In article <3B91A0F2.C594E17A@brit.ca>, Trevor Boicey <tboicey@brit.ca>
writes
>Michael Hargreave Mawson wrote:
>> The Spitfire 1500 was advertised as the first sports car to achieve 50
>> mpg and 100 mph (although not simultaneously!).
>
> Wow that must have been a pretty feather-footed
>driver who got 50mpg. (or a 50 mile downhill and
>a generous gallon!)
Way back before official fuel consumption testing came in, the only
reputable figures came from the car magazines, who would borrow a
standard car and see what it would do. The figure of 50.6 mpg at a
steady cruising speed of 50 mph was published by "Autocar" shortly after
the 1500 was launched.
In 1977, the "Passenger Car Fuel Consumption Order" was promulgated,
and, with effect from 1st April, 1978, information from *official* tests
was available to potential buyers of new cars in the UK. The following
official figures are reproduced from the original sales literature for
the 1978 model, UK-spec, Spitfire 1500:
4-speed manual gearbox (no O/D)
Urban driving 29.4 mpg / 9.6 litres/100km
Constant speed (56mph) 50.2 mpg / 5.6l/100km
Constant speed (75mph) 32.7 mpg / 8.7l/100km
4-speed manual gearbox & O/D
Urban driving 28.7 mpg / 9.8 litres/100km
Constant speed (56mph) 52.9 mpg / 5.3l/100km
Constant speed (75mph) 36.3 mpg / 7.7l/100km
In other words, an O/D actually costs you more in fuel in urban driving
(you're not getting any benefit from it, and you are carrying extra
weight), but adds 5.4% to your fuel efficiency at 56mph, and 11% at 75.
Unless the majority of your driving is done on the motorway, an
overdrive is actually a liability!
>
> Most listers seem to get around 25mpg, however I suspect
>most listers are measuring with the slightly smaller
>US version of the gallon.
The US gallon is actually significantly smaller than the Imperial
gallon, being only 0.833 of a full gallon. That being the case, the
official figures, converted to US gallons, are as follows:
4-speed manual gearbox (no O/D)
Urban driving 24.5 mpUSg
Constant speed (56mph) 41.8 mpUSg
Constant speed (75mph) 27.2 mpUSg
4-speed manual gearbox & O/D
Urban driving 23.9 mpUSg
Constant speed (56mph) 44.1 mpUSg
Constant speed (75mph) 30.2 mpUSg
>
> Perhaps was it 40mpg? Even that sounds like a stretch
>for a real world car, but maybe one of those specially
>prepared cars with 100psi tires and a 10 speed
>gearbox. ;>
>
Even basing your calculations on the US gallon, a standard UK-spec
Spitfire 1500, straight from the factory or showroom, should give you 42
or 44 mpg on the freeway, depending on whether it has an overdrive or
not. Pump your tyres up a bit, and you might get even closer to that
magical 50 mpg!
What I have been unable to find are figures which compare the fuel
consumption of a Spit with (a) the hood down; (b) the hood up and (c)
the hard-top on. My guess is that (b) would be the most fuel-
efficient, as the drag factor is lessened, but the car is not carrying
the extra weight of the hard-top. Having said that, I beat the
official figures at 75-80mph by 22% with the top down *and* a heavy
suitcase in the car with me...
ATB
--
Mike
Michael Hargreave Mawson, author of "Eyewitness in the Crimea"
http://www.greenhillbooks.com/booksheets/eyewitness_in_the_crimea.html
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