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Old 01-16-2009, 10:04 AM   #22
fastenova
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Member#: 38829
Join Date: Jun 2003
Chapter/Region: NWIC
Location: Tigard, OR
Vehicle:
Not your usual 1997
Legacy GT

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Quote:
Originally Posted by zavier View Post
i thought the HP difference was not because of a tune but because of a change in how the HP is rated...didn't the standards change between 2007 and 2008?
Quote:
Originally Posted by watchunglava View Post
really so since Watt it has been the same but now it's different?

The following definitions have been widely used:

Mechanical horsepower
hp(I) ***8801; 33,000 ft·lbf/min
= 550 ft·lbf/s
= 745.6999 W

Metric horsepower
hp(M) ***8801; 75 kgf·m/s

= 735.49875 W (exactly)

Electrical horsepower
hp(E) ***8801;746 W
Boiler horsepower
hp(S) ***8801; 33,475 Btu/h
=9809.5 W

Hydraulic horsepower =Flow Rate(US gal/min) * Pressure(psi) / 1714
The definition of HP is not what is in question. That is a constant in today's world.

What was said was that PEAK torque and HP changed between the two years. HP and torque are both dependent on engine RPM, so that's your X axis. What is important is that Subaru has changed the shape of the graph (through tuning such as timing and fuel trim adjustments, and/or mechanical adjustments, such as a different cam profile) in a way that a sacrifice in PEAK HP has created an increase in peak torque.

Hopefully, these changes raised torque everywhere, as peak torque is not nearly as important as the torque band, or "area under the curve" as many like to say. This provides for more drivability under 'normal street' conditions. Just as drag cars are concerned with peak numbers because they are geared for the highest possible output over a quarter mile, most street vehicles are more concerned with numbers in the 1000-3000 RPM range, as that is where they operate most frequently.

What was also said is that the way HP is measured in SAE tests (which is the standard for bhp and torque measurements in the automotive industry) changed. However, I am not sure when Subaru started listing their numbers as SAE-certified.

watchunglava, since I can see you like Wikipedia, scroll down on the same page you got the HP defs from and look at SAE certified HP. zavier, prior to 2005, SAE net horsepower was used starting in the early seventies. Since it's a voluntary change in measurement, Subaru could have started with MY2007, but I have no evidence of that. Some manufacturers lost HP, some gained, and even looking at the same manufacturers, certain engines lost/gained power. However, the shape of the curves would remain relatively the same.

I have been wondering about the SAE changes myself for a while, so thanks for providing me with the motivation to research it myself!

Here's the link to SAE's web site detailing certified power: http://www.sae.org/certifiedpower/

Cheers,
Aaron
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