Re: [FWDLK] Factory Horsepower Ratings

[Bill Watson <wwatson6@xxxxxxx>]

AMA (Automobile Manufacturers Association, and its predecessors - National
Automobile Chambe of Commerce, Association of Licensed Automobile
Manufacturers) horsepower, or RAC (Royal Automobile Club) or taxable
horsepower.

The system basically took into consideration the bore of the engine and the
number of cylinders.  When this horsepower rating was devised, back before
WWI, it was a fairly accurate method of comparing engines for power.
Compression ratios were about 4:1 and the generally the bigger the cars, the
bigger the bore, 5 4, 6, 8, etc. engine cylinder sizes.

The formula looked like  (D x D) x N, all divided by 2.5, where "D" is the
bore of the engine and "N" the number of cylinders.

Thus an engine with a 3" bore would be rated at 14.4 hp for four cylinders,
21.6 hp for six, 28.8 for eight and 43.2 for twelve cylinders.  Compare the
following 1915 cars -

Saxon 4  - 96" wheelbase - 2.75" bore  - 12.10 hp
Maxwell 4 - 103" wheelbase - 3.625" bore - 21.03 hp
Dodge Brothers 4 - 110" wheelbase - 3.875" bore - 24.03 hp
Chalmers 6 - 124" wheelbase - 3.124" bore - 23.44 hp
Packard V12 - 135" wheelbase - 3.00" bore - 43.20 hp
Locomobile 6 - 143" wheelbase - 4.50" bore - 48.60 hp
Pierce-Arrow 6 - 147.5" wheelbase - 5.00" bore - 60.00 hp

Many states and provinces charged an annual tax on a car, and used the
AMA/NACC/ALAM horsepower classifications.  And it survived into the 1950's.
Of  course by the 1930's with the arrival of tetraethyl lead compression
ratios began to increase, and along with 2-barrel carburetors supercharging,
brake horsepower began to increase making the system a little out of date.
Instead of horsepower, weight or size became the basis of annual taxes/fees.

Bill
Vancouver, BC


----- Original Message ----- 
From: "Jan & Roger van Hoy" <vanhilla@xxxxxxxxxxxx>
To: <L-FORWARDLOOK@xxxxxxxxxxxxx>
Sent: Friday, November 02, 2007 5:45 PM
Subject: Re: [FWDLK] Factory Horsepower Ratings


> That's probably AMA horsepower, not brake horsepower.
>
> Don't ask me to explain that rating...
>
> --Roger van Hoy, Washougal, WA, '55 DeSoto, '58 DeSoto, '56 Plymouth, '66
> Plymouth, '41 Dodge
>
>
> ----- Original Message ----- 
> From: "Paul Holmgren" <PAULHOLM@xxxxxxxxxxxxx>
> To: <L-FORWARDLOOK@xxxxxxxxxxxxx>
> Sent: Friday, November 02, 2007 1:34 PM
> Subject: Re: [FWDLK] Factory Horsepower Ratings
>
>
> > To add to the 'fun' concerning horsepower ratings, all one has to
> > do is peek at the 'reported' figures in any period (50's-60's)
> > Motors repair manuals.
> >
> > Their quoted HP figures for the Chrysler cars was something like
> > 54 for the windser up to the 300, they all had the same figure in
> > that column as I recall seeing once.
> >

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