what more can I do?

[kitcar]

I've been sitting here thinking about this for the past several hours while watching Le mans. See if my reasoning is correct on this stuff. I may be over analyzing this.

I've also got a question at the end of my monologue that I'd like to discuss.

I occurred to me last night while working on the aero episode and considering what I'm going to do next (rear fender fences, btw) that I should have a fairly large level of data from my truck since I've now owned two identical trucks with different aero enhancements on them.

The old truck with the V6 (which was a Chrysler 340 with two cylinders chopped off - very inefficient) and the new truck with the V8 (4.7 liter semi Hemi, Daimler designed) the only real starting differences are that the V6 truck had slightly narrower tires (same brand, model) and had factory fender flairs. Other than that, same trans, drive shaft length, body and even rear end ratios. Same bed cover. Same grill inserts.

After looking and comparing the two databases, I noticed that using the same driving techniques with the same base starting point (grill inserts, bed cover), the starting mileage using hyper-miler techniques are almost exactly the same!

V6 - hyper @ 23.79
V8 - hyper @ 23.67

I'm not sure what this tells me other than using the same driving technique, I can get the same mileage in the same body style with two different engines (V6 EPA 14/20 V8 EPA, 13/18) with similar horsepower and way different torque.

Since I've put a front air dam, side skirts, front wheel canards on the V8 truck, I've gotten the mileage up to 26.something. So I conclude that I must be on the right track because the mileage is increasing.

I've backed this up to myself using Digimoto when I started the aero modifications. With the grill inserts and bed cover, the engine load at 65 mph was 32%. With the addition of the aero mods, the engine load is now typically 20% at the same speed and weather conditions. BTW, I can answer another question that has been bouncing around. At 65 mph with the clutch pushed in and coasting, the engine load is 0%, timing, long and short term injector timing and ignition timing are at stoplight idle values.

Another big difference I noted is kind of weird. The old truck with the V6 had one "big" difference from my current one. I had taken the spare tire off and threw it in the bed (to check it's condition) and never got around to putting it back in place. I had a 1 mpg jump from doing that. I guess having that big open space just before the rear bumper must have had some kind of diffusion effect - in the Dakota, the spare tire is full sized and is raised into position just in front of the rear bumper under the bed of the truck.

So now I have to ask myself, how much more can I do reasonably in the aero department? I've got some stuff to do the rear fences, so I'm going to do that today and drop the spare tire (just for giggles) and yeah, I can add the aeroback to the bed but I'm not sure if changing the airflow over the bed is going to gain that much - I think I'm about topped out. I don't find it discouraging; I view it much like chasing horsepower. The first 20 or 30 are easy, after that you're looking at 1 or 2 HP or even lower with tweaking.