[6pack] tachometer rebuild

[Navarrette, Vance]

        Ian:

        North American TR6s use 3.70:1 diffs. In fourth gear the tranny is
1:1. the only variable is tire size.

        so, 3600RPM/3.70 = 973 RPM for the tires, or 16.2 revolutions per
second.

        16.2rps x (( 2 x ((205mm x 0.70)/25.4mm per inch) + 15inch wheel)) *
3.14) / 12 inches per foot = 111.5 fps.

        88 fps = 60 MPH, so 111.5 fps = 76 MPH

        Sounds like your speedo or tach or both are off. Since you just had
tach rebuilt, it is probably your speedo. If your diff has been modified, to
say 4.10 gears instead of 3.70, then you are running at 68.5 MPH which means
your speedo is probably about as accurate as they get.

        Vance


      Vance Navarrette
    Cogito Ergo Zoom
    I think, therefore I go fast

-----Original Message-----
From: 6pack-bounces+vance.navarrette=intel.com at autox.team.net
[mailto:6pack-bounces+vance.navarrette=intel.com at autox.team.net] On Behalf Of
Ian Breyer
Sent: Monday, September 15, 2008 9:52 AM
To: 6pack at autox.team.net
Subject: [6pack] tachometer rebuild

Hi all. I am hoping you guys can provide some insight.

I just had my tachometer rebuilt by Nissonger Instruments. They did a real
nice job and it is working much better than before. There is no longer any
bounce and it isn't hanging up and jumping all over the place. My only
question is that it use to register 3,000 RPMs in 4th gear when I was doing 70
MPH. Now it is about 3,600 in 4th gear at that speed. Of course I have always
had my doubts about the accuracy of the speedo as well. I am running 205/70/15
tires. The transmission and rear end are stock. No overdrive. Is this normal?

Ian

Ian Breyer
72 TR6 Jasmin Yellow
New Haven, CT
home email: ianbreyer at yahoo.com
work email: ibreyer at hartynet.com
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