Had a similar problem with a '6 I recently purchased. First, I'd check the
speedo. At the bottom of the gauge face, there are a set of numbers. It should
read something like 'S/N 6411/02.8 1120'. The last four numbers are the number
of turns/mile for the unit, the first numbers are the Smith's part number. If
you have a different set of numbers, I claim that you have the wrong speedo for
you car. This was the case with my '6; I had a 1000 turns/mile unit and my
odometer and speed was off by 15-20%. Since your odometer is accurate, I would
lay odds that you have correct speedo and the incorrect tach. I assume that the
tach has a similar set of numbers on the face, but don't know what they are.
I'll check at home tonight and see what they say. If this is the case, the
errors should be very linear.
From: Philip E. Barnes [mailto:firstname.lastname@example.org]
Sent: Wednesday, September 16, 1998 10:01 AM
To: Scott.Mackay@intl.sematech.org; email@example.com;
Subject: Re: TR6 engine speeds
"I would suggest double checking your numbers. If the needles still
indicate what you said, line up next to the family grocery getter to verify
you speedo is accurate. If you speedo turns out to be accurate, your tach
must be way out. These cars are notorious for having the incorrect
speedo/tack unit installed."
I have gone through the calcs myself in an effort to come up with a mental
calibration for my speedo. I know that it's way off, but I find that my
seat-of-the-pants feel for speed and moving with traffic tell me that the
tach must also be wrong. Here's what I have found: The odometer is spot on
for general use (+/-1% and only a ralliest would be concerned with that). I
found this by measuring on the interstate over 10 miles or so. Knowing
this, one could hold a steady speed for a good distance and time over that
distance. You now have an average speed to compare to the speedo reading
and could work backward through the equation to come up with an actual
engine speed. It might be too much to ask that the error in the tach and
speedo are linear, but it's a start.
Phil Barnes (firstname.lastname@example.org)
Cortland, NY (nowhere near New York City)
'71 TR6 CC61193L (21 year owner)
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