Here is the data:
LOAD HP
37 111.1
39 126.8
42 142.6
46 168.6
52 196.8
58 212.0
96 225.0
From the data in the region of 37 < LOAD < 58, that is, the center portion of the LOAD range, it appears that one could predict the horsepower by the following relationship:
HP = Full-ThrottleHP x ( (0.025 x LOAD) - 0.425)
Testing that function at LOAD = 42 and Full-ThrottleHP = 225:
HP = 225 x ( (0.025 x 42) - 0.425)
HP = 140
This is in a good agreement with the deduced value of 142.6-HP. This relationship does not work if the LOAD is greater than about 60. That is because in the test data used to develop the equation, the full-throttle horsepower appears to be reached when LOAD is about 60. LOAD values above 60 would then suggest the horsepower was greater than the full-throttle horsepower, which is not valid. Similarly the proposed function would return negative values for horsepower when the LOAD was below about 15. Thus the function has a limit to its range of roughly 30 < LOAD < 60, or the mid-range of the LOAD parameter.