I'm trying to put together something that can go ~50mph, weighs ~150-175lbs, and gets ~400-500mpg. After poking around a bit, I've seen that a few smaller gas engines like Honda's GX22 used on a road bicycle can result in excellent mileage (~300-350mpg) and speed (~30mph) when set up appropriately. I was thinking about putting together a diesel powered, faired, recumbent trike. Some sort of amalgamation of this http://www.wisil.recumbents.com/wisil/wianecki/leaning_trike.htm this http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=11754&item=7521626569&rd=1&ssPageName=WDVW and these http://www.velomobile.de/GB/Introduction/introduction.html would fit the bill. The only large disadvantage is increased weight, which would be ~150-175lbs. However, the diesel engine and reduced drag should offset that penalty nicely. Does anyone have any suggestions regarding where I should start and what I should be aware of when attempting to put together something like this?