Exhaust System Design; Exhaust System Specifications - Mercury MerCruiser Product Applications Manual

Exhaust system tuning can be affected by various factors that are beyond the control of
Mercury MerCruiser. Following are several factors that can affect exhaust system tuning:
• Type and configuration of exhaust outlet.
• Length of exhaust hose.
• Amount of back‑pressure in exhaust system.

Exhaust System Design

Exhaust System Specifications

These engines are equipped with a wet exhaust system in which exhaust is mixed with
water in the exhaust elbows. This cools the exhaust and allows the use of heat resistant
rubber hose on the outlet side of the system. These specifications must be observed by
the OEM and muffler manufacturer when designing, manufacturing, and installing the
exhaust system:
• Exhaust elbow outlets must be a prescribed distance above the water line. Install
exhaust risers if necessary. (See Measuring Exhaust Elbow Height).
• The riser height for systems using a water lift muffler is measured to the water line in
the muffler.
MIE and V‑drive tow sport models
Tow sports inline models
• A minimum of 46 cm (18 in.) of exhaust hose must be used between the exhaust elbows
and the collector, Y‑pipe, muffler, or first angular fitting. This portion of the exhaust hose
must have a minimum of 10° downward slope. After the first 46 cm (18 in.), the exhaust
system must have a minimum of 3° downward slope. (See Measuring Exhaust Elbow
Height).
• Exhaust hoses can be installed with up to a 5° angle relative to the exhaust elbow
outlets. (See Exhaust Hose Connections).
90-863758060 AUGUST 2006
c
a
f
e
d
a - Exhaust resonator
b - Exhaust hose
c - Dimension to inside flat surface of
resonator 33‑43 cm (13‑17 in.)
d - No less than 51 mm (2 in.)
between resonator and exhaust
outlet or closest fitting
Minimum Exhaust Elbow Height
Model
b
e - Hose clamp positioned around
center of resonator for retention
f - Exhaust outlet
g - Exhaust elbow
Exhaust System
g
20458
Specification
38 cm (15 in.)
33 cm (13 in.)
Page 6A-7