what more can I do?
 

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.

Well define reasonable ? I'm now thinking of a side view mirror delete myself , looks as though the ol' Stinkerbutt could benefit there also (just look at them elephant ears its got ! ) Try these at $32 including s&h kind of spendy . I recall someone posting a 'baby in view' mirror for cheap that looked very similiar .

Well, WallyWorld (Walmart) has those little cameras with lcd screed but those are $99 a pop! Delete the outside mirrors and put the screen just inside the door post.

Max, are you saying that removing the spare and opening up that bid parachute space is an increase in mpg???

Honest. See, at first back then since the old truck had virtually no power options - not even cruise control - I was on a massive weight diet on the truck, the other reason I deleted the spare. I'd doubt the loss of 40 pounds or so would increase the mileage that much so. Here's some photos of the area. With the profile of the bumper, with the spare, without the spare.

And it's really not a parachute. It's more like big arse plastic coated steel anchor. :D The bumper stands off a good inch inch from the tailgate, the license plate frame has a one inch gap at the hitch point and the upper license plate frame also has a gap. Here's photos of the deal.

In the tireraised photo, it looks like the spare really hangs down but it doesn't hang that far. The shot is from floor level. The one photo, bumpergap1 is from beneath the truck showing the gap runs the entire length of the bumper.

From what I've seen on vehicles that have diffusers built into their bumpers it looks like they dump air from under the car vertically into the wake. I've also seen some after market diffusers for the Dakota that appear to create a venturi effect under the bumper (and require the spare be relocated, oddly enough).

Not saying anything by any of this, just a curious thing I noticed. I'll take Stinker to the store later today to get more Acetone and get her up to 55 or so on the way. I know that at super cruise it will hit 27 to 29 in this weather (90 degrees, 50% humid). If it's higher we might be onto something. If not, nothing lost other than time. Crap this means I gotta put the bed cover back on. PITA. Oh well.

There are different levels of reasonable. My personal definition at this point is this:

As with the HP chase, the easier mods are also the least expensive; adding a bigger throttle body, cold air intake, IAT mods, free flowing exhaust, etc. Once you start getting into cams, heads, headers you're getting more expensive and time consuming.

With the aero chase, bolting on some vinyl for an air dam and side skirts and bolting on a bed cover - well you can do that in a few hours if you're slow. Once you get to winglets, reshaping the body and changing the physics of the wake....well now you actually have to use some formulas and engineering to get them .1 of a mpg. So is it reasonable to make 10 changes that interact together to get an one additional mpg worth the expense and effort? I dunno if I'm that type A, that's all I'm saying. Not giving up or anything just looking for the biggest bang at this point. I still have a few tricks in that bag I got from Felix that should gain some pretty good nets.

I can understand your views on that 'gain per dollar' thought . I know you use this as a work truck of sorts but minimizing the frontal profile/lowering after the other aero mods may net a decent gain as 'should' some sort of full or partial belly pan (seeing how it sees much hwy testing ) . The belly pan would be fairly inexpensive/ free.I recommend actual lowering springs to cut ones for the Dakota -which could be purchased second hand from fellow Dak enthusiasts .

Just remember "It's not the kill , but the thrill of the chase"

i would take the spair out and just make a belley pan on its place.

Man oh man, are you sure you're not like my long lost twin? I gotta call mom and ask her about that.

I actually thought about lowering the truck some time back but was able to avoid it by *tada* dropping the front air dam another inch at which point it was scraping on the ground. You'll see that in the aero episode - I have a piece of the material that I show people how to bend that was from the extension - all scraped up, sort of manly race car pocked with stones and bugs, too.

I'd like to avoid lowering at all if I can. The particular reason I have is I want to keep the suspension throw (range of travel) for "unusual" circumstances. In other words, if I need to tow 9,000 pounds for some reason, I want to be able to tow 9,000 pounds. Yes, I want my strawberry cake and have strawberry ice cream too. It's a truck. Maybe when I get that Ferrari I'll lower that.

Seriously, I really don't want to lower it. Putting the skirts and air dams on it was well as making a rear skirt for the wheel well will do the job.

And now onto the great "spare tire" delete debate that's forming on the horizon like a thunderstorm. I took the spare off this truck, threw it in the bed and it worked. Again.

Don't ask me why, I don't know. Obviously something is happening with some kind of aero effect, even with the side skirts and air dam. This is the second one of these trucks that I've owned with the exact same result. All of this is with no Acetone, which I know adds about 1 mpg at 65 mph, nothing below that. Just to really piss my bank off, I topped off the gas tank at the exact same pump after each run. I'm sure Meijer just loved me modding my truck in their parking lot.

• Spare installed, with bed cover, cruise control on. Average 24.5 mpg
• Spare installed, no bed cover, cruise control on. Average 23.5 mpg.
• Bed cover off, spare tire moved to bed, cruise control on. Average 24.2 mpg
• Bed cover on, spare moved to bed, cruise control on. Average 25.8 mpg

Go figure. Seriously, someone figure out the math on this one because I don't get it. I replicated this with two trucks with the same body, same drive train (except engines) and got the exact same results.

And here's the beauty part: I get worse mileage with the cruise. When I control the pedal in super cruise, I get better mileage. :rolleyes:

well I *do* have a 'lost' sister in the Carolinas ...not so sure about brothers any where ;)

Belly pan it .

I've noticed the anti cruise missile thing myself . Gotta be something to it .

I better get you all some video of the underside of a Dakota. Once I remove the shocks, transmission, exhaust, gas tank, spare tire, drive shaft and engine I could put a belly pan on it. I measured the wheels today once I got the spare down. 14 inches wide, 6 lugs. 6 leafs on the rear springs. 9 inch limited slip. And I get 26 mpg off this crap. What I gotta do is change the rear end and tranny to synthetic fluids, if available. I know the rear end needs friction modifiers for the center pig.

NOTHING is above the frame line. You'd either have to move everything up or hang the belly pan on coat hangers.

I'll get myself drunk and scoot under it one of these days and show you all what the underside of a real truck looks like. I think that Moose I ran over last year is still under there somewhere along with that F-150 that I ran over last month. He was out of gas at the time.

One thing I don't understand is why Dodge put the gas tank on the same side as the driver. That weight distribution doesn't make sense.