Page 11 - The Origin of the Species

THE ORIGIN OF THE SPECIES 11
alloy oil cooler and filter unit was also fitted, along with a new alloy radiator for
enhanced cooling. Larger twin SU H6 carburettors, oversized inlet and exhaust
valves, a forged steel high-lift camshaft, and an 8.3:1 compression ratio that
helped increase output by almost 50 percent over the standard 100 engine for a
total of 132 bhp at 4700 rpm and 168 pound-feet of torque at 2500 rpm, allowing
the car to reach 120 mph and accelerate from 0 to 60 mph in 7.8 seconds.7
With the liberal use of lightened alloy components in conjunction with the
aluminum external panels and internal substructure, the new vehicles were some
220 pounds lighter than the standard 100 production cars. The most significant
alteration, apart from the more powerful engine, was the installation of Dunlop’s
proprietary disc brakes, which had been created for use in Jaguar’s sports racers.
Fitted with four-piston calipers and 11.5-inch rotors, the brakes operated through
a Plessey hydraulic pump driven from the rear of the gearbox. To increase top
speeds and provide more clearance for the untried disc brakes, the 15-inch wire
wheels were replaced with 16-inch Dunlop center-lock magnesium alloy wheels.
(LEFT) The improved
engines used in the second
tranche of Special Test Cars
and later adopted for use in
the 100S featured a Weslake-
designed cylinder head that
placed the carburettors on the
opposite side from the layout
used in the standard 100
and 100M. (The Donald Healey
Collection)
(BOTTOM LEFT) With a
number of special components
and a higher compression
ratio, the uprated units
installed in the later Special
Test Cars and retrofitted into
the earlier examples and the
production 100S produced
132 bhp at 4,700 rpm and
160 pound-feet of torque at
2,500 rpm. (The Donald Healey
Collection)
(BOTTOM RIGHT) The
most impressive components
that the Special Test Cars
would adopt were the Dunlop
disc brakes that had first
appeared on the Jaguar C
and D-types that competed
at Le Mans. (The Donald Healey
Collection)