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Tachometer/Speedometer accuracy?

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  • Tachometer/Speedometer accuracy?

    My dyno guy commented that all Nissan tachometers are a couple hundred RPM optimistic and, comparing the tach to my Apexi NEO, that statement appears to be true. I've also noticed that my JWT ecu redline of 7200 kicks in at an indicated 7400 on the tach.

    I hadn't really thought about the speedo until last weekend when I did a PDX at Road Atlanta. I'm running a DOHC cluster with the digital speedo but the car is built from a mish-mash of E/DE/S13/S14 parts I've collected and I don't really know what the speedo sensor came from. Anyway, I had a blast at RA but found it harder than I expected to hit the 95MPH limit on either the front or back straight (?) I just got around to unloading the car yesterday and put the stock wheels back on for some testing. I took it for a ride and the speedo indicated 62MPH at the rev limiter. My calculator says that I should be at 68MPH at (7200 on the NEO) on stock size tires. If it's 6MPH low at that speed it would be almost 10MPH low at 100MPH. I know most speedo's are 2-3% high to protect us from ourselves but mine is about 10% low. Is it common to be off this much or do I have the wrong speed sensor in my transmission? I'm running the stock 4.08 final drive.
    Last edited by djsilver; 06-02-2010, 09:13 AM. Reason: more info
    Don Johnson (really!)
    Just so you know.

  • #2
    All the s13 speed sensors are the same, so it shouldn't matter.

    I know my tach and speedo on the cluster differ from what my PowerFC says.

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    • #3
      Last time I hooked my car up to my OBD-II scanner, the RPM on my tach was within 50 or so (1/2 a division) up to about 6000rpm. after that point, I concentrated more on my driving.
      Originally posted by SoSideways
      I don't care what color they are as long as they are LONG AND HARD.
      '04 G35 Sedan 6MT- The DD
      '96 240SX- The Track Toy

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      • #4
        My tach seems pretty accurate compared to the Integra I had a long time ago. It doesn't keep up with the engine in 3rd gear or below when running high boost, but I can live with that. Makes me think it's hella fast when the electrons can't keep up with my acceleration y0!
        '18 Chevrolet Volt - Electric fun hatch for DD duty!


        DefSport Koni Sleeve and Spring Perch Buy!!!
        http://www.nissanroadracing.com/showthread.php?t=5902

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        • #5
          I don't have an issue with my tachometer, however my speedometer is about 8MPH off around 70MPH and I haven't bothered checking any higher than that. I know it gets worse and worse as I increase in speed. I am running stock size wheels/tires for a 1991 240SX.

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          • #6
            When I did a dyno, My tach was reading almost 500 RPM high compared to the dyno.
            Chicago Region SCCA SM # 688 http://www.scca-chicago.com
            TSSCC SM # 688 http://www.tsscc.org

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