[Seadog]

March 28 1940.
Hundred Octane
THE article Fighter Station in this issue contains a
significant reference to the use of fuel of 100
octane number by our fighters. Precise figures
for the increase in performance attained are not immediately
available, but it may be said that in an
emergency the Merlin engines as used in the Spitfires
and Hurricanes can be boosted to a pressure of I2lb.
It is also permissible to state that with its two-speed
supercharger in high gear and operating on 100-octane
fuel the Merlin R.M.2S.M. engine has a maximum output
at 16,750ft. of 1,145 h.p. The effect of the forward facing
air intake will raise considerably the height for
maximum speed.
Like other nations, America has for some time past
used iso-octane fuel in limited quantities for her military
aircraft. Lately she has adopted it as a standard,
and we may refer to the performance figures for the
Republic single-seater of the type used by the U.S. Army
Air Corps. The top speed is increased by five m.p.h.
(to 315 m.p.h.) ; the maximum rate of climb is
•3,150 ft./min. instead of 2,950 ft./min., and the ceiling
•is raised from 29,500ft. to 31,500ft. These increases do
not represent such improvements as are claimed for a
Continental machine with a Bristol Mercury XV. Using
ioo-octane fuel the top speed is 260 m.p.h. at 17,300ft.
whereas with " 8 7 " it was 236 m.p.h. at 15,700ft. The
rate of climb to 19,500ft. is reduced by four minutes.
The immense improvement in the range of the Bristol
Blenheim can be attributed directly to the use of ioooctane
fuel which permits take-off at a much higher all-up
weight. Actually the Mercury now gives 1,050 h.p. for
take-off, compared with 830 h.p.
Whatever the gains which accrue from the use of the
new fuel in our Spitfires, Hurricanes and Defiants, it is
certain that they now have an even better chance of
catching and shooting down raiders.

www.flightglobal.com/pdfarchive/view/1940/1940 - 0897.html?search=octane

and from the article Fighter Station in the same issue:

Hundred-octane fuel surges along the triple arms of a Zwicky unit into the tanks of Spitfires.
http://www.flightglobal.com/pdfarchi...?search=octane

The Bristol flew across the aerodrome full out, which led one to suggest
that, like the Spitfires' Merlins, the Mercurys were
burning 100-octane fuel. But the Spitfires overhauled it
and one by one simulated a stem attack '' opening fire
at what must have been 400 yd. range. As one pilot
broke off his attack and wheeled away another Spitfire
closed in to cover him.
In the afternoon a flight of Spitfires staged some plain
and fancy " beat-ups" of the aerodrome in formation
(excellent vie and echelon) and singly after a peel-off. This
pastime is normally frowned upon, though a certain
amount of joie de vivre is countenanced if the machines
concerned are returning from a victorious interception or
if they are demonstrating for pressmen. Here, again, the
100-octane fuel (which enables the Merlin to receive no less
than 12 lb. boost in emergency) must have been an asset.
http://www.flightglobal.com/pdfarchi...0-%200933.html