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What is my trucks recommended highway speed?

Discussion in 'The Garage' started by OffRoad, Dec 13, 2006.

  1. OffRoad

    OffRoad 1/2 ton status

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    hey, i have an old chev and i was wondering how fast i can take it on the highway for long trips.

    it's a 90 c10, regular cab, long box, with 4.3 / sm465 / 10 bolt w/ 3.08s and 235/75/15 tires (29" tires)

    it didn't come with a tach for whatever reason. what is the maximum safe rpm of this truck? what does that translate to in speed?

    i only drive about 100 kph (62 mph) now. can i go faster? i don't want to ruin the motor, i can't afford another one.
     
  2. chevy wrangler

    chevy wrangler 1/2 ton status

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    on tuesday i drove my truck going about 75 for an hour and i blew a feeze plug !!LOL it took me like half an hour to replace, good thing i broke down near a checkers
     
  3. W7NB

    W7NB 1/2 ton status

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    At 2500 RPM with 29 inch tires and a 3.08 rear end you are doing 113 kph. It would depend on what RPM you consider acceptable.
     
  4. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    I used to run my 350 at just over 3000 rpm for hours at a time, and it is no worse for wear :)

    With gearing like you have, run it the full 110 km/h speed limit, and don't worry about it. Just as long as you are keeping oil pressure, thats all that matters :)
     
  5. 81jimmyslt

    81jimmyslt 1/2 ton status

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    As fast as you can, my truck gets the worst shake above 55 the hood wobbles like crazy scares the crap out of passengers.
     
  6. blazinzuk

    blazinzuk Buzzbox voodoo Premium Member GMOTM Winner

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    A 90 is considered old wow my truck must be cro magnan or something. Go as fast as you want its a modern truck. Way more modern than my 73 and I would go 75 in it when it was stock easy
     
  7. OffRoad

    OffRoad 1/2 ton status

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    i don't consider a 90 that old. i realize you guys are driving trucks from the 70s. they just rust away here. 90 is old for the rust belt.:haha:
     
  8. MaxPF

    MaxPF 1/2 ton status

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    I routinely do 80MPH (130kph) on trips, and I hold that speed for hours. I have 33's with 3.73's and a 4L60, so I only turn around 2150RPM at that speed. With the SM465(no OD) and your tires/gearing you will be turning around 2850RPM. Boats usually run 4500-5500RPM for hours on end, and your engine won't be turning anywhere near that.

    In other words, stand on it :thumb:
     
  9. OffRoad

    OffRoad 1/2 ton status

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    how do i determine my rpm at speed like you did? what's the math?
     
  10. GMCJason

    GMCJason 1/2 ton status

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    Here's the calculation for RPM:

    RPM = ((gear ratio) * (speed in mph) * (336)) / (tire diameter in inches)

    Sorry - don't have the factors for the metric version but you can convert the inputs (speed and tire size).
     

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