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Easy engine RPM calculator

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by marine_enlisted, Apr 15, 2004.

  1. marine_enlisted

    marine_enlisted 1/2 ton status

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    I found this while surfing. I'm sure many of you have seen it, but some may find it very useful...I did. Plug in your tire size, gear ratio, tranny type and MPH, and it tells you your engine RPM. /forums/images/graemlins/thumb.gif
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    [ QUOTE ]
    I found this while surfing. I'm sure many of you have seen it, but some may find it very useful...I did. Plug in your tire size, gear ratio, tranny type and MPH, and it tells you your engine RPM. /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    You forgot the link...or was this the psychic calculator? /forums/images/graemlins/grin.gif

    Rene
     
  3. marine_enlisted

    marine_enlisted 1/2 ton status

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  4. Muddytazz

    Muddytazz 1 ton status

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    That calculator tells me that with my 33's and 4.10's and 55mph I'm running 2357 rpm's and I know that is WAY off, its more like 2900rpm's
     
  5. TxK5Blazer

    TxK5Blazer 1/2 ton status

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    I agree with muddytazz it is off oh well ...Jason
     
  6. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    55 mph, 4.10's and 33's with a non lock-up automatic would be 2425 rpm at 55 mph. Time to get a better tach...

    mph x final drive ratio x 355 (for non lock-auto) / tire diameter.

    55 x 4.10 x 355 / 33= 2425 rpm

    with a lock-up tranny or a manual tranny you'd use 336 instead of 355.

    Rene
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    [ QUOTE ]
    I agree with muddytazz it is off oh well ...Jason

    [/ QUOTE ]

    It's right on the money...at least for a manual tranny without OD.

    Rene
     
  8. Muddytazz

    Muddytazz 1 ton status

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    Come down and drive my burb, with the TH350 and fulltime 203 its running HIGH rpm's....you can tell its higher than 2500 rpm's
     
  9. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Are you claiming your ear is more accurate than math or a proper tach? /forums/images/graemlins/thinking.gif

    Rene
     
  10. Muddytazz

    Muddytazz 1 ton status

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    I'm not arguing with ya Rene, but with a damn near brand new tach that at 55mph, it definitely sounds like it needs to shift again because of the high sounding rpm's.
     
  11. marine_enlisted

    marine_enlisted 1/2 ton status

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    I'm sure there are gonna be a few variables that this thing won't compensate for. As you know tire hieghts vary greatly due to wheel width, wear, and manufacturers rounding to the nearest larger size. Also, the final drive ratio is not going to be the same for every vehicle.
     
  12. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I check my tach using the math, not the other way around. I drove for 4 years with only a tach and no speedo. Using the math I could tell you with 3-4 mph of my true speed. I went through quite a few speed traps without ever getting nailed. In Oregon of all places I've seen the un-manned radar trailers and my speed versus rpm was always very very close to the math. The math works...unless your tranny is slipping badly.

    For true tire diameter measure the circumference and divide by pi.

    At 2500 rpm or so it should sound like it needs to shift again.

    Rene
     
  13. Derf00

    Derf00 1/2 ton status

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  14. TopOff

    TopOff 1/2 ton status

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  15. jjlaughner

    jjlaughner 3/4 ton status

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    [ QUOTE ]
    Here is the best one I have ever seen:

    Florida 4x4

    [/ QUOTE ]

    /forums/images/graemlins/waytogo.gif /forums/images/graemlins/peace.gif
     
  16. RingMaster4x4

    RingMaster4x4 1/2 ton status Premium Member

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    [ QUOTE ]
    Here is the best one I have ever seen:

    Florida 4x4

    [/ QUOTE ]


    If that one I right I normaly going about 80 down the high way. /forums/images/graemlins/yikes.gif /forums/images/graemlins/doah.gif /forums/images/graemlins/whistling.gif
     
  17. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    [ QUOTE ]
    I found this while surfing. I'm sure many of you have seen it, but some may find it very useful...I did. Plug in your tire size, gear ratio, tranny type and MPH, and it tells you your engine RPM. /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    Looks JUST LIKE randy's that is in the links at the top.
    http://www.ring-pinion.com/calculators/calculatorsind.html
    Wonder who stole from who?
     

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