> Granted, all MG engines were overweight. How is it that small airplane
> engines can come in at about 1 hp per pound, and turn at 2500 doing it?
> Granted, they are air cooled and require oil changes at 25-30 hours, but
> 25 hrs at 60 mph on the road would be 1500 miles. Time between overhauls
> is 2000+ hours for most, again equivalent to 120,000 miles, so that's not
> a bad wear rate. How do they get that amount of power per pound at such
> low revs and normally aspirated?
> >>
> Light aircraft engines are designed to be VERY understressed because
> reliability is the main thing that the manufacturer is after. Bear in mind
> that at full throttle a light a/c engine at max rpm/ max manifold pressure is
> spinning a prop. This is much like being hooked to a dyno or a jet boat.
> Horsepower per cubic inch is usually low. A light plane with a 540 inch
> engine is making about 260 horses- not much by car standards.
> BUT----you want it to keep on making that power!
>
I think in general, there is a law of diminishing returns at work
with internal combustion engines. If you take the hp/L values of
small four-cylinders, and extrapolate to get an "estimated power" for
a 6.6L V-8, you'll discover that the larger engine should be making
somewhere in the neighborhood of 500hp or so, which most of them
don't. On the smaller scale, I've seen remote-controlled airplane
engines that put out one hp from about .25 cubic inches. How about a
10 X 10 X 10 cube of them in our MG's? 2.5L, 1000hp, and only a
slight bit of extra work synchronizing a thousand carbs!!
Scott
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