I did cobble up some small mirrors that let me run with my big trailer-towing mirrors folded in. Pix coming soon as I can remember how to make my cheap camera co-operate with the computer.

I need a compromise I can see out of and still clean up the bed area.

[slowmover]

The result was disappointing: 25.3 MPG.

Yeah, but what a road trip test! Nothing to sneeze at with a 16-cpm average at 70-mph. I calc 15-cpm at 58-mph (all at $4/gl). You "earned" the shorter drive times is another way to look at it.

And anything above 95F is hard on a non-aero vehicle, IMO, as the big cooling system on these TD's start to have to work (My assigned 367 Pete starts to suffer at this point in the 95F/60% humidity days here in South Texas [which is different than North Texas]). I read that higher temps are helpful for mpg in general, but there is -- so far as I can tell -- a cut-off or trade-off that occurs at some point.

On my dead stock pickup seeing 22/23-mpg at 68-mph/1,900-rpm is a "norm" for this time of year, so your 15% plus improvement over mine is nothing to sneeze at . . you already know that if you'd kept it at no more than 65-mph that the numbers would have been even better.

Thus, I also find it useful to look at average mph over extended distances as this includes all driving plus idle time. It's then a fair way for me to trip plan and keep any (necessary) cab cooling to reasonable minimums (and a 160F interior temp is unacceptable; etc). This average, plus fuel burn is what informs me more closely no matter whether solo/empty, solo/loaded or either loaded or empty plus towing (any of a variety of trailers). Here's an example.

With a pickup truck I need to be able to understand -- predict -- my fuel burn via climate, terrain and use. Then a pickup can come into focus in the ways a car is not ever called upon to do.

Your experience with 3.08 gears has caused me to look closely at the AAM replacement 3.42 set for my stock 3.73 gears as it would, town & country, keep me closer to the sweet spot instead of always being just above it.

As to seeing out of the back, I cannot see out of my topper (glass replaced with wood and some security reinforcement), but the stock DODGE towing mirriors (down) aren't as bad as those FORD towing mirrors would appear to be. I will be trying the full replacement CIPA mirrors on mine at some future point, and am hoping they aren't the elephant ears they appear to be. SCHAFENACKER [sp?] has some that might work for you as an interim compromise. (And I liked that old idea you had of a Pontiac Trans Am rear window louver set).

Look forward to seeing and hearing more.

.

[Big Dave]

Re: "...I liked that old idea you had of a Pontiac Trans Am rear window louver set..."

Big Dave says:
That was one of the things Phil & I burned some brain cells on. Porsche and Lamborghini - cars built for top speed where aerodynamic drag is a big limiting factor) use a 'stair-step" louver for cleaning up their rear windows. Those windows are small so they cannot tolerate much blocking the vision out or the driver goes blind to the rear.

I used to have a Z-28 with those louvers, but they were of equal length and paralleled the read window.

What Phil & I discussed was a set of louvers of unequal lengths set so their rear edges described the Hucho curve. For my truck (cab top is 24 inches above the top rail of the bed and the bed is 80 inches long) to very rearmost louver trailing edge should be about 8 inches above the top of the bed rail to approximate the Hucho curve. By putting three louvers on it, I get four 4 inch "steps," but they may not be equal due to the non-linearity of the Hucho curve.

I wonder what the optimum number and spacing of "steps" would be. Bondo's gold standard aerocap essentially is an infinite number of steps with an infinitesimal spacing. That's one extreme. My flat tonneau is one step of 24 inches. That's the other extreme.

A pickup may be the hardest thing to design and test for because flexibility is the very soul of the pickup truck. The utilization scenarios are numerous to say the least. Passengers, bed load and trailers all muddy the MPG waters.

[Big Dave]

BTW, I did come up with a quick and dirty mini-mirror that allows me to fold in the dive brakes (TT mirrors).

My little Kodak camera is not computer-friendly and i don't do enough photo-processing to stay proficient at manipulating files, so it may be a while before I can post pix.

[Phantom]

Have you thought about adding farings to the back of the cab? That way you can transition the air from the back sides of the cab reducing the turbulence. It would look similar to the side view of your avatar but would not cover the back window.

Also adding a spoiler to the top of the cab might help to get a virtual angle closer to your old cover but once again keep rear view.

Here is a quick example.

[Diesel_Dave]

Originally Posted by aerohead

Big Dave had business in the Ft.Worth area after the 4th of July and was able to come by late yesterday for a visit.

I would have bought a ticket to come to that event!

[aerohead]

Originally Posted by Big Dave

Road trip over!

2,475 miles, mostly Interstate driving the limit (65 in Illinois; 70 in Indiana, Missouri, and Arkansas; 75 in Texas and Oklahoma) in 95+ degree weather with the A/C blasting every inch of the way.

The result was disappointing: 25.3 MPG.

I think the problem is the flat tonneau. I used to get nearly 28 with my homemade aeroshell monstrosity. (See avatar) But I couldn't see out the old black monstrosity.

I did cobble up some small mirrors that let me run with my big trailer-towing mirrors folded in. Pix coming soon as I can remember how to make my cheap camera co-operate with the computer.

I need a compromise I can see out of and still clean up the bed area.

I'd be encouraged by the numbers.
With the frontal area,weight,AC,winds,grades,and urban warfare she had to deal with,25.3 would embarrass plenty of passenger cars.
She'll do better.Just need that 'practical' user-friendly fix.Amazing truck!

[skyking]

Thank you Dave for the encouragement. I can fold my big towing mirrors, and always envisioned a small mirror either on the end or between the glass and the folded mirror. Time to get cracking!