[Big Dave]

My Imp has 27” OD tires (746 revs/mile). A Crown Vic would have much the same rubber. With 3.08 gears and a 0.71 overdrive that’s roughly 1,650 RPM @ 60 MPH.

To go to 2.73 gears and a T-56’s 0.5:1 overdrive the 60 MPH engine RPM would drop to about 1,000 RPM. Doable for a L92 engine but probably beyond the capabilities of a 4.3 V-6.

L92 crate motors and T-56 transmissions are available off the shelf. I’ve considered this change. The L92 gives you a very driveable and reliable engine and mated to a T-56 where some meaningful hypermiling is possible, I could add some aero work and maybe get 25-28 MPG.

1,000 RPM operation would probably work OK for a Ecoboost V-6 but there are no crate motor Ecoboost engines unless you are well-connected.

But high-load operation at 1,000 RPM is right in the sweet spot of a Cummins B engine.

Sooner or later you have to slow down I town and the throttle starts to rip the efficiency of a gas engine. The diesel is much less affected.

BTW, chips dramatically help diesel HP and torque, but only barely help MPG. I have an outstanding MPG special chip and it gained me 0.5 MPG.

By no means could I claim to have Phil Knox’s low Cd, or even close. All I have today is a tonneau cover and a too-short air dam. Phil ruthlessly hunts down every cubic foot of air.

My truck’s superiority comes from the diesel/stick combination.