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 -1995
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.
Both the 3 inch and 4 inch
risers have drilled and
tapped bosses to install
the shift bracket (left) and
the ignition module (right).
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  
Cast Iron                  # 51110                  $99.95

Aluminum                # 51115                $149.95
_______________________________________  
Mercruiser 4 Inch Exhaust Riser   
Cast iron                 # 51140                   $99.95
 
Aluminum               # 51145                 $149.95
MerCruiser Engines may come with either a 3"
riser or a 4" riser.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
Both the 3-inch and the
4-inch risers have the
same mounting flange
dimensions.