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Will a Big Bore Mercury Piston make more HP?

A big bore kit, also known as a top-end kit, is an upgrade for a 2-stroke outboard high-performance engine that increases the engine's displacement by enlarging the cylinder bore size and replacing the pistons and rings.

This rebuild modification allows for increased air/fuel mixture into the engine's combustion chamber and high compression with the same size combustion chambers, resulting in increased power output and torque.

By increasing the engine's displacement, a big bore kit can enhance the overall performance of the engine, providing more horsepower and better acceleration for applications such as racing or high-speed boating.

To calculate the HP increase in a Mercury 2.5 Liter racing outboard when the engine displacement is increased to 2.6L, we need to know the exact HP rating and/ or configuration of the original engine.

However, we can make an educated estimate based on typical HP ratings for engines of this size. We know the Mercury V6 2.5L 2-stroke outboard engine was produced to make anywhere from 150 to 300 HP, depending on the specific model and design.

Assuming a baseline HP rating of 200 for the Mercury 2.5L outboard, an increase in displacement to 2.6L might result in a 2-5% increase in HP. This is based on the assumption that other factors such as engine design, compression ratio, and fuel quality remain constant. So, the HP increase might range from 4 to 10 HP, resulting in a new HP rating of 204 to 210 HP.

It is essential to ensure that the engine is properly tuned and maintained after installing a big bore kit to optimize performance and prevent any potential damage.

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