you need to calculate your effective gear ratio. if it actually reduces rpm 10% then the actual mileage is 22. likewise the speed will be higher so if it reads 60 the actuak would be 66.

the 81 is na so the diff would be 346.

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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.