| Moderated by: Greg Fletcher | ||
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upstate mike Member
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Hi, the more I drive my 4 speed 74 JH the better the tach seems to work. The previous owner didn't put alot of miles on it for the years I have his service records for. Anyway I'm wondering how accurate my tach is reading 3000 rpm at 60 mph in 4th gear . Thanks in advance, Mike K |
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edward_davis Member 
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Mike, if you have the stock 185/70HR13 tires, the circumference of the tire should be about 6 feet. At 60 mph, you're going ~90 feet per second, which works out to about 900 rpm for the wheels. With the stock axle ratio of 3.727:1 and the 1:1 top gear, the engine should be going about 3350 rpm at 60 mph. The stock JH tach often has difficulty with rpms in the midrange, but ~300 rpm is good for 30 year old electronics. |
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upstate mike Member
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Thanks for the info, Mike K |
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