Tach. readings changed with HEI conversion

Discussion in 'Small Block Tech' started by cray1801, Apr 19, 2002.

  1. cray1801

    cray1801 Too much is just right.

    I sent my factory in-dash tach. out to have it re-furbished about eighteen months ago. I had it configured to be compatible with both points and electronic ignition. Well since the switch to HEI I've noticed it reads low, maybe 75% of what it should.

    Could this be due to the change in voltage that is sent to the HEI? I will contact the vender but thought I'd post here to see if anyone has had this happen and how was it corrected? I sure hope I don't have to dis-assemble the dash again
    :Dou:
     
  2. GSXMEN

    GSXMEN Got Jesus?

    Is it possible for it to be calibrated for a 6 cylinder?? Just happens to be 25% less cylinders.

    Scott
     
  3. cray1801

    cray1801 Too much is just right.

    It was correct (or close to it) with the points dist. :Do No:
     
  4. sbbuick

    sbbuick My driving scares people!

    I wish that I had a definite answer for you, but I do have some suggestions.

    If the tach is correct with points, then it has an issue with the type of signal it's getting from the TACH output on the HEI.
    Is it a stock HEI unit?

    I'm having a weird problem with the Year One factory dash tach.
    The thing seems fine until I hit 4500 rpm. Then it goes crazy.
    I have an HEI with the extreme duty Accel module in it.

    Year one has two tach adapters. I personally feel that they are $ marked up too much, but I think that they might help you.
    They basically take the tach output from your HEI and condition it, or change it altogether into the simple, basic "square" type wave signal. The same that a point ignition produces.

    I'd ask at your local speed shop. MSD makes these Tach Adapters. IF not, then try asking someone at Year One.

    Just my $.02.

    BTW, that is a fine looking '72 !
     
  5. cray1801

    cray1801 Too much is just right.

    Well I sent the tach. repair guy a nice letter including pictures of the inside of the tach. along with and my original receipt. I asked if there was an oversight and the HEI modification was not done? He said, "Send me the tach. I think I know what the problem is" (so do I, it was never done).

    I'm sure if I had written the letter with my emotions :af: :af: :spank: , I would have gotten nowhere, as it's been over a year (past the warranty period). I've learned it's often best to crack the door so the **** can get out without stirring it up, a lot less stink that way. :Smarty:
     

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