Four inch riser elbow cutaway view
three inch riser cutaway
Mercruiser 4 inch
riser (accepts a 4
inch exhaust
hose).  This riser
is used on 1987 -
2002 MerCruiser
V6 and V8 engines
with the center
riser manifolds.  
Mercruiser 3-inch
riser, (accepts a
3-inch exhaust
hose).  This riser
is used on 1983
-1986 MerCruiser
V6 and V8 engines
with the center
riser manifolds.  
A cutaway view shows the internal difference between the 3 inch riser
(left) and the 4 inch riser (right).  The 3 inch riser accepts a 3 inch
inside diameter rubber exhaust hose.  The 4 inch riser accepts a 4
inch inside diameter rubber exhaust hose.  The inside diameter of the
exhaust outlet is 2 3/16 inches for the 3 inch riser and 2 1/4 inches for
the 4 inch riser. There is a performance increase when switching from
the 3 inch to the 4 inch because of the smoother radius of the exhaust
path in the 4 inch riser.  
External height is exactly 6 3/4 inches for both risers.  Angle of the
exhaust outlet for the 3 inch riser is 15 degrees down.  Angle of the
exhaust outlet for the 4 inch riser is 7 degrees down.
View of ignition module mounted on the riser
View of shift bracket mounted on riser
Both the 3-inch and
4-inch risers have
drilled and tapped
bosses to install the
shift bracket (left)
and the ignition
module (right).
riser attaching studs
The 3 inch riser is attached with short studs (included).  
The 4 inch riser is attached with 6 inch long bolts (included).
Mercruiser 3 Inch Exhaust Riser  #51110
$99.95

Mercruiser 4 Inch Exhaust Riser  #51140
$99.95  
MerCruiser Engines may come with either
a 3" riser or a 4" riser.
Replaces:
3-inch riser Merc. 98504A3
4-inch riser Merc. 807988A03
The size of the riser is determined by the
diameter of the hose that connects the riser to
the exhaust pipe.  
A 3" hose or a 4" hose.
Mercruiser Risers/Elbows
riser attaching bolts
Riser attaching bolts on riser
Riser flange dimension
Four inch riser hose dimension
Three inch riser elbow hose dimension
Three inch riser side view
Three inch riser diagonal view
Comparison between 3 and 4-inch risers
Both the 3-inch and the
4-inch risers have the
same mounting flange
dimensions.