The Brooklands
Silencer (known in 1927 as The Brooklands "Official
Receiver")
(Reprinted with
appreciation from 'Speed and How to Obtain
It', by J. E. G. Harwood, B.A. (Oxon.) 2nd
Edition, 1927)
Chapter XV -
Tuning
"
The rules
concerning the "Official Receiver" are as follows .
. 1. An ordinary touring car or motorcycle must be
fitted with an ordinary touring silencer if and
when used on the track for private and touring
purposes, as distinct from competitions. 2. Except
as above mentioned, all cars and motor cycles when
running on the track shall be fitted with the type
of silencer hereinafter described.
3. Construction
(a) A pipe from
the exhaust valve or valves shall be led into a
receiver, which shall be situated as close as
possible to the engine.
(b) This pipe
shall penetrate into the receiver to a distance of
2 inches and no more.
(c) The capacity
of the receiver mentioned in paragraph (a) shall
not be less than six times the volume swept by the
pistons of one cylinder of the engine, and such
receiver if cylindrical shall not be of greater
length than four times its maximum diameter, and be
of irregular shape of equivalent proportions. The
top, bottom and ends of the receiver, in side
elevation, shall be straight lines and shall be
parallel to one another respectively. The ends
shall not be at an angle of less than 45 degrees to
the top and bottom lines of the receiver. In
addition the extensions of the bottom and inlet
pipes into the receiver must be parallel to one
another and to the top and bottom of the
receiver.
(d) An exit pipe
shall lead from this cylinder as far as the back
axle. This exit pipe shall protrude into the
receiver specified in paragraph (a) to a depth of
two inches, and no part of this exit pipe shall be
of greater cross-sectional area than the minimum
area of the exhaust port of any one cylinder.
(e) The pipes
leading into and out of the receiver shall not be
opposite each other in the receiver, but shall be
out of line to the extent of one and a half inches
measured at points on the circumference, and not
between pipe centres, so that if the pipes were
continued there would be a space between the pipes
at a place where they overlapped sufficient to
allow of the passage of a one and a half inch
gauge.
(f) No device may
be employed in the receiver which would tend to
produce a straight through flow of the exhaust
gases between the inlet and outlet pipes.
(g) The exhaust
gases must not pass direct from the exit pipe to
the atmosphere, but must be finally emitted from
what is commonly known as a "fish tail" on the end
of the exit pipe. The orifice of such "fish tail"
shall be approximately rectangular in shape, and of
the following dimensions -
For
engines with a capacity up to and including two
litres
small dimension, not more than one
quarter inch
large dimension, not more
than six inches.
For engines
with a capacity over two litres . . . small
dimension, not more than one half inch . . .
large dimension, not less than twelve inches.
The length of the
fish tail when fitted shall be measured from the
end of the exit pipe to a point situated at the
centre of the orifice, and the length of the fish
tail shall be equal to the larger diameter of the
orifice. Thus, if the orifice of the fish tail is 9
inches by 1/4 inch the distance from the end of the
exit pipe (where the tail commences) to the centre
of the orifice shall be 9 inches. The surface of
the fish tail shall be flattened as far as
possible, and shall taper from the end of the exit
pipe to the orifice. (h) The after half of the
sides of the fish tail, that is to say, the half of
the fish tail nearest the orifice, may be
perforated with holes not greater than 3-32nds in
diameter. The number of holes is not limited.
4. In spite of
the fact that a competitor may have complied with
the above regulations the Brooklands Automobile
Racing Club, through its official or duly appointed
representative, shall have the right at any time
exclude any vehicle from the track or grounds
within its jurisdiction if, in the opinion of such
official or representative, such vehicle has made
or might make undue noise.
5. If while any
vehicle is using the track during the progress of a
race, record breaking attempt or test, or for any
purpose whatever, its silencer should become
detached, deranged or broken in such a manner as to
allow of the emission of the exhaust gases through
any other place than the orifice of the fish tail,
such vehicle shall if competing in ally race,
record breaking attempt or test, be liable from
that moment to be disqualified from taking any
further part in any such event, and shall in any
case throttle down and leave the track
forthwith.
6. The Brooklands
Automobile Racing Club, by its official or duly
appointed representative, reserves the right to
examine the interior of any silencing apparatus
fitted on competing vehicles, and may disqualify
any competitor whose apparatus in the opinion of
such official or representative does not comply
with these regulations, and may withhold, withdraw
or deal with, as it thinks fit, any prize,
certificate or other award to which such competitor
would otherwise have become entitled as a result of
the use of the offending vehicle".
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