Old Cars and Horsepower

[J4CKO]

Was at the Tatton Classic car show and there were a few really old cars, a lot had a number in the name that referred to the power output, i.e. whether something was a "10 Horse" or a "12 Horse", now I know that isnt BHP but whats the translation and when did BHP become the standard ?

I cant imagine any car would make do with 10 or 12 BHP, even a Fiat 500 of the old type had 19, and they barely move.

[100SRV]

If I recall correctly this "Horsepower" was derived from an RAC calculation based upon the number of cylinders and their bore.

http://en.wikipedia.org/wiki/Tax_horsepower

100SRV

[marshalla]

RAC horsepower ratings, based on piston surface area (no consideration of stroke) : http://en.wikipedia.org/wiki/Tax_horsepower

[Dr Interceptor]

I have a 1936 Vauxhall 12/6 - that's 12HP, 6-Cylinder

The engine is a 1500cc Straight Six, the actual power output will have been around 32hp.

As above, there was the RAC formula for calculating the 'taxable horsepower' which is what the cars where often named by.

[J4CKO]

Cheers !

No wonder I couldnt find a conversion with BHP.

Mystery solved.

[boyse7en]

marshalla said:

RAC horsepower ratings, based on piston surface area (no consideration of stroke) : http://en.wikipedia.org/wiki/Tax_horsepower

Hence one of the reasons why engines of that era had very small bore and long stroke. Tax dodge!