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Diesel's and Gearing

Discussion in 'The Garage' started by Memphis, Feb 19, 2006.

  1. Memphis

    Memphis Registered Member

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    hey guys, just looking at some M1008's with 4.56. I have been reading 4lo.com and their tire chart. Ideally, how high should a diesel be revving at highway speeds? They (4lo) are stating that 39-40" tires are ideal for 4.56 (from an economy point of view). If I wanted to run a 35" tire on an m1008 will that be revving too high for a diesel? The chart estimates that with 35" tires the revs will be sitting around 2845rpm. Will it be any different for a diesel or do I just have too much gear? :eek1:
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Having run my truck on 35's with that exact combo (6.2 and 4.56's) I can honestly say that's too much gear or not enough tire. I normally run 39.5's and even at that it's spinning at 2550 rpm. Ideal for economy? Nope...the ideal cruising rpm for a 6.2 is ~1800 at 65 mph. The 6.2 doesn't really mind the higher rpms, in fact it'll happily run at those rpms all day long...but it's pretty loud and not anywhere near as fuel efficient as it could be. 4.56 gears are awesome for a 6.2, with an overdrive.

    I'm currently rebuilding an NV4500 for my truck, and I'll run some street friendly 37's once that is in. My cruise rpm's will be 1950 rpm at 65 mph.

    Currently my highway mileage is 16.5 mpg (US gallon) and 14.5-15 mpg in town. That's 19.8 mpg (imperial gallon) and 18 mpg in town. With the 5 speed I should get into the 21 mpg range on the highway without too much trouble (25 mpg imperial gallon)

    Rene
     
  3. DieselDan

    DieselDan 1/2 ton status

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    CUCV's (w/4.56) rev to death doing any highway duty (the Army planned on a 50 mph max convoy speed :rolleyes: ).

    My '89 Jimmy with 4.56 gears and a 700R4 tranny cruised great with 35" tires (around 2000 RPM). Now with 38"s I have to drop out of OD when I hit the big hills (1800 RPMs) even with a turbo strapped to the 6.2 :waytogo:
     

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