Whoa there Brian,
4500 RPM at 70 MPH?!?!? After grinding numerous tire sizes/gear ratios through
my spreadsheets, I would challenge something is very wrong with a TR6 indicating
these numbers. A stock '6 (e.g. stock size tires, stock 3.7:1 diff) will only
be turning ~3250 RPM at 70 MPH, in top gear, no OD. At 4500 RPM, you should be
rocketing at 97+ MPH. 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.
Scott Mackay
Austin, TX
(now turning 3500 at 75 mph regularly!)
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