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RPM's for a Detroit S60/10/2.64

Hi all,

Can anyone offer any advice on how to get the best mileage out of a Detroit with a 10 speed and 2.64 rears? (not my first choice, but I can't afford to swap at this point).

I find if I let my RPMs get up too high, all I hear is the turbo and watch my mileage decrease, however, if I keep the RPMs in the 1200-1300 range, the slightest whiff of a hill means I have to bury the pedal and/or shift, which.. there goes the mileage.

Any advice is appreciated!

-- Victor

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Based on where I haul and what I haul (rolling hills average 35K in the box), I find 1400-1475 (61-64 mph) does pretty good for me. I am running 18 speed with 2.64 and primarily use 16th direct at cruise. On lighter loads, flatter ground, I find 1325-1375 (58-60 mph) does pretty good for mpg. Truck has averaged 7.93 lifetime. I stay up north all year round. On hard, long pulls, 1500-1525 is better for keeping EGT's down. I have ceramic exhaust manifold and Borg Warner 171702 turbo with a blanket on it. Been real windy lately, so mpg's have taken a hit. Did pop a 10.4 mpg for a trip recently. Had a 10 mpg offset tail wind and about 15K in the box running at about 1375 RPM. Detroit 60's are not low RPM engines like the newer engines. Unless you are on totally flat ground and wind is favorable, do not run it like the new engines. They do real well for most things in the 1400 range. And they like a smooth, streamlined exhaust setup. Else EGT's climb and stay up high because of low exhaust flow and cooling after the turbo that creates some back pressure. It is fighting with itself at that point.

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Thanks! I am trying to retrain my ear to not want to run around 1100-1225, as this doesn't suit the engine at all. I'm finding that 1400 isn't a bad cruising RPM, but that I have to watch how and work hard at how I get there. Obviously, I'd love to have a 13/18 over this 10 speed, but for now it is what it is.

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