George Patterson wrote:

It varies from aircraft to aircraft; it's basically the point at which the
engine is putting out 100% rated power at full throttle. It tends to be
somewhere between 6,000' and 9,000'. From memory of the manuals, it's 6,500' for
a Cessna 150J and 8,600' for a Maule MX-7-160.

Me thinks that full throttle power in the 8000' area is 75%.

Ron Lee