Common Exhaust Pipe - Honda Motorcycle Service Manual

EXHAUST SYSTEM
On 2-stroke engines, there is the possibility that the airifuel
mixture that was scavenged just before the end of the exhaust
stroke may leak out t o some degree and be discharged into the
exhaust port.
The gas is discharged into the muffler, forming a high pressure
wave. This pressure wave impacts against the taper at the end
of the muffler, rebounds, and applies a positive pressure t o the
exhaust port. The airifuel mixture that was about t o be
discharged before the exhaust port closes is thus forced back
into the cylinder and the exhaust pulse scavenge effect is
improved.
Since the pressure wave cycle changes in accordance with the
change in engine speed, the exhaust pulse scavenge effect is
not always as effective as
it
could be at all engine speeds.
The exhaust pulse scavenge effect is regulated to a certain
range of engine speed. Therefore, the exhaust system is
designed to be most effective and most suitable for each
model, depending on its intended use.
Note that if the exhaust system is deformed due t o denting or
exhaust gas leakage, i t can effect the exhaust pulse and result
in a drop in engine horsepower.
COMMON EXHAUST PIPE
The muffler of the conventional 4-stroke multicylinder engine
uses an independent pipe for each cylinder, but most recent
models adopt a common exhaust pipe for all cylinders.
The new system features a system i n which t h e exhaust pipes
join in the exhaust chamber, and another in which the exhaust
pipes are directly joined. In both systems gas pressures ex-
hausted from individual cylinders intermingle. The pulse wave
in the muffler, generated by the staggered combustion i n ad-
joining cylinders, promotes the "pulse scavenge effect",
which increases exhaust energy absorption and reduces ex-
haust noise effectively. The resulting smaller muffler has a
decreased capacity and increased silencing capability, due t o
the reduced weight and decreased volume.
The method of exhaust pipe connection depends on the
cylinder arrangement or the required engine characteristics.
For example, an inline four cylinder engine can be connected
w i t h "4-into-I" system or "4-2-1" system etc.
AlRiFUEL MIXTURE
/
CHAMBER
4-into-I EXHAUST
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Date of Issue: March, 1 9 9 5
O
HONDA MOTOR CO..LTD