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308 tach substitute

Discussion in 'Technical Q&A' started by Doug, Feb 4, 2005.

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  1. Doug

    Doug Formula 3

    Nov 13, 2003
    1,473
    Louisville KY
    Full Name:
    Doug
    #1 Doug, Feb 4, 2005
    What is the difference between an early 308 tach that is set up to run off dual dist. and a later tach set for 1? Could I substitute a 308 GTSi tach on my 308 GT4 that has been converted to a single electronic dist. to alleviate the double rpm reading?
     
  2. Birdman

    Birdman F1 Veteran

    Jun 20, 2003
    6,689
    North shore, MA
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    THE Birdman
    #2 Birdman, Feb 6, 2005
    I may be wrong but I'm pretty sure you can have the tach converted to run with a single distributor by palo alto speedometer.

    http://www.paspeedo.com/

    Birdman
     
  3. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
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    Russ Turner
    #3 snj5, Feb 6, 2005
    308 with two ignition coils use a tach that is essentially a 4 cylnder engine tachometer that follows one coil firing to give rpm. A stock 308 GTSi still has two coils, and takes a signal from one of the two ecus as a driver for a 4 cylinder tachometer.

    Birdman is exactly right that Palo Alto can convert your tach to a single coil, single distributor 8 cylinder tach quite easily. In fact, Norwood's single distributor kit also converts the '4-cylinder tach' into an '8 cylinder tach' so the path is actually well trodden.

    hope this helps
    rt
     
  4. Doug

    Doug Formula 3

    Nov 13, 2003
    1,473
    Louisville KY
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    Doug
    #4 Doug, Feb 6, 2005
    My mistake. I thought that the FI models went to a single dizzy/coil. I would prefer to not convert mine because that way if someone wanted to go back to original dual dizzy, the tach won't have to be converted back.
     
  5. gerritv

    gerritv Formula 3

    Jun 18, 2001
    1,400
    St Catharines
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    Gerrit
    #5 gerritv, Feb 6, 2005
    Hi Doug
    If you have two coils, then there should not be a need to change the tach.
     
  6. Doug

    Doug Formula 3

    Nov 13, 2003
    1,473
    Louisville KY
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    Doug
    #6 Doug, Feb 6, 2005
    My car has been converted to single dizzy so my tach runs double if hooked up.
     
  7. DGS

    DGS Seven Time F1 World Champ
    Rossa Subscribed

    May 27, 2003
    72,986
    MidTN
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    DGS
    #7 DGS, Feb 7, 2005
    If your tach is getting its reading directly from a tach connection on the new ignition computer, a software update could fix the reading.

    Or you could get a electronics hobbyist to mung you up a divide by two circuit.
    (Not an engineer -- most engineers work on paper. Only a few nuts like me have ever etched a circuit board themselves. ;) )
    (Alas, my board etching supplies were packed by the movers -- I may never find them.)
     

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