Forget them all! The 250 engine had the same out put all along, with a slight drop in the 1971 to 1974 versions, and then a regain from 1976 to the last one in the last X-shell Granadas before the 3.3 only Fox 'nada arrived in 1981.
The SAE gross verses net debacle is a suppreme example of how marketing and insurance people make you tell the truth they want to hear without actually lying about it!
1972 was the year mandatory net figues were required in the US. In Australia, it was rolled out from 1976 to 1979, and we had the same issues to content with. (In the USA, it was a result of the Speed Kills campaign of 1971, and the escalating insurance costs since the power race which started in 1958, got 'pliped up' in 1964 with the GTO 389 which had more than less than 10 pounds per hp, and it expolded in 1970 after the outfall from the SOHC, Hemi, and ShotGun 429's gave the muscle cars a tainted killer image).
Both the USA and Aussie 250 were rated at 155 gross from 1969 to 1971, although some smogged versions to cali were less than that. In 1972, every 250 got a 10% drop in power from the US 72 emmission regs, plus an SAE net rating was often 16 to 28%, even 50% less than an SAE gross because the power peak rpm and power was influenced by the ancilaries, exhast and heat correction.
The Aussie 250 went from 155 hp SAE gross in the 1-bbl and 170 SAE gross in the 2-bbl to a measely 123 hp DIN net in 1976. The smog 1976 Aussie 250 engine was much stronger than any earlier 250 1-bbl engine, but it was rated down 26% because the 250 never had 155 hp gross anyway. The 170 hp 250 2v had about 149 hp net, a drop of 14%.
We saw that with the 125 hp 1966 200 Falcon engine which became the much stronger (!) 83 hp 3.3 in 1981. Both cars yielded about 67 hp at the back wheels, and the emission controls loss of 10 to 20% in the power was made up by smarter cam profiles, better rocker arm ratios, much improved intake manifold casting, huge valves and more advanced carburation.
A backgound issue. Fords engines were often not even rated correctly at SAE gross. Sometimes, Ford, GM, or Mopar would take the maximum power rating further down the curve to avoid that dreaded 10 pound per hp insurance premium. So a 380 hp at 5800 rpm Boss 351 was rated at 330 hp at 5400 rpm as it weighed in at 3500 to 3800 pounds, and would get slugged come rego and insurance time.
So on the big engines like the Boss 351, the actual rating was about 330 hp SAE net at 5800rpm, but SAE gross, it was only 330 hp at 5400 rpm. SAE gross at 5800 rpm, it would be 380 hp. See how sneaky things get when you customer pays insurance?
