It's true that in a driving rain storm going down the highway, hardly any rain hits the bed. I've noticed that myself.
I have a theory that when a vehicle has to work extremely hard to "get out of its own way" because of having too small an engine, it runs much less efficiently. An engine with a surplus of power and good gearing can loaf along and actually potentially be much more economical (per horsepower).
For example, the too small 235 in my truck is at its very edge of its capabilities and I'm barely keeping up with highway traffic. The 1-bbl Rochester strikes me as more of an inefficient fuel dumping system rather than a precise fuel metering system.
In contrast, the huge and massively powerful 465 cubic inch big block Pontiac in my '68 Firebird gets 1 mpg BETTER gas mileage than my truck, and it doesn't even have an overdrive.
That's one point that hasn't been touched on. I feel that inadequate power in a heavy truck is half the reason these inline sixes are so horrific on gas.
