SAE correction factors make ESTIMATES of the power used to drive auxilliary components, water pump/fan/air con/pwr steer/air cleaner etc.
Until someone puts their engine on an engine dyno, and quotes the actual air temp and pressure at the time the raw figures were obtained, we will only have estimates.
A chassis dyno is a tool to show a customer the difference between what he came in with and what he drove out with, nothing more - nothing less, too many estimates and fudge factors.
How about we stop kidding ourselves that mine is bigger than your's!
Gee, I must be getting a grumpy old busted :swordfight:
The Society of Automotive Engineers (SAE) has created a standard method for correcting horsepower and torque readings so that they will seem as if the readings had all been taken at the same "standard" test cell where the air pressure, humidity and air temperature are held constant. Furthermore, the standard includes an assumed mechanical efficiency of 85% in order to provide an estimate of the true engine horsepower (without accessories).
SAE J1349 Update:
In August 2004 the SAE released J1349 Revised AUG2004 which specifies that the preferred method of determining the friction power used by the motor accessories is actual measurement, and that the assumption of 85% mechanical efficiency (as formerly used in SAE J1349 Revision JUN90) should only be used when actual friction data are not available.
The equation for computing brake horsepower, assuming 85% mechanical efficiency, was very slightly revised .
The AUG2004 revision also makes it clear that this correction factor is not intended to provide accurate corrections over an extremely wide range, but rather that the intended range of air temperatures is 15 to 35 deg C, and the intended range of dry air pressures is 900 to 1050 mb.