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    Author Topic: Rallye tach reads differently each time out  (Read 557 times)

    Offline tommyg29

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    Rallye tach reads differently each time out
    « on: September 13, 2009 - 07:38:48 PM »
    The last few times I took the car out on the highway I recorded the mph/rpm. A few weeks ago it recorded 3200 @ 60mph and 2700 @ 50mph. Today it was 3300 @60 and 2600@50. A couple months ago it was about 3700@60 and 4200@70.
    I have an msd tach adapter, and I checked the speedo against a radar. The speedo says 30mph when actual is 27mph, and I confirmed this by running an exact mile and recording 1.1 miles on the odometer. Obviously the speedo is not calibrated with the rear tires.
    Any ideas?
    Thanks.
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    72 Roadrunner 400-4 Auto-3.23 Gear-Black Cruiser
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    Offline dodj

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    Re: Rallye tach reads differently each time out
    « Reply #1 on: September 13, 2009 - 07:53:45 PM »
    For the speedo calibration, you need to check the diameter of the rear wheels with the speedo gear you are running. As far as the tach reading a different RPM for the same speed..... :dunno:
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    Scott
    1973 Challenger  440 4 spd 
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    Offline 73Chally

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    Re: Rallye tach reads differently each time out
    « Reply #2 on: September 13, 2009 - 07:59:42 PM »
    Do you have a new tach board, or is it an original tach?  If it's the original board, a new board would be a very wise investment, and money well spent.
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