MANIFOLDS, ELBOWS AND RISERS
SERVICE MANUAL NUMBER 22
90-860074--1 FEBRUARY 2002 Page 7B-9
Locating And Installing The Inboard (MIE) Exhaust System
IMPORTANT: It is the responsibility of the boat manufacturer, or installing dealer, to
properly locate the engine and install the exhaust system. Improper installation may
allow water to enter the exhaust manifolds and combustion chambers and severely
damage the engine. Damage caused by water in the engine will not be covered by
Mercury MerCruiser Warranty, unless this damage is the result of defective part(s).
Determine if an exhaust riser kit or a water lift muffler kit is required, by taking measurements
“a” and “b”, with boat at rest in the water and maximum load aboard. Subtract “b” from
“a” to find “c”. If “c” is less than specified in chart, an exhaust riser kit or a water lift muffler
kit must be installed.
Model
“c” = “a” Minus “b”
All Models “c” Must Be 279 mm (11 in.) or More
73592
c
a
b
c
d
Typical Inboard (MIE) Engine
a - From Waterline To Top Of Transom
b - From Highest Point On Exhaust Elbow To Top Of Transom
c - From “a” minus “b”
d - Waterline At Rest
Additional information:
1. If an exhaust riser or a water lift muffler kit is NOT required:
• The exhaust outlet (for routing exhaust to outside of boat) must be located so that a mini-
mum of 13 mm (1/2 in.) per 305 mm (12 in.) downward pitch (drop) exists in the exhaust
hose or pipe from the engine exhaust elbow to the outlet.
• A minimum drop of 100 mm (4 in.) overall is required. (This is an American Boat and
Yacht Council recommendation.) The drop must be constant so that a low spot does not
exist at any point in the exhaust hose or pipe.
2. Exhaust outlet must be slightly above the water line with boat at rest in the water and
a full load aboard.
3. Exhaust outlet should be equipped with an internal shutter to prevent seawater from
running back into exhaust system.
4. The use of an exhaust flapper on each outlet also is recommended.
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