Here's the last five tanks in the SD:

30.47
28.89
31.47
30.28
28.69

All the driving is 90% highway. Some of the trips had a/c for part of the run.

How did I get it?

A few simple things:

Speed between 62 and 70 depending on conditions. Usually 68 is preferred (by me........not by the 617.........it would prefer 55 if fuel economy was paramount).

Tire pressure at 34 psi.

Power Service...........6 oz. per 15 gallons

Allowing the speed to fall rather than mash the rack to hold speed on steep upgrades.

Boost at 13.5 psi max.

No EGR


A few more difficult things:

New valves.

2.88:1 diff.

Precise IP timing...........15°ATDC with the electronic RIV tool.


I'm quite sure that I can get additional MPG, but, at what cost? Could I ever recover the funds if I choose some exotic intake modifications? Almost assuredly, I can't.

My only additional thought is to lower the front end slightly and take advantage of a slightly improved Cd. Anything else is simply not cost-effective. This vehicle is never going to achieve 35 mpg unless I drive it at 50 mph.

And, BTW, the odometer is accurate to within .1% so you can forget any inaccuracy on that issue.............