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Converter Slip Calculator
Calculate torque converter slip at the finish line
Converter slip is the percentage by which a torque converter falls behind locked-gear math at the top end of a run.
Formula: Theoretical RPM = MPH × 336.14 × total gear ÷ tire diameter · Slip % = (tach − theoretical) ÷ tach × 100
What this number means
This calculates torque converter slip percentage from trap RPM, trap MPH, tire diameter and gear ratio. It compares the RPM you crossed at with the RPM a locked driveline would need for that speed.
What to change next
Typical race converters slip about 4 to 8% at the stripe; a figure climbing past that, or rising over time, points to a converter that is too loose, failing, or a down-on-torque engine. Recheck it after converter, gear or tire changes to build a history.
Worked example
Crossing at 6,800 RPM and 125 MPH with a 4.10 gear and 27 in tire, where locked math needs ≈ 6,380 RPM, gives ≈ 6% slip.