Choosing the right stator system is critical when working on or upgrading a Mercury 2-stroke V6 outboard. From the early 2.0-liter engines to the powerful 2.5-liter racing variants, these motors rely on properly matched ignition and charging components to perform reliably at high RPM or under extended load. Among the most important components is the stator, which is responsible for both ignition power and battery charging.

Mercury V6 outboards primarily used three stator configurations: 9-amp, 16-amp, and 40-amp systems. While 40-amp setups were common on stock 2.4L models from 1989 and widely used in 2.5L production engines between 1991 and 1999 (including XR6 models), performance builds often utilize lighter 9-amp or 16-amp stators for racing or hybrid recreational applications.

Understanding the differences between these systems—and their compatibility with flywheels and electrical loads—is essential for a successful build or repair.

Mercury V6 Outboard Platforms: 2.0L, 2.4L, and 2.5L

The Mercury 2.0L V6 was one of the earliest versions in this family. Compact and relatively simple, it served as a foundation for many of Mercury’s CDI innovations in 9 and 16-amp ignition and charging systems. These engines were often used in lightweight hulls and racing applications.

The 2.4L V6 became the standard through the mid to late 1980s, powering models like the Bridgeport and many carbureted or EFI outboards. Both stock and race 2.4 Liters were equipped with 9 and 16-amp ignition and charging systems. Starting around 1989, stock 2.4L engines began using 40-amp stator systems to support growing electrical demands. These heavier-duty systems continued into the next generation.

By 1991, Mercury had introduced the 2.5L block, which became the backbone of their performance and recreational lines for the next two decades. Many stock 2.5L models built between 1991 and 1999—such as the XR6, 200 EFI, and others—used 40-amp stators from the factory.

Meanwhile, high-performance versions of the 2.5L, like the 260, 280, and 300 Drag, used lightweight flywheels and smaller 9- or 16-amp stators to reduce rotational mass and improve throttle response.

What Does the Stator Do?

The stator is a fixed coil mounted under the flywheel. As the flywheel spins, magnets embedded in the flywheel pass over the stator windings and generate alternating current (AC). This current powers two critical systems: ignition and battery charging.

For ignition, the stator supplies power to switch boxes or CDI modules, which then fire the spark plugs. For charging, it sends current to the rectifier or voltage regulator, which converts the AC power into usable DC current for the battery and electrical accessories.

In Mercury outboards, stators are identified by their current output: 9 amps, 16 amps, or 40 amps. Each type has specific applications, performance characteristics, and flywheel compatibility.

The 9-Amp Stator

The 9-amp stator was designed with one purpose in mind—maximum performance in short bursts. This system produces around 9 amps of power, just enough to support ignition and provide a light trickle charge to the battery. It was used in early high-performance V6 outboards, and racers also install them on Mercury Racing 2.5s like the 260 and 300 Drags, where throttle response and top-end power take priority over charging capacity.

Because it generates less magnetic drag and less charging current, the 9-amp stator runs cooler and can be paired with very lightweight aluminum or steel flywheels built specifically for low-output systems. These combinations are ideal for drag racing and short high-RPM runs where minimal rotational mass is a benefit.

However, the system is not designed to power accessories like GPS units, aerators, or running lights, and extended idling or long trips can quickly drain the battery.

If you're running a race boat or a stripped-down performance hull with no electrical accessories, a 9-amp stator may be the best option—just be aware of its limitations in real-world use.

The 16-Amp Stator

For applications that require more electrical output without sacrificing performance, the 16-amp stator offers a middle ground. Capable of supplying up to 16 amps of current, this system is well-suited for recreational performance builds and hybrid boats that need to power basic electronics and maintain a healthy charge during longer runs.

The 16-amp stator is commonly found on modified versions of 2.4L and 2.5L engines, especially when the 40-amp system has been deleted to reduce weight.

It works with both aluminum and steel flywheels, as long as those flywheels are designed for low-output (non-40-amp) stators. The 16-amp system strikes a solid balance: strong enough for basic electrical needs, yet light enough to keep throttle response sharp.

This configuration is ideal for bass boats, lake cruisers, river racers, fishing rigs that use electric fuel pumps, stereos, livewell pumps, navigation units, or fish finders. It provides improved idle quality over the 9-amp setup and allows for more reliable operation during extended runs or stop-and-go use.

The 40-Amp System

Beginning in 1989, Mercury introduced the 40-amp charging system on its 2.4L V6 outboards, and by 1991, it became standard on nearly all stock 2.5L engines. The Mercury XR6, 200 EFI, and other consumer models used this robust system to support increasingly complex electronics, gauges, and battery demands.

The 40-amp stator is larger, heavier, and requires a much heavier steel flywheel with more magnets and mass. While excellent for charging power, this system is not designed for racing or high-RPM performance. The increased rotating weight reduces throttle response, and the system is incompatible with 9-amp or 16-amp flywheels and ignition modules.

If you're converting from a 40-amp to a lightweight ignition system, you'll need to replace the flywheel, stator, and voltage regulators.

Flywheel Compatibility

Both 9-amp and 16-amp stators can use either aluminum or steel flywheels—what matters most is that the flywheel is designed for low-output stator systems. Many racers prefer aluminum for reduced mass, while others use lightened steel for added strength and inertia.

The critical distinction is between flywheels for low-output (9- or 16-amp) systems and those for high-output 40-amp systems. The 40-amp flywheel is much heavier and uses a completely different magnetic layout. It cannot be used with 9- or 16-amp stators, and vice versa.

Mixing incompatible flywheels and stators can lead to ignition failure, overheating, or total electrical system damage.

Choosing the Right Stator for Your Application

When deciding between stator systems, it’s essential to match your choice to the intended use of your outboard. If you're building a full-race engine with minimal electrical demands, the 9-amp stator and lightweight flywheel combination provides excellent performance at the cost of charging capability.

For recreational performance, the 16-amp system offers a balanced solution with good ignition quality and enough charging for moderate accessory use.

If your boat came with a stock 40-amp charging system and you don’t need extreme weight savings or racing performance, it may be best to keep the original setup for simplicity and reliability.

But for those seeking maximum performance from their 2.5L or modified 2.4L Mercury outboard, moving to a low-output stator setup is often a worthwhile upgrade—as long as the supporting components are properly matched.