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speed vs rpm

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Old 04-08-2012, 08:34 AM
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speed vs rpm
i have a 1989 d250 with a 727 automatic.307 rear.235 85 16 tires(31"tall).i just put a tiny tac on the truck.the tac reads 2250rpm at 65 mph.does this sound correct?any help will help! thanks.
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Old 04-08-2012, 08:44 AM
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Originally Posted by cseby
i have a 1989 d250 with a 727 automatic.307 rear.235 85 16 tires(31"tall).i just put a tiny tac on the truck.the tac reads 2250rpm at 65 mph.does this sound correct?any help will help! thanks.
I have a 93, D350, does about 1800 rpm at that speed with the same tires. Calculating the gear ratio differences, I come up with 2249.63 rpm

So I'd say yer right on.
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Old 04-08-2012, 10:33 AM
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With 235's you should be right at 2000 at 60 MPH.
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Old 04-09-2012, 08:18 AM
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My 90 5" tac shows 2050 rpm at 60, but will change a little going down hill or up
because of the 727 trans slip with 235/85/16 tires.
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Old 04-09-2012, 05:32 PM
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I will have to double check but at 60 I run about 1850 with my gear vendor...

I double checked the above and I actually get about 1750 to 1775 going 60 mph with the Gear Vendor engaged.
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Old 04-10-2012, 07:12 PM
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bruce M,what kind of tac do you have?
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Old 04-11-2012, 09:15 PM
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Philip is spot on. My calc's say 1995 rpm at 60 not accounting for slippage, so 2K at 60/2200 at 65 is on the mark.
I use a tiny tach also.
 
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