Mercruiser Exhaust Systems and Accessories
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THROUGH THE TRANSOM OR HULL EXHAUST
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NOTICE |
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Refer to Exhaust Resonators in this SECTION for additional information on 454 and502 cid (7.4 L and 8.2 L) engine exhaust requirements. |
When designing and installing an exhaust system, in addition to other model specific requirements, Mercury MerCruiser requires the following to be observed:
- Exhaust fittings (flanges and outlets) must be of proper size to accommodate 4 in.(102 mm) inner diameter exhaust hoses.
- Exhaust fittings must be equipped with internal water shutters.•An exhaust flapper must be used over each outlet.
- Exhaust outlet must be slightly above the water line with boat at rest in the water and a full load aboard.
- Exhaust hoses, collectors and pipes must not be higher than exhaust elbows at any point.•The drop in the exhaust system must be continuously sloping so that a low spot does not exist at any point in the exhaust hose or pipe.
- The exhaust system on Mercury MerCruiser engines must have a minimum of 6°downward slope between the exhaust elbow outlet and the exhaust outlet of the boat.•The exhaust system on Mercury MerCruiser engines must have a minimum of 4 in.(102 mm) of vertical drop between the exhaust elbow outlet and the exhaust outlet of the boat.
EXHAUST RESONATOR
The exhaust resonators (provided with the engine package or available separately) aredesigned to provide increased resistance to water ingestion due to the tuning effects of the exhaust system. Quicksilver resonators are designed to break up the exhaust pulses.
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CAUTION! |
| Avoid severe engine damage. Water ingestion by the 454 and 502 cid (7.4Land 8.2L) engines may occur in some instances without the use of speciallydesigned exhaust resonators. Install exhaust resonators in the exhaust system when specified. |
IMPORTANT: Exhaust resonators must be installed on 7.4L MPI, 454 Mag MPI and 502Mag MPI Models of sterndrive engines with through the transom (or through the hull) exhaust
On 454 and 502 cid (7.4 and 8.2L) sterndrive engines using through the transom or hullexhaust systems, special care must be exercised in system design and construction toprevent an adverse tuning effect on engine exhaust output.
Exhaust system tuning can be affected by various factors that are beyond the control ofMercury 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 Resonator Kit use on Sterndrive Models:
| CAN Be Used With | CANNOT Be Used With |
| 1. Transom mounted muffler tips.
2. Waterlift mufflers or other mufflers that are mounted outboard of exhaust elbows. 3. Open exhaust. |
1. Silent Choice Exhaust System.
2. Below swim platform exhaust. 3. Mufflers that mount between exhaust elbow and exhaust tip. |
INSTALLATION
The resonator is installed in exhaust hose with open end toward exhaust elbow. Resonatoris positioned so that inside flat surface is approximately 17 in. (432 mm) from front edgeof exhaust hose, but no closer than 2 in. (51 mm) to exhaust outlet on sterndrive. The17 in. (432 mm) dimension can be reduced, if necessary, to a minimum of no less than13 in. (330 mm).
A clamp is then installed and tightened around the hose so that it clamps around center ofresonator. This position is 1 in. (25 mm) less than the position of the resonator as discussedin the previous paragraph.
454 AND 502 MAG BRAVO MODEL EXHAUST RECOMMENDATION
IMPORTANT: To get maximum performance from Magnum Bravo Models, through the transom or hull exhaust is required.
NOTE: If noise regulations do not allow the use of through the transom or hull exhaust, an exhaust pipe kit (Quicksilver Part Number 44266A6) must be installed for through the prop exhaust. This kit also contains an exhaust tube that is used in place of the exhaust bellows.
IMPORTANT: It is recommended that the exhaust bellows on the transom assembly be removed. This is necessary to avoid creating a vacuum at the exhaust outlet in the propeller at higher boat speeds. This vacuum could degrade propeller performance on some boats.