[Big Dave]

Darcane:
Your point about wheels/tires is taken but it actually reinforces the superiority of the diesel/stick configuration. The truck has tires with a 31.7 inch outside diameter while the OD on the Impala tires is 27.0 inches. Since rotational moment of inertia goes up with the square of radius, I would expect the truck tires to have 38% higher rotational moment.

We have been over this before, but in the real world where stops lights and signs enforce stopping the higher rotational moment of inertia penalty of bigger OD tires rapidly overwhelms the lower engine RPM. With trucks the equation is always the same: Bigger tires = Lower MPG. Now that’s conventional drive trains I’m talking. It might be different with hybrids, but I notice that both Toyota and Honda put small-diameter tires on their MPG flagships.

One mitigator: The Impala has efficiency-robbing EGR where the truck does not. There is a EGR-delete kit for the LT-1, but I’ve been too busy/lazy to do it.

I hear you about the disappearing manual transmission. Let’s face it, ecomodders/hypermilers are a rare breed. The vast majority are just lazy. Talking on the cell phone is more important to most people than being aware of how you are driving. Also, I think an automatic is a way for the manufacturer tio hold the engine into a regime where NOx emissions are minimized. The very low RPM – high load regime that give optimum MPG tends to have high cylinder temps that generate a lot of NOx. Hence the rev-happy way most cars and trucks drive these days.

CFG83:
There are kits out there to convert the B-body to a Tremec T-56 (the manual available in Corvettes, Vipers, Camaros, and Mustangs). It is not a project for the faint of heart (although a cinch compared to Bennelson’s Chevedes project). Yeah, you have to cut sheetmetal. There may be such a project in this car’s future, but hopefully not this year.

As long as the gas engine has to tolerate a throttle, it will never catch the diesel for efficiency at part-load operations.