All HOT max ratings are measured at 6,000 alternator RPM, which is roughly 2,000 engine RPM depending on the vehicle's pulley ratio.
All HOT idle ratings are measured at 1,800 alternator RPM, which is roughly 600 engine RPM depending on the vehicle's pulley ratio. This idle rating covers 99% of vehicles made and more than likely, you will see higher ratings than we have posted.
Most pulley ratios are around 3:1 (6" diameter crankshaft and 2" diameter pulley).
To find your vehicle specific pulley ratio and rough estimate of how much power your alternator is making at a given engine speed, use the following formula:
Crankshaft Pulley Diameter / Alternator Pulley Diameter = Pulley Ratio
Pulley Ratio * Engine RPM = Alternator RPM
***These ratings are much lower than our competitors who rate their alternators at an idle speed of 2,500 alternator RPM and a peak speed of 8,000 alternator RPM. Many of their tests equal 833 idle engine RPM and 2,667 engine RPM. ***