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how acurate are stock tachs

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Sparky, Nov 18, 2001.

  1. Sparky

    Sparky 1/2 ton status

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    How acurate are the older stock Chevy tachs? As in from 78. At idle my trucks tach reads around 600 RPM, but by ear it sounds a little higher. More like about 700-800. And, if i turn up my idle to where it reads at 700 in gear 800 out of gear it wants to diesel. Additionaly, if i use one of those handy online rpm calculaters it says my rpm on the highway in 3rd at 70 should be somewhere around 2500, but my tach always reads around 3000 RPM at 70. I know my automatic will loose a little, but not 500 RPM right? More like 200 or so from what I have heard. So I was thinking they are off at idle by maybe a 100 rpm or so and are off by up to around 300 at higher RPM. Anyone know for sure about how acurate they are? Heck, the Furd tachs in the fox body mustangs are off by more like 500 rpm in the upper rpm range. I guess I can complain with my Cevy tach being off by 300 considering it is 20 yrs. older.


    Sparky

    When all else fails... Check the blinker fluid.
    78 K-5
     
  2. Slayer

    Slayer 1/2 ton status

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    Whatdayaexpect from a 23 year old piece of equipment. I ran a hell of a lot better 23 years ago.
    Actually I now believe that Auto Meter gauges are the way to go, and I'm hoping that Santa is checking them out for me. Plus, an aftermarket tach looks cool bolted wherever you want..................

    <font color=blue>I don't know everything, I just think that I do.............</font color=blue>[​IMG]
     
  3. Sparky

    Sparky 1/2 ton status

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    yeah, i agree. I cant complain with it being off, but I was just wondering what everyone else with stock tachs says. There is some piece of mind in knowing what other peoples tachs are doing.

    Sparky

    When all else fails... Check the blinker fluid.
    78 K-5
     
  4. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    The factory in the Lady's 79 is a bit optomistic. Truck is on 31's, 373 in the pigs. 75 mph it reads about 8k. that's a hell of a crate engine I got there huh? LOL. It points straight down. At idle it reads 1100 when I know the engine is turning about 600.

    Women dig dents and flat paint!
    coloradok5.com/gallery/Grim
    75 Jimmy, Dollar
    Grim-Reaper
     
  5. DesertDueler

    DesertDueler 1/2 ton status

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    Gotta love stock tachs :) Most are off by about 500 rpms from 3000 on up. Get an autometer and youll be happy.

    86Jimmy 4"&35"MTRs,87 burb 4"&35"MT,69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    I've had needles come loose on the speedo, the tach could be the same way. (don't break it though lol) Borrow someones aftermarket tach and rig leads up for it, and compare at the same speeds/idle yours reads, and see how it stacks up. Mine appears to be reading perfectly, if I had a 6 cylinder : )


    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
    Why insist on counting when the ring gear has the tooth counts stamped in?
     

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