brian, brian, brian. you have experience with one car and one engine type. it is a turbo motor. as you will note none of the vehicles i have done have a turbo diesel motor.

so therefore your experience will naturally be different than mine.

you are entitled to conclude whatever you wish from your observations, but personally i will not begin to think that my mileage calculations will be as precise as 3% vs 7%. round numbers make a lot more sense. 20 % engine speed reduction won't equal exactly 20%. but i have found it is very close to that in my practical experience.

your personal experience doesn't equal all the physics in the world.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.