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  • Speedo verified w/GPS.

    After changing the gears from 3.08 to 3.73, and having the PCM updated (by PCMFORLESS.COM) I had the opportunity to check the speedo with Garmin GPS. Speedo is reading dead on right up to 70 mph. That's as fast as I was able to get in this morning's rush hour traffic.

    Was pleased to know that the update is accurate, and there are no issues.

    Just thought I'd pass that along.

  • #2
    Re: Speedo verified w/GPS.

    I still havent corrected my speedo... but as far as i know, i switched to 3.73's aswell and its reading 10% off, once i have my car tuned i will probably mention it
    Wait, Is that a V6 or V8?
    1990 Chevrolet C-K 1500 series 4.3L .. 5spd
    1994 JDM Euno Roadster 1.8L 5spd Bolt Ons.. etc
    2000 Camaro 3.8L Auto Bolt Ons..etc

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    • #3
      Re: Speedo verified w/GPS.

      I have a 3.43 right now, and I’ve thought about switching to a 3.73 for a while now.. how hard was the install?

      Comment


      • #4
        Re: Speedo verified w/GPS.

        my garmin has always lagged on speed, but i suppose with cruise control that would work well (no speed changes).

        what RPM were you running at 70 with the 3.73s?

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        • #5
          Re: Speedo verified w/GPS.

          I was at like 1900 going 60 mph so probably around 2100 i think, maybe even more, havent driven the camaro in a while.
          Wait, Is that a V6 or V8?
          1990 Chevrolet C-K 1500 series 4.3L .. 5spd
          1994 JDM Euno Roadster 1.8L 5spd Bolt Ons.. etc
          2000 Camaro 3.8L Auto Bolt Ons..etc

          Comment


          • #6
            Re: Speedo verified w/GPS.

            Off Topic but if the speedo is off because of gears or tires or w/e is the odometer off as well?

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            • #7
              Re: Speedo verified w/GPS.

              i thought that in our cars the speedo/odometer were mechanically driven and that the PCM wasnt the only thing that needed to be corrected?

              Comment


              • #8
                Re: Speedo verified w/GPS.

                Originally posted by silVerSIXf-body View Post
                I have a 3.43 right now, and I’ve thought about switching to a 3.73 for a while now.. how hard was the install?
                I shopped around and got quotes from a few garages. Went with one that builds race cars. I think it was about $300 or so for the whole job, and I supplied all the parts, including gaskets and seals.

                Originally posted by venom3300 View Post
                my garmin has always lagged on speed, but i suppose with cruise control that would work well (no speed changes).

                what RPM were you running at 70 with the 3.73s?
                There is a jump in RPM's, but not too excessive for me: 1900 rpm was 65 mph w/3.08, now 2300 is 65 w/3.73. 70 is 2500 75 is 2650 rpm, 80 is 2800, 130 is 4600 rpm.
                Originally posted by timthescarred View Post
                Off Topic but if the speedo is off because of gears or tires or w/e is the odometer off as well?
                Originally posted by Niko97RS View Post
                i thought that in our cars the speedo/odometer were mechanically driven and that the PCM wasnt the only thing that needed to be corrected?
                The 4th gen F-body speedo and odometer are driven by the PCM, (based on engine RPM, trans gear, rear ratio and tire diameter) so changing anything in the drive train, (gears, wheels, tires) will cause the speedo to be off.

                Its easy to project your RPM at speed for gear changes. Take the difference between the ratios as a percent (3.73 / 3.08 = 1.21 or 21%) Add 21% to the RPM to get the new RPM (1900 + 399 = 2299)

                The whole gear/posi upgrade is here: http://shareaproject.com/pages/projectTut,p,550,00.html
                Last edited by Mark42; 02-22-2011, 09:24 PM.

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                • #9
                  Re: Speedo verified w/GPS.

                  Thank you for that formula mark
                  Wait, Is that a V6 or V8?
                  1990 Chevrolet C-K 1500 series 4.3L .. 5spd
                  1994 JDM Euno Roadster 1.8L 5spd Bolt Ons.. etc
                  2000 Camaro 3.8L Auto Bolt Ons..etc

                  Comment

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