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Here's an easy way to get into small-bore
Modified racing
BY WALLY KORB
WHEN JERRY TITUS ROAD TESTED THE SUNBEAM IMP IN SCG,
AUGUST 1964, he praised the power plant as being "literally a gift from the
Gods for Class G and H special builders." And the specifications listed
told why - weight of complete power train of 180 pounds, eight-port light alloy
head, single overhead cam design, plus a very sturdy bottom end that could take
considerable power increase over the stock 42 bhp.
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Driver/ owner Fred Minning is shown at left aboard the tiny machine. |
One of the people who listened and believed was Fred
Minning of Melbourne, Florida, who campaigned an Imp Special last year rather
successfully. The car was no beauty winner, but under its homely little hide
beat a healthy engine, and the car frequently surprised some good HM
competitors.
Meanwhile, Gene Beach of Clearwater, Florida,
co-designer of the very successful Begras (see SCG, November 1962) and the Beach
Formula Vee, had been polishing up some more ideas for a small Modified design,
and Fred decided the best way to improve on chassis and body design for his new
car would be to work with Gene. Their work has produced three cars, one owned by
Fred Cox and driven very successfully at recent Daytona Nationals, and another
driven by Fred at the same races.
Basically both cars are much the same, although the Cox machine had a much more highly modified engine, and was considerably faster than Minning's. Fred estimated his engine was developing 65 bhp, and felt that Cox's car was probably putting out a solid 80 bhp, which is his goal for state of tune by November 27-28 when the American Road Race of Champions gets under way at Daytona Speedway.
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To the basic Sunbeam Imp engine, Minning opened up
the clearances on rod and main bearings 0.001 and piston clearances by 0.006.
Then he destroked it by 0.080 and milled the head 0.040 to bring the compression
ratio back to standard 10.0 to 1. This brought the displacement to about 747
cc's, but left undone much in the way of increasing valve size and cam
configuration, two things which will definitely be done before the car is raced
again. Unfortunately, oversized valves and seats are not obtainable in this
country, and although Sunbeam is most cooperative about helping special builders
in modifying the Imp engine, these parts are simply not readily available.
The chassis is largely what Beach calls his Mk. 4B,
light yet strong enough to move up to as large as F Modified power with only a
few enlargements made to the engine bay section. Front suspension is of
fabricated unequal A-arms, with Triumph Herald spindles and disc brakes with
Airheart calipers. The rear suspension uses a cast magnesium hub carrier of
Beach design and manufacture, with Sunbeam Imp stub axles and hubs, which are
quite strong and light. There are unequal A-arms with two trailing arms for
positive location, and once again, Triumph Herald discs with Airheart calipers
are used for braking.
The very popular Fiat transmission was used on this car, although Fred hopes to use an Imp five-speed later on, when more money is available. Consequently, Fiat half-axles had to be mated to the Imp stub axles, and a bell housing was carefully fabricated, although Gene Beach hopes to manufacture a magnesium one some time in the near future. The clutch is a League of Nations variety, with a Fiat Abarth competition driven disc, a Triumph Spitfire competition pressure plate, all being used with the Imp flywheel.
 The nose-mounted radiator is a fabricated cross-flow job. |
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Cooling is provided by a special crossflow radiator
which Beach has made up for him, and all piping is run down the right side
because of engine configuration and water pump location. Since the engine is
mounted very low in the chassis, a BMC oil cooler was added to keep oil
temperature down to about 190 degrees. Because of its very low location, the
engine uses a very flat oil pan which is carefully baffled. This, in connection
with the oil cooler, seems to have the oil temperature problem pretty well
solved.
Although the car has never actually been weighed,
careful addition of components and liquids places the ready-to-run weight at
just under 700 pounds. With a solid 80 horsepower on top, and plenty of revs
available in the intermediate gears, these specials will be able to give the
best of H Modified a good run for the checkered flag.
Information on the Mk. 4B is available from Gene
Beach at Competition Components, Inc., 2032 Gentry Street, Clearwater, Florida.
