Sorry for the long post, I type a lot.
Well, after gathering all the parts, over the weekend I finally put together an air dam on the Amocat. I used rubber hay baler/ conveyor belt, two pieces of aluminum flat bar, stainless steel nuts and bolts, and blue Loctite for assembly. Two 5/16 nuts and bolts hold the aluminum sub frame to the truck frame. I am considering this version 1.0, as it is not perfect and I can already see several tweaks that I need to make.
The conveyor belt is 7” tall, but only 4”-5” of it are hanging below the existing truck frame where I mounted it, and the remainder is blocking the front of the truck frame and the upper gap between the bumper and truck frame. The bottom of the air dam is basically at the same height as the low point on the truck, the bottom of the independent front suspension skid plate about 12”-18” behind where the air dam is mounted. The air dam is designed to stand up to abuse and being drug off-road.
Initial impressions are that it is definitely doing something, but I don’t know if it is appreciably lowering drag at this point. It is really hard to tell since I installed it right at a cold snap, and the next tank had some off-road driving on it. I did a short fill this morning just to try to get a feel for any changes in fuel economy, but my results are within measurement error. Two noticeable effects were significantly lower lift on the truck and significantly lower wind noise from the front tires. The truck definitely felt more planted in turns. I think it is also forcing more air through the radiator/engine compartment.
There are some issues with this design that I am aware of, as follows:
The very center and the two sides have some curvature, but the remaining section is very flat. It would be better if the whole thing had a gentle curve. This was a compromise I made for easy mounting, and to not interfere with the existing tow/tie down loop.
The two sides stick out to far. I built the aluminum subframe out of two 72” pieces, and didn’t want to cut them down until I had it built and installed, so the air dam ended up flush with the outer edge of the tire. Knowing the air is traveling at an angle at that point, the air dam should end before the edge of the tire. Right now, I believe I am throwing the air too far around the side of the truck.
The lower edge is flat/sharp. It would be best to have some amount of lip here to hold the air, and some amount of radius to smooth the transition point.
So here are changes I intend to apply for version 1.2 of the air dam:
Use washers or spacers towards the center to increase the slope on the two flat parts of the air dam. I am going to be limited by my tow hook, but I can get some more slant to it than what I have now. A full curve imposes mounting, tow hook, and off road issues, so that will have to wait for version 2.0.
Bend a sharper turn on the outer edges of the aluminum to tuck it up more towards the center and end the air dam sooner. This should keep the air from overshooting the tire.
Rivet some rubber hose on the bottom to create a lip and radius, while still maintaining durability and flexibility. I need to test some sample pieces first.
Reading Hucho’s book, and looking at posts on this site, I am considering making the air dam shorter in the center, and leaving it the existing height near the edges.
So give it to me straight, what are your thoughts and opinions?
In other news, I cut the windows out of my camper top, and I have sketched out some designs for a full aeroshell camper top. Once I get my air dam tuned up where I want it, I will probably begin working on this in earnest. I also got my ultragauge mounted, still need to mess with the gauges I want to appear and learn the truck’s baseline.
