Into the weeds engine design for fuel efficiency discussion.

273 said

Really what's the OP gonna do with this?

Not saying he can't get a bit better than factory, take the 360 which is good work truck engine from 71-2002 there little difference in intown mpg throughout the years and a bit more on the highway mainly down to OD and aerodynamics and even the Hemi only had a slight improvement, with all the Chrysler and industry engineers spending billions over 30 years
basically all we got better performance with similar mileage.

Click to expand...

A friend from years ago bought a Super Bee that a previos owner had installed a 426 Hemi into. They had also installed a Corvette IRS with the stock 3.07:1 gearing. On the highway that car would get 21.3 MPG US. Suppose the trans was updated with an OD and dual throttle body sequential injection was installed. Lots of air flow with excellent fuel management. I can envision 25+ MPG.
The car still had the drum brakes on the front with the Corvette discs on the rear. Really needed the front brakes changed to discs.