Horse Power Ratings - comparison

[JRA]

I was comparing the horse rating of my cars, and got very confused with the information, because seems there are different ratings for the same car. Anyway, most the information I was able to collect seemed to be coherent, for example: 1928 Ford (28HP); 1928 Chevrolet (35HP); 1929 Plymouth (45HP); 1929 Dodge-Brothers (63HP) apparently makes sense. For large engines, as 1929 Chrysler (75HP); 1929 Hudson (92HP); 1927 LaSalle (75HP); 1926 Studebaker (75HP); 1929 Marmon (86HP), the information seemed to be reasonable. However, for the 1927 Franklin (32HP) data surprised me. Am I comparing apples to oranges here ??

[rocketraider]

Are these figures brake horsepower or taxable horsepower?

[Fordy]

I have an Engish Ford Prefect -10hp taxable. Not sure what the actual figure is but at least 9 of those taxable ones are in pet food now.

[JRA]

Brake horse power, as far I understand.

[nearchoclatetown]

Early cars used a formula using bore and stroke. Had nothing to do with horses. 

[nzcarnerd]

Worth a read - Tax horsepower - Wikipedia

[wayne sheldon]

There are at least a dozen different ways to rate "horsepower". A few are legally codified (legally defined), others scientifically or mathematically defined. Some are test results. Some amount to total power consumed or produced while others eliminate wasted power, which may or may not include drive train resistance. "Taxable" horse power is used around much of the world, and is generally a simple formula involving little more than the cylinder displacement which in turn determines the annual vehicle tax. But not used in the USA, which is why US automobiles have historically had big engines.

 

Just a basic background for my Brazilian friend.

[nzcarnerd]

8 hours ago, wayne sheldon said:

There are at least a dozen different ways to rate "horsepower". A few are legally codified (legally defined), others scientifically or mathematically defined. Some are test results. Some amount to total power consumed or produced while others eliminate wasted power, which may or may not include drive train resistance. "Taxable" horse power is used around much of the world, and is generally a simple formula involving little more than the cylinder displacement which in turn determines the annual vehicle tax. But not used in the USA, which is why US automobiles have historically had big engines.

 

Just a basic background for my Brazilian friend.

The horsepower formula of D squared times N divided by 2.5 must have been used at one time in the US as my copy of the Floyd Clymer Catalog of 1914 cars - essentially a reprint of the NACC catalog of the time has a copy of the chart with the horsepower figures for the various bore sizes. It says it was previously known as the ALAM rating and is "based on the average view of eminent engineers as to a fair conservative rating for a four-cycle motor at one thousand feet per minute piston speed".

[AzBob]

 

7 hours ago, nzcarnerd said:

The horsepower formula of D squared times N divided by 2.5 must have been used at one time in the US as my copy of the Floyd Clymer Catalog of 1914 cars - essentially a reprint of the NACC catalog of the time has a copy of the chart with the horsepower figures for the various bore sizes. It says it was previously known as the ALAM rating and is "based on the average view of eminent engineers as to a fair conservative rating for a four-cycle motor at one thousand feet per minute piston speed".

X2.

To add to nzcarnerd's post, Ford used S.A.E. horsepower rating of 24.03 in the specifications page of the Model A Instruction Book. The brake horsepower was closer to 40. The calculated horsepower rating was used at some point in the U.S. Thanks to nzcarnerd's link to Tax horsepower, apparently Missouri still uses taxable horsepower charts.

 

Below from Instruction No. 83 of Dyke's Automobile and Gasoline Engine Encyclopedia (1931)

 

"N.A.C.C. formula is used by all leading manufacturers and by the license offices in different cities. It represents a comparative horsepower rating for automobiles that is used for taxation and similar purposes."

 

 

Edited April 9 by AzBob (see edit history)