[racprops]

Originally Posted by slowmover

The rpm range that matters is for highway. Pulling a load. That, out of OD it is cruising at 60-mph just below peak torque is the operating environment. (Miss this and everything else goes bye-bye)

And again I am building engine that has a Low RPM range so that when I am going 80 MPH at 1600 RPMs my engine is built for it.

Lots of guys tried your way in the 1970s. Not good results.

They did not have engines built for low RPM operation so was lugging.

Take the van and get a TARE weight. Real numbers. Driver + max fuel. Then extrapolate our to axle limits. (A van is pretty much a 6,000-lb vehicle when used per design).

Same for tires. Measure the real thing as installed. Not numbers from factory brochure.
Tire rolling height is the first decision. A CRITICAL number if FE matters.

My van has a real ground effects skirts that really work.

All the ducks have to line up.

I’d investigate what rear gear ratios were available in late 1970s vans. 3.55 and 3.73 were common.

Mine is a 93 and I believe it has 343s.

Engine power comes from rpms. Not otherwise.

Many engines were built for LOW RPMs, OLDs 403, peek torque was at 2000 RPMs, the 80s Caddy 350 2200 RPMs.

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Hope that covers it.