I have a nice 31 coupe with a 276 inch built flattie with 2 94s and 4 inch crank..I got a spadaro quick change w/4/11 gears with a #24 gear set to make it a 3.15 my 39 trans has a 27 tooth gear set and I am running Firestone 31.5inch diameter deluxe champions....on the free way I run 3 grand at 60 mph with power to spare..according to all the formulas it should be way lower.... Any ideas or suggestions thanks..and yes the gears are in the right way...anybody running a similar set up with better rev numbers....thanks
Something is not correct with your numbers. I would suggest you count the teeth on the quick change gears to confirm the ratio.
I know I checked re-checked and checked again...this is the second set I tried first set came with the quick change and was a number 4 /3.48 that was maybe 55 mph at 3 grand...it runs great...shift it at 3 grand or so and keeps pulling....
Is that a sun tach box on the firewall, I'd be checking actual rpm accuracy first before changing parts around.
I came up with 2031 rpm's at 60 mph with 31.5" dia. tires. Your 4:11 gear should produce 2630 rpm's at 60 mph with 31.5" dia. tires. The '39 trans is 1 to 1 in high gear no matter what first gear it has. Just for comparison, my Highboy turns 2050 rpm's at 70 mph with 3.73 gears and 31" tires in O.D. In 3rd gear, it tachs 2675 rpm's at same speed. Something is way off with your figures.
I burned my brain up doing the formulas over and over getting the same results you guys get...it must be my tach is off it was gone through by williams and the sending unit was converted to electronic...never thought it could be out of adjustment gonna have to dust old sears tach dwell unit out and confirm..thanks for replys..
Who cares what the RPMs are? If the engine is happy, you should be happy. My flathead has a happy spot at 2,600 RPM. A couple hundred up or down and it just doesn't purr like it does at 2,600. Don't know why, so I just try to keep it at 2,600 on the highway (about 68 MPH with my gears and tires).
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