Question.
Melting Slicks
Joined: Sep 2006
Posts: 2,976
Likes: 1
From: Santee California
The advertised horsepower is at the flywheel. The ones you see quoted on the Forum are at the rear wheel. This is always less than at the flywheel, but can be measured without removing the engine from the car. The rear wheel number is useful for evaluating the increases from aftermarket mods.
Pro
Joined: Nov 2003
Posts: 505
Likes: 0
From: Childersburg/Talladega Ala
As a side note, and gentlemen correct me if I am wrong. In the late 60's and early 70's the manufacturer's temporarily changed to rear wheel HP #'s to fight the insurance companies expensive policy on high horse power cars. I'm not sure when they changed back to flywheel ratings.
Drifting
Joined: Feb 2006
Posts: 1,378
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From: I don't deserve this car, but I have arthritis and I don't deserve that either. Bay Point, FL
St. Jude Donor '06-'07
Melting Slicks
Joined: Jan 2007
Posts: 2,633
Likes: 2
From: Evans Colorado
As a side note, and gentlemen correct me if I am wrong. In the late 60's and early 70's the manufacturer's temporarily changed to rear wheel HP #'s to fight the insurance companies expensive policy on high horse power cars. I'm not sure when they changed back to flywheel ratings.
However, what they did use for a long time was SAE gross power which was engine power before the accessories such as the alternator, AC if applicable, power steering etc was added to the engine.
When the switched to SAE net the power numbers decreased because now it was with the accessories mounted on the engine.
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Instructor
Joined: Jan 2006
Posts: 170
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From: Sioux City Iowa
St. Jude Donor '06
1972 switched from gross to net horsepower, and conincidentally dropped compression the same year. By 1973 they should have taken new cars directly from the factory to the crusher. 
Team Owner
Joined: Oct 2004
Posts: 27,420
Likes: 64
From: San Clemente CA
On the right track, but manufacturers as far as I know have never used RWHP figures.
However, what they did use for a long time was SAE gross power which was engine power before the accessories such as the alternator, AC if applicable, power steering etc was added to the engine.
When the switched to SAE net the power numbers decreased because now it was with the accessories mounted on the engine.
However, what they did use for a long time was SAE gross power which was engine power before the accessories such as the alternator, AC if applicable, power steering etc was added to the engine.
When the switched to SAE net the power numbers decreased because now it was with the accessories mounted on the engine.
Right on.
CF Senior Member
Joined: Feb 2006
Posts: 23,313
Likes: 25
From: Tucson Arizona
Speaking of manufacturer's horsepower ratings....I haven't been shopping for a new Rolls Royce in a year or two but I wonder if a Rolls still has officially 'un-rated' horsepower.
Years ago someone told me.....some states charge vehicle registration fees based on value, others charge by gross vehicle weight and there were a few that charged by rated horsepower. Accordingly, one of the most expensive vehicles in the world (a Rolls) paid the lowest possible registration fee due to its' official un-rated horsepower.
I imagine most states now base registration fees based on value and probably even the (new) Rolls Royce lists a horsepower rating for their motorcars.
Years ago someone told me.....some states charge vehicle registration fees based on value, others charge by gross vehicle weight and there were a few that charged by rated horsepower. Accordingly, one of the most expensive vehicles in the world (a Rolls) paid the lowest possible registration fee due to its' official un-rated horsepower.
I imagine most states now base registration fees based on value and probably even the (new) Rolls Royce lists a horsepower rating for their motorcars.