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Old 09-22-2016, 11:39 PM   #21
Tom Wesenberg
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Default Re: rpm vs. mph

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Originally Posted by cw253748 View Post
I just did Tom's math. I have 14.25 to center of hub cap with 19 inch tires. I get 2675 at 60 mph and 2006 at 45 mph with a 3.78 rear end
If I substitute a 4.11 rear end in the equation I get 2908 at 60 mph and 2181 at 45 mph. So either I have a 4.11 rear end or the tach is off. It is a Westach from Snyders.
Jack up one rear tire, put the tranny in high gear, then count the turns to hand crank the engine until the tire makes 2 revolutions. If you have 4.11 then you will have to crank the engine 4.11 turns. If you have 3.78 then you will have to crank the engine 3 and 3/4 turns.

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Originally Posted by forever4 View Post
Tom,
Did you cipher in the effects of eating too much apple Pi ?
Is it possible to eat too much apple pi?
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Old 09-23-2016, 11:32 AM   #22
160B
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Default Re: rpm vs. mph

Do you know if the speedometer is accurate??

The odometer may be right on with mile markers but the speed cup may not be properly calibrated.

Take a gps with you and see if the speedometer is accurate.
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Old 09-23-2016, 02:44 PM   #23
Tom Wesenberg
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Default Re: rpm vs. mph

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Originally Posted by 160B View Post
Do you know if the speedometer is accurate??

The odometer may be right on with mile markers but the speed cup may not be properly calibrated.

Take a gps with you and see if the speedometer is accurate.
That's what I do. I check the mile markers over a 10 mile stretch, and also look at my GPS for speed. Both the odometer and speedometer are accurate within 2%.
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