Advice on aero mods for truck (2001 Dodge Ram 2500)

[wjbell]

Originally Posted by Backtobasics

I am surprised no one has spoken of an under belly pan. There is a huge differential under the front end that catches a ton of wind.

Since it is 4wd and work based, I would look into a diamond tread or sheet metail belly pan / skid plate. I would also look at the area in front of the front wheels. Huge void, that are begging to be blocked off.
There is a lot of real estate under that truck. Skid plates would offer protection offroad, and smooth air flow.

Where is tire pressure? Many of the HD trucks have tires that can go as high as 80lbs.

It's 2WD so no front diff, but the underside does make a lot of drag I'm guessing. Tire pressure is about 70lbs.

I did a little run yesterday about 40-50 hwy miles. This was the first test I did since I took the rack off. My scangauge is calibrated pretty close I think. It usually reads 19-20 average for the hwy. Yesterday it read 24. Some of that was probably driving style changes. I'll have to wait to get back down to empty and hand calculate it to see what I actually got.

[wjbell]

Originally Posted by Backtobasics

For the record, these trans are expensive to build, and are boarderline strength wise in stock or basic rebuild configurations. I personally would not be going from drive to neutral to drive. I don't think the savings would offset the cost of rebuilding the trans... 3-4K.

Injectors (conservative) usually have better spray patterns for power and mpg.
Some lift pump manufacturers (Air Dog, FASS) claim MPG gains as a result of cleaner, water free fuel, and consistent flow to the injection pump (which is big $$).

I think you're right. 3-4K to rebuild my trans will buy a lot of fuel!

Even new stock injectors would be a major improvement. I'm sure mine with 170K probably aren't giving the cleanest spray pattern anymore.

One of the things with the FASS systems is that they remove air bubbles in the fuel to the injector pump. Stock the fuel has air in it that makes it less efficient. I don't like having to put a draw straw in though. (new tube to suck up the fuel) I actually was working on my own air bubble separator system and it worked at removing the air. (tested with a fountain pump in water then introduced air bubbles into the water) The only problem was the container I made for it leaked. I still need to come up with a good container and I think it would work.

[wjbell]

I took another 50 mile trip today up the hwy. This time I drove like I normally do, no coasting tricks. I kept it to 65mph. But before I did I had a piece of plywood, about a 4x6 sheet. So I bolted it down and used it for a sloped cover right behind the cab. But it ends 3/4 of the way before the end of the bed. My question is, does this do any good? Or is it just moving the area of drag over the top of the truck from directly behind the cab to 3/4 down the bed? The scangauge read 24.5mpg average today. So that's consistent where it always read about 20.

[t vago]

That plywood did good. You should have verification of your improved gas mileage once you fill your tank again.

[Frank Lee]

The plywood should help... BTW when GM and Ford touted "half tonneaus" they left the front half open... maybe sliding it to the rear would be even better?

[wjbell]

Originally Posted by t vago

That plywood did good. You should have verification of your improved gas mileage once you fill your tank again.

The thing is, the day before when I did a trip without the plywood the mileage read about the same.

I think I'll leave the plywood off for the rest of this tank, then put it back on for the next tank. I want to see what the benefits are without the rack first, then do the cover and see what happens then. Don't want to mix things up.

[wjbell]

Originally Posted by Frank Lee

The plywood should help... BTW when GM and Ford touted "half tonneaus" they left the front half open... maybe sliding it to the rear would be even better?

I'll look into that, maybe the main flow of air doesn't come down until partway back.

[BamZipPow]

When I experimented with a half tonneau on the back half, the numbers were higher (.5mpg on tank 1 and 1.5mpg on tank 2) than when I had just my camper top on. I only ran it this way fer about 2 tanks when I was in the start of building my aero cap. Not sure how yer side boxes will play into yer results though. Yer half tonneau should be level with yer tailgate.

[htvfd460]

Your boxes aren't all the close to your cab. Is there a way to test how much air is Goin threw there to the inside of the bed instead of around? Frank do you think that could be having play in the mix?

[htvfd460]

WJ can you get an angled photo of where the wood ends? I think it ends half way, and I could see that making a big cavity for air to circulate around in. Maybe tied with the open-ness by the cab on the sides you could try 1/2 foot increments with the wood?
My truck is running with no tailgate but it's the "Splash" bed (step side) right now. I am starting to wonder about the bed's inside width and height. So how about a sheet on the bottom of the boxes? Like a lowered T-cover. So many ideas running now. Like a little table on the bottom so you don't have to drill into your boxes. (I try to find ways firntesting so it's not a permanent change until I am good with it.) open minds can find open loops.