Reply to "RPM for highway cruising"

Ron O1984/2010 IM, B.C. Canada

I just did a search (transmission ratios) and came across one of my old posts from 2004. In the post I mentioned the numbers for my tranny: R&P is 4.125, and 4th is 0.82. Now I know!!
Using a gear ratio calculator, my engine should be turning 3230 rpm at 70 mph. Using a GPS I found that my engine was turning 3800 rpm at 69 mph.
This can't be right.
That's a difference of over 500 rpm.
Could my Porsche 914 tach be out that much?

12/24/102:04 PM

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