Since most agricultural equipment manufacturers have historically used PTO power when advertising a tractor's power output, it is important to understand the difference between engine/flywheel horsepower and PTO horsepower when determining what engine power to target for a conversion. To demonstrate the difference, we'll use the White model 100 tractor as an example. The University of Nebraska tractor test results rated the White 100 at 94 PTO horsepower at a PTO speed/engine speed of 540rpm/2400rpm. Because of drive line frictional losses and parasitics, the engine flywheel power required to generate 94 PTO horsepower is actually greater than 94 horsepower. In this example, the actual engine output is 102 horsepower at 2400rpm, or 8% higher than PTO horsepower. A fair assumption for the general frictional losses found in most Oliver/White PTO drive lines is around 8-10% or put another way, roughly 90% of engine power is available at the PTO.