New H.P. VS old H.P.: What's the deal again?

[and00542]

If a 340 block produced 240 H.P.'s and 340 lbs of torque, what would be the equivalent using the "new" formula today. I was told that it was approximately New HP=Old HP / 0.8. Is this correct?

[DartGT66]

The rating changed at '72, so a 240 hp 340 should be 240 hp even by todays standards.

[jimmycarter]

i believe new engines are tested without the transmission and differential connected. old horsepower / 0.8 or maybe 0.85 is probably about right.

[DartGT66]

The factory measured horsepower has always been crank horsepower. Before '72 there was no accessories in the engine, ie. alternator, water pump, exhaust, air filter assembly etc. The numbers were also "coloured" slightly either upwards or downwards. So, to convert old horsepower to new ones isn't that easy, there are too many variables. At least one thing is for sure; to convert old hp to new ones you do not divide the number by 0.8, maybe multiply but not divide.

[and00542]

.... You're absolutely right DARTGT66. In my original posting, I should have written 1 New H.P. = 1 old H.P. * 0.8.

Thanks everyone, as long as we all agree that it should be around 0.8.....