Quote:
Originally Posted by priobe
olddog,
Excellant point. Next time I take the car out I will monitor low rpm and at what speed.
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Not knowing what your transmition is, I suggest you settle the tach on 2000 rpm in top gear. Shift down a gear and see how many rpm you turn to match that speed.
Also find the lowest speed the engine will pull at smoothly for a long while. I'm assuming that will be somewhere near but south of 2000. Add the rpm change from shifting down a gear to this number. For example if the rpm change is 1200 when you shift down a gear and your minimum operating rpm is 1600, then shifting down a gear will give you 2800 rpm. That will be your choices (1600 or 2800) at the critical speed where you can go no slower in top gear. You really don't want that point to be at the speed you drive the most.
The method I described is not perfectly accurate, but certainly will be in the ball park. Shifting down at the minimum operating rpm would be more accurate, but trying to read a tach to 50 rpm while driving can be difficult and create errors, as well.
Take what you find and compare to some of the calculators you found. Good luck.