Page 52 - REPOWER REFERENCE GUIDE (2020)

Propeller Selection

• Increased load or weight (additional passengers, pulling skiers)
• A dirty boat bottom
• Operating at a higher elevation
NOTE: Additionally, high‑altitude gear sets are recommended for altitudes of 5,000 ft and higher.
The owner should be advised to recheck the WOT RPM after the first 50 hours of operation to ensure that it is still within the
specified range. By this time the engine will have completed the break‑in period. There are many variables to the "black art" of
propping. If you follow the best practices listed below, then you will be way ahead of the curve with years of enjoyable boating.
Wide‑Open Throttle ‑ RPM

It is essential for the health of the engine and overall boating enjoyment to prop a boat correctly. Not doing so will limit the boat
performance, consume more fuel, and severely shorten the useful life of the engine.
NOTE: As a boat is used it generally becomes heavier. This pulls down the engine speed. If the boat is at the bottom of the
RPM range when tested, then additional loading reduces engine speed below the recommended propping range. Continued
operation at too low of an engine speed due to overpropping will result in severe engine damage that is not covered by the
limited warranty. As a practical matter any choices made to not test and equip a boat within the recommended RPM range is a
choice to potentially forfeit limited warranty coverage.
1. Please be sure to include consideration for prop testing, changes, and gear ratio adjustments when budgeting a repower.
2. Gather information about the boat and engine: boat weight (light and heavy), boat speed, engine type, engine HP, and
number of engines.
3. Begin selection by determining the gear ratio to use in the attached charts based upon engine and boat type.
4. Select a prop by using the on‑line prop selector for Mercury and MerCruiser products, or the prop charts in this book for the
Mercury Remanufactured and Quicksilver Plus Series engines.
NOTE: The following two steps are essential for correct propping. Run the engine repeatedly at WOT for a few seconds,
even before break‑in, to verify prop selection.
5. Test the prop by running at WOT, and target the RPM in the test at the very top of the normal operating range.
6. Change prop pitch as necessary to get to a higher engine speed (RPM), if in doubt use the lower pitch prop.
The recommended WOT RPM ranges are listed in the following table.

MerCruiser, Mercury Remanufactured and Quicksilver Engine Model WOT RPM Range
3.0L, 4.3L 4V, 357 4V Alpha 4400–4800
357 MAG 4V Bravo 4400–4800
350 MAG MPI Alpha and Bravo 4600–5000
383 MAG Bravo 4V 4800–5200
383 MAG Stroker MPI, 383 MPI FWC, 385 PT Bravo 4800–5200
496 Bravo 4400–4800
496 H.O. Bravo 4600–5000
540 MAG Bravo 4V 4200–4600
540 MAG Crate Engine 4600–5000
350 and 357 Horizon Inboard 4400–4800
383 MAG Inboard 4V 4600–5000
383 MAG Stroker Inboard 4600–5000
8.1L Horizon 4200–4600
4.5L Alpha ‑ 200 4400–4800
4.5L Bravo ‑ 250 4800–5200
6.2L Bravo/Inboard/TowSport ‑ 300, 320, 350, and 370 5000–5400
8.2L MPI Inboard ‑ 375 4200–4600
8.2L MPI Inboard ‑ 425 4400–4800
8.2L MPI Bravo RPM is serial based
8.2 MAG
8.2 MAG 8.2 MAG ECT
H.O. ECT
Propeller shaft power 283 kW (380 HP) 283 kW (380 HP) 320 kW
(429 HP)

Page 4B-4 © 2019 Mercury Marine 90-8M0149179 eng NOVEMBER 2018