Deagostini RB7 - The GX21 Silencer System; The GX21 Silencer System Components

Red Bull Racing RB7: Step by Step
™
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THE GX21 SILENCER
SYSTEM
UNLIKE THE SILENCER SYSTEM OF A FOUR-STROKE ENGINE, THAT OF A TWO-
STROKE NOT ONLY EXPELS THE EXHAUST GASES AND REDUCES THE NOISE, BUT
ALSO HELPS COMPRESS THE FUEL-AIR MIXTURE IN THE COMBUSTION CHAMBER.
On a four-stroke engine, expelling the exhaust gases and
reducing noise are the main tasks of the silencer system,
but the silencer of a two-stroke – such as your GX21 – is
used primarily to optimise its performance.
With a four-stroke, the inlet and exhaust ports of the
combustion chamber are opened and closed by valves.
When the piston moves downwards on the rst (induction)
stroke, the inlet valve opens and the fuel-air mixture ows
into the combustion chamber. After the compression and
combustion strokes comes the exhaust stroke, when the
exhaust valve opens and the piston drives the exhaust
gases out of the chamber.
The situation is dierent with the two-stroke engine,
where it is the movement of the piston that opens or
closes the inlet and exhaust ports (see the intro section in
Pack 16). When the piston is at the top of the combustion
chamber, it is closing o both the inlet and the exhaust
ports. As it moves downwards on the combustion stroke, it
opens the exhaust port and the exhaust gases are ejected
by the pressure generated by the explosion. As the piston
moves further downwards, it also opens the inlet port,
while suction is created in the combustion chamber by the
escaping exhaust gases. Since both ports are open and the
piston is at the bottom of the cylinder, the fuel mixture is
drawn not only into the combustion chamber but also into
the silencer system. This is a really undesirable eect, since
it means that a portion of the fuel-air mixture can escape
unused and is wasted.
Dome-headed screws
O-ring
O-ring
Silencer cap
Silencer (expansion chamber) assembly
Manifold
Tailpipe
The GX21 silencer system
components
Dome-headed screw