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Thread: Tach idle does not match the handheld.

  1. #1

    Default Tach idle does not match the handheld.

    Just installed a Holley Terminator in a customer's car. Running a Holley Dual Sync Distributor, MSD 6A. The handheld screen has the RPM at 920-940, but the Tachometer in the car reads around 1200-1400. Anything that can be done to bring the car tachometer to read the same as the handheld? Maybe some kind of resistor. Thanks, Max.

  2. #2


    Is it an aftermarket tach?

  3. #3


    Hi SatherCS. No, it's a factory tach. DeTomaso Pantera.
    Have a MSD 8920 tach adapter, setup for voltage triggered.
    Italian tach. Thanks, Max.

  4. #4


    My first thought would be to temporarily install a potentiometer inline on the wire coming from the tach adapter, and varying the resistance until it matches up at idle. That will also allow you to verify that it will match up at higher RPM. If that works, then you can take it off and measure the resistance of the potentiometer and install a fixed resistor.

  5. #5


    Hi SatherCS. Sounds like a good idea. I have many of them, I use them for LED lighting. Will let you know how it goes. Thanks, Max

  6. #6


    Tachs work by frequency. A good tach/speedo repair place should be able to make an adjustment.

  7. #7
    Join Date
    Sep 2017


    I also have a DeTomaso Pantera that was also using an MSD 8920, and my tach is ~ 300 RPM out. The Veglia tach is not exactly the most accurate though. Jon Hass at Pantera Electronics calibrates them and there are other companies that gut the innards, install modern electronics, so it looks the same. Jon is also in the process of producing a tach adapter that replaces the 8920, his products are very good. His adapter:
    1. Correct pulse for Veglia tach.
    2. Accepts input from magnetic distributor, ignition system or ECUs. (Shares the magnetic distributor connection with ignition systems and ECUs.)
    3. Provides two outputs, one for Veglia tach and the other for triggering ignition systems and ECUs.
    4. Can also accept trigger signals from crankshaft sensors.
    5. Has integrated LED bar graph display as a RPM reference tach, 1K to 10K RPM in 1K increments.
    6. Indicator for trigger input pulse from distributor or ignition system and ECUs.
    7. Power "ON" indicator.

  8. #8


    Can the A28 wire from the HP ECU for a Terminator EFI system be used for the tach signal? Even though there is an MSD 6A in the setup? I use that wire for COP systems, and Holley Dual Sync Distributors with the HP EFI systems that I've done and it works well. Will it work with the Terminator system for tach signal? Will it need any type of signal booster? Thanks, Max

  9. #9
    Join Date
    Dec 2009


    It depends on the ignition type. You can use the tach output terminal/wire on the MSD CDI box. (Tachometer Signal Information)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  10. #10


    I'm using the MSD tach output now; I've tried both the adapters 8910 & 8920. The tach does work, but the RPM is 200-400 too high on the car, tach compared to the Terminator handheld. Just trying to get a correct signal. So handheld says 920-945 RPM, tach reads 1200-1400 RPM. And thought maybe the A28 wire might do better. Thanks, Max

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