15
EXHAUST BACK PRESSURE
Keep exhaust systems to a minimum length and have
gradual bends (NOT right angle elbows). Exhaust back
pressure should be as low as possible; it is increased by
long exhaust length and sharp bends. Back pressure
should be measured with the complete exhaust system
connected and the engine running at full speed. The
correct measuring point is before the injection bend (at
the manifold flange).
Engine Exhaust Back Pressure
Beta 10 to Beta 25 70 mm Hg
Beta 30 to Beta 60 80 mm Hg
Beta 75 to Beta 105 90 mm Hg
EXHAUST HOSE
Wet exhaust hose should be matched to the injection
bend diameter. An engine correctly installed in
accordance with this handbook will meet the emission
requirements of the RCD (Recreational Craft Directive).
Engine Internal Hose Diameter
Beta 10 to Beta 60 50 mm
Beta 75 & Beta 90 60 mm
Beta 105 75 mm
There must be a propeller clearance between the tip of
the propeller blade and the underside of the hull.
This should be a minimum of 10% of the diameter of the
propeller diameter (some say 15%) to reduce ‘tip noise’.
PROPELLER CLEARANCE
19 Propeller Clearance
1640_Aug_2013.qxd:beta 1660 manual 18/11/13 10:47 Page 15
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