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Factory tach and HEI

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by kiley, Jan 18, 2003.

  1. kiley

    kiley Registered Member

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    I've been reading alot about how a factory tach from my 72 k5 will read to high when I convert to HEI. Is there a filter that will make it ready correctly or do I have to buy a new tach and install it in front of the onld tach on the steering column?
     
  2. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color="blue">Remove the dash and adjust the screw in the back until it reads correct (cant remember if I had to remove the tach from the cluster to do this), use a timimg light for reference. I did this a while ago, I run an EFI distributor with external coil now and it still works fine
     
  3. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    BIG RAY!!!! /forums/images/graemlins/rotfl.gif


    Tsk...tsk..... that adjustment will only correct your tach for a specific RPM....the overall error will still be quite high.

    I had a schematic posted in my gallery for a long time for a simple circuit that will solve the problem. I ran out of space and deleted it....if someone else has it, maybe they can post it....or PM me and I'll e-mail it to you directly.


    Oh what the hell.....here it is:

    [​IMG]


    Oh and here's a post that covered this topic in detail....started originally by "Yours Truly"!!

    http://coloradok5.com/forums/showflat.php?Cat=&amp;Board=firstgen&amp;Number=365281&amp;Forum=firstgen&amp;Words=HEI&amp;Match=Entire%20Phrase&amp;Searchpage=11&amp;Limit=25&amp;Old=allposts&amp;Main=361115&amp;Search=true#Post365281
     
  4. 69K5

    69K5 1/2 ton status

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    thanks for the schem. to bad i cant read it. /forums/images/graemlins/grin.gif but thats why i have my dad /forums/images/graemlins/grin.gif

    nathan
     
  5. TONYP

    TONYP 1/2 ton status

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    I had my bud make that up and it didn't work....need to have him re-do it....
     
  6. kiley

    kiley Registered Member

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    Thanks a bunch. I wasn't looking forward to loosing the stock look inside.
     
  7. Steve_Chin

    Steve_Chin 1/2 ton status

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    You could also put a second generation Camaro tachometer into it. That's what I did with mine and it reads much better than the original tachometer (not to mention that it's useful to where my engine is cammed). It is still not totally accurate (reads high, but not by too terribly much, definitely less accurate than the 1970 Firebird tachometer I have in my Trans Am), but it's better than the stock truck tach. It doesn't look absolutely stock, but if someone glances at it without knowing, they might think that it belongs there.

    There's a picture of it at: http://www.geocities.com/MotorCity/Downs/1963/BlazerPix.html

    Scroll down a screen or two and you'll find it.
     
  8. kiley

    kiley Registered Member

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    Thanks Steve. I remember reading about that on a post last year. Seems like you had a hard time finding the tach you wanted. Did you find it in a junk yard?
     
  9. Steve_Chin

    Steve_Chin 1/2 ton status

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    Yeah, it's a J-yard part. I got it out of a '77 Camaro. I think they changed the style in '78 or '79. If you want a really cool tach, you might want to get one out of a '70-'74 (I think) Camaro. It reads to 8K, where the later one reads to 7K. Those tachs are also repopped. Classic Industries sells the repops. Be warned that you have to cut up the face of the tach, though. I also took the flex circuit out of the Camaro and wired it into the Blazer's flex circuit, and cut the harmonica connector out of the Camaro so that I could properly wire the tach into my ignition.
     
  10. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Kiley,

    Here's another option.....except for being a TON of work, and not being 100% original, you might like it:


    [​IMG]


    I re-used the stock speedo and fuel gauge, but everything else is Autometer stuff. I ended up with Tranny Temp, Water Temp, Oil Temp, Oil Pressure, and a Tach that actually reads correctly.

    Just another option if you want to keep it sorta "stock" looking!!!! /forums/images/graemlins/cool.gif
     
  11. Michael

    Michael 1/2 ton status

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    I think I may have generated that filter schematic...it's from the stock Chevy filter...the one error I see is the cap on the left should be a .15 microfarad, not 15 microfarads. Sorry if this lead anyone astray..... /forums/images/graemlins/blush.gif
     
  12. Michael

    Michael 1/2 ton status

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    Here is a re-draw:
    [​IMG]
     
  13. kiley

    kiley Registered Member

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    Thanks, that looks great. I bought a tach that reads to 8K to strap to the steering column until I feel brave enough to crack open the instrument panel. I'm changing over to HEI on Monday, my first upgrade!I recently bought a 71 c20 longbed for a daily driver and while I was shopping I found a 70 CST that had a factory vacuum guage on the inner right side of the guages, the one that's always blank.
     

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