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      03-11-2007, 06:49 PM   #12
youyou
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Drives: Porsche 997 C4S
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Quote:
Originally Posted by Barat View Post
I think you are confusing the Certified SAE rating with the SAE gross rating:

-SAE gross (used prior to 1972) is the engine output at the crank (no drive train loss) WITHOUT accessories and exhaust/cat (no one uses this one anymore and it's significantly higher than the next one, more or less 10%, because of the losses due to accessories).
-SAE net (used after 1972) is the engine output at the crank (no drive train loss) WITH accessories (this is the 300hp advertised by BMW for the 335 and the hp figure eveyone talks about when comparing cars).
-SAE certified is a new procedure that eliminates some of the areas of flexibility in power measurement, and requires an independent observer present when engines are measured (not very common yet and hp figures can go either up or down compared to SAE net figures).
-you also have brake hp which is commonly used, similiar to SAE net (at the crank no drive train loss), but instead of having ALL accessories tied to the engine only auxiliary components (as the water pump) are connected to the engine. The figure is very slightly superior to SAE net figure.

When power is measured on a dyno it's w(wheel)hp. After compensating for drive train loss ( due to gearbox, diff, heat loss etc...) by dividing by .87 or .85 (man vs auto) in the case of the 335, you get approximately the SAE NET value (since the accessories are connected in your engine in your car).

so supposing that the dyno is accurate all you have to do is divide by .87 or .85 to get the SAE net value.

In the case of modding what is REALLY important is to dyno the car before and after the mod on the SAME dyno (the same day) because what is really important is the delta to measure effective hp gains by REDUCING the number of outside variables. And since not all dyno are as accurate you want to use the same dyno on the same day (to also reduce diff in temp and humidity which can alter the results).

btw all this info can be found here: http://en.wikipedia.org/wiki/Horsepower

I hope this answers your question.

cheers

Thankx Barat.
You and I are going to have a few discussions in Albany
You seem to know your stuff.
Appreciate 0