First you should measure the circumference of your tire and then
calculate the RPM the engine is turning. According to
www.powerdog.com/tiresize.cgi, a tire calculator, 205 - 60 - 13 has a
circumference of 71.3" and the wheel turns 889 revs/mile. For this
tire and the 3.07 gears you should see;
60 mph = 2729 rpm
70 mph = 3183 rpm
87.9 mph = 4000 rpm
You should now check the calibation of your Tach against a good hand
held tach. The stock tach can be adjusted. There is a
potentiometer inside the Tach that can be reached through the hole for
the lamp. Adjust the tach for accuracy in the 2000 rpm to 3000rpm range.
The next problem is the speedometer, if it is stock , it probable is
not the correct ratio for these tires. You need to know what gear is
on the speedometer cable, stock is 15 teeth, and you need to know the
speedo, revs / mile. The speedo has a number on the face , I have
seen 980,1000, and 1020. The best ratio I can come up with for this
tire, gear combo is a 1020 speedo, and a 16 tooth cable gear.
Will a 260 run all day at 4000 rpm. Yes it probably will, but it will
wear out sooner. Lower rmp = lower wear. I'm not sure what
information is on page 65-67 of the Performance Tuning, please share
the info you are referring .
Ron Fraser
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