Honda G100K2 Applications Manual page 41

EXHAUST SYSTEM
EXHAUST BACKPRESSURE MEASUREMENT
Test condition
•
Full load condition
•
Oil temperature 80 – 100°C
•
Measurement time 20 s.
•
Tools: manometer with scale: mmAq or mmHg
!! In case the muffler is equipped with spark arrester,
measurement must be done with spark arrester included !!
Observe following instructions for correct measurement:
backpressure measurement test nipple location must be close to cylinder head exhaust port (see figure).
-
- on a multi-cylinder engine, backpressure measurement must be done on each individual cylinder exhaust port.
On a multi-cylinder engine, close the remaining test nipples not used for measurement. An open test nipple may
-
interfere with the backpressure measurement.
Backpressure is oscillating a lot, use a manometer with integrated filter or dampener and record the average
-
pressure reading.
Keep the measurement short in order not to damage the pressure element in the electronic manometer.
-
- If backpressure is oscillating too much and results in difficult recording with electronic manometer, use a tube
with watercolumn.
VALVE TIMING – EXHAUST BACKPRESSURE
A high–performance spark ignition engine with great valve
overlap takes full advantage of the pulse effects in the
intake and exhaust manifold.
The idling and partially open throttle operation suffers since
the reduced induction manifold pressure and gas flow
causes back-flow of the exhaust.
Furthermore, full load fuel economy is poor since some
unburned mixture will pass straight through the cylinder
when both valves are open at Top Dead Center.
The level of exhaust residuals trapped in the cylinder has a
significant effect on the cycle-by-cycle variations in
combustion and the emissions of Nox.
As with exhaust gas recirculation, high levels of exhaust
residuals lead to lower emissions of Nox and greater cycle-
by-cycle variations in combustion.
The level of residuals increases with:
•
Decreasing absolute inlet manifold pressure
•
Reduced compression ratio
•
Increased valve overlap
•
Decreasing speed
•
Increasing exhaust backpressure
In engines with valve overlap (e.g. GX610/620), correct
exhaust back pressure is important for good engine
operation.
Cylinder head exhaust port
- 40 -
Test nipple
Inside diameter 4mm
Tube length > 150mm
Exhaust pipe