Page 375 - REPOWER REFERENCE GUIDE (2020)

Testing the Exhaust System
• Design and size of the muffler (if applicable).
• Length of exhaust hoses.
• Amount of back pressure in the system.
The interactive nature of these factors makes it difficult to predict which exhaust system designs will be susceptible to the
tuning effect. To address this situation, Mercury MerCruiser has developed exhaust resonators that are installed aft of the
exhaust elbow outlets. The resonators help to break up the reverse pulsations, yet do not affect engine performance. In some
cases, performance increases when using the resonators.
Mercury MerCruiser recommends the use of the resonators on all models except 3.0L models that have water present after
water intrusion testing has been completed and in which the exhaust system has been confirmed to meet all specifications as
outlined in this manual. Resonators are typically more beneficial for large engines, but the kit can be used on other models as
well. The kit is available through Mercury Precision Parts and Accessories.
Resonators are installed as shown. Because of the critical nature of the placement of the resonator, Mercury MerCruiser will
free license this technology to allow the resonator to be built into your muffler. Contact your product application engineer for
details.
IMPORTANT: Complete the water intrusion test to ensure that the resonators are installed properly.
Exhaust Resonator Guidelines

NOTICE
This engine requires exhaust resonators designed specifically for this application. Failure to use the correct resonators can
introduce water to the engine, causing severe engine damage.
IMPORTANT: MerCruiser strongly recommends exhaust resonators on all models with through‑the‑transom exhaust.
On sterndrive engines using through‑the‑transom or through‑the‑hull exhaust systems, exercised special care in system design
and construction to prevent an adverse tuning effect on engine exhaust output.
• The exhaust resonator is positioned with the inside flat surface at the preferred distance of 432 mm (17 in.) from the front
edge of the exhaust hose but no closer than 51 mm (2 in.) to the exhaust outlet on the sterndrives. The 432 mm (17 in.)
dimension can be reduced, if necessary, to a minimum of 330 mm (13 in.). This dimension must be the same on both
exhaust outlets.

Typical exhaust (except 8.1L [496 cid])
f a c a - Exhaust resonator
g b - Exhaust hose
c - Dimension to inside flat surface of
resonator 33–43 mm (13–17 in.)
d - No less than 51 mm (2 in.) between
resonator and exhaust outlet or
closest fitting
b e - Hose clamp positioned around
center of resonator for retention
e f - Exhaust outlet
d g - Exhaust elbow

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Typical exhaust 8.1L (496 cid)
a c c a - Exhaust resonator
f b - Exhaust hose
g c - Dimension to inside flat surface of resonator
33–43 mm (13–17 in.)
d - No less than 51 mm (2 in.) between
resonator and exhaust outlet or closest fitting
b e - Hose clamp positioned around center of
resonator for retention
e f - Exhaust outlet
g - Exhaust elbow
d
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90-8M0149179 eng NOVEMBER 2018 © 2019 Mercury Marine Page 10B-5