Average RPM slippage on a conv

[S/ST 3040]

Originally Posted by ken robinson

Whats the average rule of conv. slippage = in RPM +/- ? I'm trying to see what the top end RPM is with different rear gear ratio's .... RPM x tire dia. / by MPH X 336 = ring & pinion ratio . That formula dosen't account for conv. slippage , and is giving me the wrong gear ratios ....The car goes thru at 6750 x 28 tire / average 115 mph x 336 = 4:85 gear . But thats not true because it runs a 4:30 not a 4:85 . What would it go though with 4
:56 like 7150 rpm in average air ? My math / formula is wrong or I'm missing some thing .

115 x 4.30 x 336 / 28 = 5934 RPM (drive shaft RPM)


5934 x 100 = 593400 / 6750 = 87.9% (or 12.09% slippage)


115 x 4.56 x 336 / 28 = 6293 (drive shaft RPM)


6290 / .879 = 7159 RPM


The 4.56 gear should let the converter show better efficiency but, no way of knowing
exactly how much. Like was already stated, tire growth will affect the final number.