i experienced worse with a bed cover, kept it rolled up most of the time.

I have a Snuglid hard tonneau and saw a consistent 1.5-2 mpg increase (purely highway) when first installed (4.30s,31s,no body lift or aisins). My rear cab window also became a draw versus the vortex it was prior to the installation. Back in the day, I had several 21 - 22 mpg trips running 57-60 mph with cruise control set through an entire tank. This included (2) 180# passengers. I didn't check via GPS and who knows the % of error with the factory setup. However this was based on dividing total OD-reported miles traveled by total gallons filled.

I would expect soft-covers to make much less of a difference due to them buffeting. Brew <img src="/forums/images/graemlins/cheers.gif" alt="" />

My home made unit was a hard cover,,,

I'm actually working on a lil project to try and make the truck run on Water... Of course right now I'm experimenting on a 5 horse motor for the time being to work as many bugs out as I can before I move up to anything substantial..

Getting some rough ideas from this..

http://www.spiritofmaat.com/archive/feb2/carplans_doc.htm

Anyone have any thing else to try and add?

I found a web site a while back with a study that some grad students somewhere had conducted to test the camper shell / tonneau / tailgate up / tailgate down effects on gas mileage of pick up trucks and the gist of it was that it depends on the aerodynamics of the individual truck model. [I'd gogole it up, but I'm lazy today] Some trucks *do* benefit from those, some suffer - it just depends. I ran my truck to DC with the tailgate up (got about 21mpg) and back with it down (got about 21 mpg) - all interstate. Added a campershell and got about the same. Add some canoes and lead foot it and it suffers. As they say, YMMV...

Okay...I stuck a piece of 1/4" plywood sandwiched between the spare tire and frame and extended it to the rear bumper. It's there to eliminate a little bit of drag from the bumper. It's only a small piece fer now but I've got more mods in the works. I noticed that I should be able to button up the gap behind the rear tires to the bumper. I'm sure those gaps (approximately 36" x 12" each) can be sealed up without any problems and should take care of any bumper parachute drag. Headed on the road tomorrow (~5hr trip) and I'll see if it makes any difference... <img src="/forums/images/graemlins/smile.gif" alt="" />

While the idea is theoretically possible, there isn't enough energy in hydrogen to make up for the amount needed as input to separate the molecular bonds.