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What is the target RPM for a tbi 350 (STOCK) to run on the highway in OD

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

  1. jjlaughner

    jjlaughner 3/4 ton status

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    I'm doing some calculations on the gears/tires I have now, vs gear tires of stock, vs what I need. SO, I'm curious what the target RPM for the engine in an 87 blazer is to run so that its in lockup/overdrive. I know if you have 32's and 3.08's it doesn't like to stay in OD very well /forums/images/graemlins/whistling.gif (providing cruising speed is 70MPH (55-65 is fine)


    With that said I dont want you should run this gear with this size tire posts... I'm looking for what the operating RPM for OD is? /forums/images/graemlins/ears.gif /forums/images/graemlins/ears.gif /forums/images/graemlins/ears.gif /forums/images/graemlins/ears.gif
    80% of use is 65-75mph range, the other 20% is stop and go under 30mph /forums/images/graemlins/deal.gif
     
  2. jjlaughner

    jjlaughner 3/4 ton status

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    is there one of these for OD tranny's?
    Gear table at 4lo.com


    Nevermind, if you take the target good highway speed in Yellow for the std 1=1 trany
    35/4.11 @ 1=1 =2565 (for the non-overdrive)
    and multipul it by .7 for the overdrive
    35/4.11 @ 1=.7 it would be 1795 for a target highway gear

    Do I still need to shoot for a 2000 RPM range for the OD to kickin? /forums/images/graemlins/confused.gif
    so I guess again I'm wondering what the target RPM rate is for the Overdrive to function?
     
  3. husurddy

    husurddy 1/2 ton status

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    Click
    /forums/images/graemlins/thumb.gif
     
  4. parker

    parker Registered Member

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    I run an over drive tranny in one of my trucks 700 r4
    with 32 inch tires and 3:73 gear in the diff and get about
    2300 rpm @70 mph which I think is good because its enough rpm that it dosent have to shift every time you see a hill and low enough to still get desent gas milage.
     
  5. Jays Beast

    Jays Beast 1/2 ton status

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  6. Hossbaby50

    Hossbaby50 3/4 ton status

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    I run 2200 in OD with TPI. It is pretty good for me. I personally would like a little more gear to bump my motor more into its power range. 2400-2600 would be fine by me for 75MPH. For me that would be 4.88 or 5.13 gears with my 35's.

    Harley
     
  7. heavy4x4

    heavy4x4 1/2 ton status

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    [ QUOTE ]
    I run an over drive tranny in one of my trucks 700 r4
    with 32 inch tires and 3:73 gear in the diff and get about
    2300 rpm @70 mph which I think is good because its enough rpm that it dosent have to shift every time you see a hill and low enough to still get desent gas milage.

    [/ QUOTE ]

    Uh, the only way you'd be running that rpm at that speed with that setup is if you weren't in lockup and the tranny was slipping a lot.
    I've got basically the same setup (running 33's though), and I'm running about 1900 rpm at that speed in OD-lockup. No way are you running 2300...although I do agree, that would be ideal.

    (If you are indeed in OD-lockup, then you've got closer to 4.56's)
     
  8. Hossbaby50

    Hossbaby50 3/4 ton status

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    or shorter actual overall height of his 32's. I had 32's (31" actual) with 4.56's and cruised around 2700 or so I believe it was at 70ish.

    Harley
     
  9. Thunder

    Thunder 3/4 ton status

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    I run around 2000-2100 at 75 mph with 3.73/33" MTs. I like the way my engine runs there. I get real good gas mileage at 2000 rpm. The Convertor is locked up, Foot is barely on the throttle, Have plenty of power. Once in a while when fighting a strong head wind the convertor will unlock. It also unlocks on hills as it should.
    But I also built my engine to run real good at cruise speed.
    I usually cruise at 70-85 mph. My gas mileage drops off significantly after 2400 RPM.
     
  10. 87BrnRsd

    87BrnRsd 1/2 ton status

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    I have an 87 K5 and am running 4.56 gears and 37" tires. Cruising on the highway at 70, my rpm's are at about 2300. That is a good rpm range for me. Doesnt really kick out of od on hills, unless they are huge. Ive had it up to about 85-90 before and was only running like 25-2600. Then again, its hard to tell exactly what speed im going because the 4.56 gears screwed the speedometer all to hell. /forums/images/graemlins/ignore.gif
    -Harrison
     

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