Max,
Yes, it is partly the difference between gross and net hp, and there is
no intention to say that true horsepower did not decrease over the years.
Nobody who has not put each type of engine on a dyno can say for certain
what the HP output really was. Many suspect that the "gross" ratings were
inflated, or perhaps specially prepared engines were tested. We'll never
know for sure.
Anyone with a stopwatch can measure the effect of reduced power, which
is what the magazines did, and they clearly tracked the acceleration
deterioration.
It would be interesting to speculate how much weight would need to be
removed from an MGB to allow the 1975 car to accelerate as briskly as the
1966 model.
Bob
On Sat, 17 Jun 2000 08:41:05 -0700 Max Heim <mvheim@studiolimage.com>
writes:
> 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.
>
|