Mercury Racing’s new 4.6L V-8 250R and 300R FourStroke outboards are equipped with Adaptive Speed Control (ASC). This Mercury-exclusive feature allows boaters to maintain engine speed (rpm) regardless of load or condition changes – such as rough water, tight turns, tow sports and lower speeds on plane – without having to frequently adjust throttle position, a first for the outboard industry.
You may be wondering how this technology works and how to “dial in” your boat to take full advantage of the improved throttle response and “sportier” feel it provides.
While the system is designed to be intuitive to operate, understanding boat setup and operation with and without ASC will help maximize performance when changing the setup or when running the engine to its limits.
Boating Without Adaptive Speed Control
To get a boat up on plane without Adaptive Speed Control, push the throttle full forward, pulling back once on plane. Trim the engine to lift the hull, reduce drag, and increase engine rpm even with constant throttle. Heavy boats require more throttle to reach the same rpm as a lightly loaded boat.
Prop selection for this scenario is relatively straightforward. Too little pitch will result in engine revving past its recommended rpm operating range. Too much pitch will limit the engine from reaching its peak rpm for maximum speed.
250R & 300R FourStrokes
With Mercury Racing’s new V-8 FourStroke outboards, Adaptive Speed Control constantly adjusts the engine throttle and available airflow to achieve or maintain a given rpm. When the boat’s load curve is within expected limits, getting on plane no longer requires a throttle overshoot or pull-back to maintain speed.
Adjusting trim will still lift the hull and allow higher efficiency, however, engine rpm will be maintained unless helm throttle demand is increased or already at 100%.
Propping for Maximum Performance
The largest difference when propping for Adaptive Speed Control is experienced when running the engine at the top of the recommended operating rpm. For example, running a 300R with an under-pitched propeller, on a lighter than normal boat load, or over-trimmed will result with the engine reaching its maximum 6400 rpm operating range without using maximum power. In the past, the engine would continue to climb in rpm until the rev limit was reached.
With Adaptive Speed Control, the 300R Engine Control Unit (ECU) will automatically pull power to maintain the 6400 rpm limit without any indication to the driver. The only way to verify 100% power output at 6400 rpm is to have your dealer run an engine diagnostics test via the Mercury G3 tool. Any rpm less than 6400 (or max rated rpm) with the helm throttle control at full forward or 100% will result with full power output of the engine.
To ensure maximum power and performance with a 300R, we recommend working down from larger pitch propellers until you reach (6350 rpm) at 100% throttle. If the engine is under-propped or the prop leaves the water for an instant, the rev-limiter will activate to prevent engine damage.
Prop Slip and Cavitation
Common in high-performance applications, prop hub vent holes, aerators, or over-the-hub exhaust are used to allow the propeller to cavitate. Cavitation increases engine rpm, which in turn assists in getting the hull on plane. Adaptive Speed Control is not a version of traction control and thus will not reduce power or helm demand during acceleration. Under hole shot conditions, stabbing the throttle will demand 100% power from the engine and continue until the maximum 6400 rpm propping limit is reached.
Propeller cavitation during a partial helm throttle demand, i.e., while getting a up on plane, in turns or because of over-trimming is controlled differently. Where the operator used to pull back on power to prevent engine rpm from going too high, Adaptive Speed Control will reduce power to maintain the set rpm demanded by the operator. This can be experienced by entering a medium-speed turn while leaving the throttle untouched, then slowly tightening the turn until the boat slows and the propeller cavitates. Initially, Adaptive Speed Control will increase power to maintain engine rpm. When cavitation occurs, it will reduce power to maintain the same rpm.
We hope this information is helpful to you in optimizing your Mercury Racing V-8 FourStroke outboard for maximum performance.