Gross Horsepower vs. Net Horsepower
Thru July 1971
The Car Manufacturers measured Horsepower by using a test rating methodology set by the
Standard of American Engineers {S.A.E} {Code J1349}
This calculated the ouput of a 'bare' Engine on a test stand. With no accessories or belts.
And with 'optimal' timing, adjusted carburetion, free-flowing exhaust and with a correction factor
for atmospheric conditions.
In other words, 'unrestricted' advertised Gross Horsepower at the Flywheel.
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In August 1971 {for the 1972 Model year}, the Horsepower Rating was changed to {J245 and J1995}
testing methodology.
Now, the Engines were tested with the 'accessories' bolted on the Engine {ie; Water Pump, Fan, Alternator
and Air-Pump, and with the Pulley-Belts installed}.
Also, the timing was 'not' adjusted {advanced} for optimal Horsepower Output, and the Carburetion was
not 'tweaked' for optimal Air/Fuel mixture.
This gave a 'more true' like driving condition Horsepower Rating.
Horsepower was still measured at the Flywheel.
This new testing effected the Gross Horsepower 'read-out' by approximately {10% to 12%}, though it was
the 'same' identical Engine.
Now, add in the fact that the 1972 Engines were equipped with 'lower' Compression Pistons, and early emission
controls {A.I.P. = Air Injection Pump} and {E.G.R. = Exhaust Gas Recirculator} to create a 'de-tuned' Engine,
which lowered Horsepower by another 6% to 8%.
