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Originally posted by Pedr
Thanks Richard
There is a listing of "Rated Horsepower" for the 1942 Ford Flathead of 32.5, but I never understood how this figure was calculated.
Using your formula, I was able to calculate the same result for this engine.
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Good stuff!
The formula assumes a piston speed of 1000ft/sec, MEP of 90psi and mechanical efficiency of 75%. These assumptions were hugely wrong and outdated when the system started in 1920.
Incidentally the standard horsepower of 33000 ftlbs/min is wrong; James Watt measured a substantial cart horse and got 22000 ftlbs/mins but needing to promote his steam pumping engines simply added 50%. Nobody was in a position to argue in 1773 though.
This particular reference to 32hp in the Ford CMP manuals causes huge confusion on the "other side" of the Atlantic Ocean, however, remember even the army paid road tax until well into the war and since legally the tax disc has to be externally visible to the left of centre and within the front half of the vehicle, you will see the disc holder on MC's for instance, on the rear of the left bonnet (hood) vertical panel. This is often believed to be a modern addition but it is period correct.
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So I would suppose that it may have cost 32 pound/annum for road tax on a 239ci Ford flathead.
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Yes, and a huge sum then.
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And that on top of fuel expenses.  It's a good thing that times were so good in the UK post-war.
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You have us and the USA confused!! Britain was bankrupt post war; the following items were not off-ration until the dates shown, as well I remember.
July 1948 - Bread.
December 1948 - Jam.
May 1950 - Points rationing ended.
October 1952 - Tea.
February 1953 - Sweets.
April 1953 - Cream.
March 1953 - Eggs.
September 1953 - Sugar.
May 1954 - Butter, cheese, margarine and cooking fats.
June 1954 - Meat and bacon.
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Would be interesting to calculate the modern equivalent cost using the same formula at today's prices. I'd imagine that we'd all be horrified.
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Your 32hp V8 would cost the equivalent now of 5 - 6 weeks wages in tax alone. Imagine how well off the few with 50hp Rollers were. . . . . . . . . . .
This system gave us the tiny engined cars, huge taxation on fuel has kept them there and to some extent we are getting back to the RAC rating system in that road tax is now scaled on engine size and CO
2 output, the latter being another tax raiser since man's total output is a futile 0.0015% of what nature manages, and that is all generated by the sun's radiation but they can't tax that.
R.