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I forgot how much fun it is on this forum!... and looking back everyone had some excellent ideas on economy. Mullet, that is what i ended up doing with the floor, but rubber-backed indoor/outdoor carpet instead of shag, and indeed that was the gist of the original flooring by the conversion company. Killingjams, I've had other people cite that exact number. That tells me that 18mpg is the glass ceiling for the 305. Not my 305, im using seals that were supposed to be replaced 100,000 miles ago. Increasing beyond 18 will likely involve either running a smaller engine and some clever gearing, or a smaller throttle body, new seals, and some clever gearing. Either way reducing power in some way other than throttle plate restriction.

The points of resistance I encounter from other people: in the case of an engine swap, a general adversion to running an engine (even a smaller one) at higher rpms, which people universally explain as "the engine has to work harder." Every engine has it's "sweet spot" and running it faster than that will decrease efficiency, but by how much? Enough to be outweighed by the fuel economy benefit of smaller displacement? In the other solution, of a smaller throttle body (the van is TBI), the AmeriV8 crowd pans the 305. If it is inferior to the 350 in every way, why is it in my van? Either way, I've never seen a larger-displacement engine get better economy than a smaller one. Ever.

Rambling. My plan is to figure out how much torque I need to keep this van moving at 70 mph, and then go to GM and other manufacturers and get this magical graph im pretty sure doesnt exist called "torque vs. fuel consumption." Pick my favorite. Which will probably be a 2-liter or something that gets my van to 70mph in 5 minutes flat.

This post is already too long, but I'd like to quickly address weight. I think it's the "white pages" from Cummins, a file online that talks about improving efficiency in tractor-trailers. On the interstate, which is my ONLY application, they say losses boil down to drag, engine inefficiencies, and rolling resistance. About 65%, 15%, 20% respectively. Weight would only affect rolling resistance, a little. Just pump up a couple more psi or something, we're talking maybe 10% of 20% here, because and only because i am not accelerating on the interstate. Stop and go in the city? All bets are off, but for the non-accelerating interstate cruise roll out the waterbeds, weight doesnt matter. Otherwise these 80,000 lb semis wouldnt be getting 10 mpg.

Grill block and front air dam will probably be it for aero mods. 70mph is my challenge, Green, I can't compromise on that! Thanks allbody!