You seem to be talking about the difference between "gross" and "net"
horsepower figures. R&T test reports do not use the term "net" horsepower
(or SAE net) until around 1973. But in a 1975 Used Car Classic article
they give an "SAE net HP" of 92 for the 1962 MGB, and 98 for 1966,
although this may be an editorial oversight. But even using "net"
figures, the rating drops from 79 in 1973 to 62.5 in 1975. That seems
pretty significant.
The test acceleration results 0-60 also show a decline over the entire
period 68-77, roughly corresponding to the horsepower ratings, with a
small uptick over the last years of production, when the "net" power went
from 62.5 to 67. I posted a chart of all the R&T figures some time ago,
in a "Midget vs B" thread. My guess is that the acceleration results
curve would plot very similarly to the rated horsepower curve. Increasing
vehicle weight would account for some of the results, however.
If this discussion looks likely to continue I'll post the chart on my web
site, so everyone will have some data to chew on...
Bob Howard had this to say:
> This is one of those topics on which everyone can have a different
>opinion and still be right.
> Along the way, the procedure for HP measurment got changed. I forget
>the details, but the "new" rating is supposed to be a net rating that is
>more representative of what the engine is actually delivering. The "old"
>rating method tested the engine w/o water pump and other drags on it, and
>might have been subject to some advertising department inflation too.
> Thus the HP rating was lowered not only by a real decrease in the
>engine output, but also by making the rating more honest. The 30%
>decrease is, in all liklihood, calculated from an optimistic original
>number.
> So, with the 65 hp rating, you can be pretty sure that a typical engine
>will deliver the 65 hp, whereas with the earlier ratings the output might
>or might not be as advertised. Short of dyno testing, we will never know
>for certain.
> We have a similar issue in the TDs. The "standard" car had whatever it
>had, 56-57 HP and the MkII cars had, depending on the source of the
>information, 3 - 6 hp more. Who really knows?
>Bob
>
>
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
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