An article from the Sydney Morning Herald comments on this years racing cars 1906 and notes the 6 cylinder Napier car.

Sydney Morning Herald (NSW, Australia)
19 April 1906
Page 10

THIS YEAR’S RACING MOTOR CARS.

According to the latest files to hand, this year’s
racing motor cars will present fewer novelties than
ever before. Transmission by propeller-shaft is gain-
ing in favour every day over chain drive, and all the
machines are being built with their centre of gravity
placed very low. One peculiarity which the new regu-
lations at home have engendered is that all cars will
have a large fuel capacity, provision being made for
as much as 45 gallons of petrol, and a proportionately
large oil supply, in order to cover the six rounds of
the circuit without stopping to fill tanks. Excepting
the Mercedes, and of course the six-cylinder Napier, it
is probable that all the starters will have four-cylinder
engines. The Richard Brasier cars, with four cylinders
of 165-m.m. bore, and 104 h.p., will have transmission
by cardon shaft. The Mercedes six-cylinder have 150-
m.m. bore, and 140-m.m. stroke, giving 135 h.p., four
speeds, with direct drive on the high, and ball bear-
ings throughout. Several of the French drivers have
already made acquaintance with the circuit, Hemery
visiting it on a 1905 racer immediately before his
triumphal return from Florida.

Reference: http://trove.nla.gov.au/newspaper/article/14766140

Another Napier Speed Record at Brooklands is mentioned in this article from The Advertiser in August 1908.

The Advertiser (Adelaide, S.A., Australia)
5th August 1908
Page 8

DEMON MOTORING.

A THIRTY-MILE RECORD.
LONDON, August 3.

A 60-horsepower Napier motor car won
the 30-mile race on the Brooklands track
on Saturday at a speed of 101 miles an
hour. A new record was created. A Mer-
cedes car of 75 horsepower was beaten by
only 60 yards. Although the speed of the
Napier car is a record for 30 miles, it is
not the highest yet produced, Nazzarro, the
“Demon motorist,” having on June 8 on the
same track covered three miles at 111 miles
an hour. At times he travelled much
faster. On other tracks even greater speeds
have been attained.
To judge from the speed of 121.6 miles an
hour, reached by Mr. A. Lee Guinness dur-
ing the recent, motor car trials on Salt-
burn Sands, this course is little Iess speedy
than the world-famous beach track on the
east coast of Florida, on which so many
sensational speed feats have been per-
formed. It was on this course, which
runs for 100 miles by the side of the sea
and is almost as hard and smooth as a
billiard table, that Mr. W. K. Vanderbilt.
jun., covered, in January, 1904, a rale in
39 sec. (over 92 miles an hour). Since
this feat, which was considered phenomenal
at the time, records have had a bad time
in Florida. A year later, on January 30,
1905, Mr. Arthur Macdonald travelled a
mile in 34 2-5 sec., more than 104 miles
an hour. In the following January Mr.
Stanley, on a steam car, brought the time
down to 31 4-5 sec.; and three days later,
a speed of two miles a minute was exceeded
for the first time, when Mr. Marriott, on
a Darracq car, placed the record at the
starting figure 28 1-5 sec., representing a
speed of 127 2-3 miles an hour.

Reference: http://trove.nla.gov.au/newspaper/article/5169435