I had the same question about my engine, Its a Lycoming o-360 c4f which is rated for 180hp at 2700 rpm, being a fixed prop that on take off can not produce more than 2550 rpm I wondered what the actual HP being being delivered at that rpm was , Lycoming,s website ( and am sure your engine manufacturer will also) have graphs and a matrix that lists the power produced at sea level and altitude at differing temperatures and RPM,s. Mine was 172HP at 2550 RPM at sea level at standard temps.