These are the factory Mercury V6 Torque Specs for rebuilding a 1991-2005 2-stroke outboard. Block stamps could include AA, BB, CC, EE, F, FF, NN.

Welcome to our free online Power-to-Weight Ratio Calculator! This tool helps you quickly calculate the power-to-weight ratio of your outboard drag boat and engine combination, which is a key factor in determining overall performance. The power-to-weight ratio is important for assessing the potential acceleration of your boat. How to Use the Calculator: Enter Engine Horsepower (HP) : Input the horsepower of your outboard engine. For example, if your engine is rated at 260 HP, enter "260." Enter Boat & Engine Weight (lbs) : Input the combined weight of your boat, engine, and any other relevant equipment. For instance, if your total weight is 1500 lbs, enter "1500." Calculate : Once you've entered the horsepower and weight, click the "Calculate Power-to-Weight Ratio" button. Result : The calculator will display the power-to-weight ratio, expressed as HP per pound (HP/lb). The higher the ratio, the more powerful your engine is compared to the weight of your boat. This easy-to-use tool will help you understand how well your boat will perform based on its power-to-weight ratio, giving you insights into its improving ET times.

It’s Important to Get the 2-Stroke Fuel-Oil Mix Correct in your Outboard. Engine Longevity: A correct oil mix ensures that your engine is properly lubricated. Too little oil can lead to increased friction, causing severe engine damage or even seizure. Too much oil can lead to excessive smoke, carbon buildup, and poor engine performance. Performance: Using the right fuel-to-oil ratio ensures optimal performance. Incorrect ratios can cause your engine to run poorly, leading to reduced power, inconsistent operation, and hard starting. By maintaining the correct mix, you avoid expensive repairs due to engine damage and help keep your 2-stroke engine running smoothly for longer. Free online Outboard Fuel Oil Premix Calculator Instructions for the 2-Stroke Outboard Oil Ratio Mix Calculator Enter Fuel Amount: In the first box, type in the amount of fuel you plan to use in US gallons. For example, if you’re filling your tank with 2 gallons of fuel, type "2." Enter Fuel-to-Oil Ratio: In the second box, type the fuel-to-oil ratio recommended by your engine manufacturer (commonly 50:1, 40:1, 32:1, 24:1, 20:1, 16:1 etc.). For example, if your manual suggests a 50:1 mix, type "50." Calculate: Click the Calculate button. The result will show how many ounces of oil you need to mix with the entered amount of fuel. Result: After clicking calculate, the required amount of oil (in ounces) will be displayed. For example, if you entered "2" gallons and "50" as the ratio, the result might show "5.12 ounces of oil."

The lower unit gear ratio of an outboard engine is a reduction gear that controls how power is applied to the water. The gear ratio is calculated by dividing the output speed by the input speed. For example, a gear ratio of 1.50:1 means that the engine must turn 1.5 times to turn the propeller once. The gear ratio of outboard and sterndrive motors typically ranges between 1.47 and 1.92. For example, a Mercury Bravo One SM drive has gear ratios of 1.35:1 and 1.50:1. The Mercury 50HP has a gear ratio of 2.31:1. The Seven Marine 627 outboards have a range of gear ratios from 2.33:1 to 1.47:1. Race outboard motors typically have a 1:1 gear ratio and use lower-pitch props. When changing propeller pitch and/or lower units with different gear ratios, it's important to make sure your combination is going to work together. This chart helps to illustrate the impact of changes; for instance, going from 1.60 to 1.75 gearbox might require a propeller 2-3 pitch sizes bigger (maybe 30 to 32 or 33) to run similar RPMs. Conversely, going from a 1.75 to 1.60 might require a propeller 2-3 pitch sizes smaller (maybe 30 to 27 or 28) to run similar RPMs.

Upgrading to lightweight slip-fit wrist pins in your next Mercury 2-stroke V6 outboard (2.0, 2.4, 2.5 Liter) powerhead rebuild will enhance engine performance for outboard drag, tunnel boat, endurance, closed course (circle) and river racers. Here’s how: Reduced Reciprocating Mass: The lighter weight of these wrist pins reduces the reciprocating mass within the engine’s rotating assembly. This decrease allows the engine to operate more efficiently, leading to improved engine responsiveness and higher RPM capability. Enhanced Acceleration: With a lower rotational mass, your outboard’s engine can achieve faster acceleration and better throttle response. This upgrade is crucial for those seeking quicker hole shots and high-performance boating. Decreased Component Stress: Lightweight wrist pins reduce the stress on internal engine components like the connecting rods and crankshaft. This reduction in stress can increase the durability and longevity of your engine, especially under high RPM conditions or heavy load. Potential for Higher RPMs: By lowering the inertia of the engine’s reciprocating parts, lightweight wrist pins can allow for safer operation at higher RPMs, resulting in greater top speed and overall engine power output. This is particularly beneficial for racing or high-performance marine applications. Incorporating lightweight slip-fit wrist pins is a strategic upgrade for any Mercury 2-stroke V6 (150 Black Max, 175 HP, 200 HP, XR2, XR4, XR6, XRI, 225 Pro Max, SST-120, S3000, F1, 260 EFI, 280 ROS, 300 Drag) outboard engine build, offering benefits such as improved engine efficiency, power, and reliability—key factors for achieving peak performance on the water.

Gordon Jennings' Two-Stroke Tuners Handbook  holds particular significance for outboard engine builders due to its detailed exploration of two-stroke engine tuning principles, many of which are directly applicable to optimizing outboard motors. Here’s why it’s important: Optimization of Performance : Outboard engines, especially those used in racing or high-performance applications, benefit greatly from the tuning techniques outlined in Jennings' handbook. Builders can apply his methods to improve power output, efficiency, and overall performance of two-stroke outboards. Porting and Cylinder Design : Jennings delves into the intricacies of port timing and cylinder head modifications, both of which are critical in maximizing the performance of two-stroke outboard engines. Builders can use this knowledge to fine-tune the engine's powerband, making it more suitable for specific marine applications. Exhaust System Tuning : The book provides a thorough analysis of expansion chambers and exhaust tuning, which are crucial for outboard engines that rely heavily on proper exhaust flow for performance. Jennings' insights help builders design or modify exhaust systems to achieve the desired power characteristics. Fuel and Carburetion Tuning : Outboard engines often operate in varying conditions, from idle to full throttle. Jennings’ guidance on carburetion and fuel tuning helps builders ensure that the engine runs optimally across all these conditions, enhancing reliability and performance on the water. Ignition Timing and Engine Reliability : Proper ignition timing is vital for the longevity and efficiency of outboard engines. Jennings’ handbook offers a detailed understanding of ignition dynamics, which builders can use to set up the engine for maximum performance without compromising reliability. Adaptability to Marine Environments : Although the book primarily focuses on land-based engines like motorcycles, the principles are adaptable to marine engines. Builders can translate the tuning techniques to address the specific challenges of operating in a marine environment, such as cooling and corrosion. Legacy and Knowledge Base : For many outboard engine builders, Jennings' book is a cornerstone of their technical library. It has inspired a deeper understanding of two-stroke engine dynamics, leading to innovations and improvements in outboard engine design and tuning over the years. Overall, Gordon Jennings' Two-Stroke Tuners Handbook  serves as a crucial resource for outboard engine builders seeking to enhance the performance, reliability, and efficiency of two-stroke outboard motors. Download the PDF of the original 1973 Two-Stroke Tuners Handbook by Gordon Jennings, Online for Free.

When using a digital inclinometer to measure the pitch of a boat propeller, the "Blade Angle × Constant" method is a straightforward approach used by the Buckshot Racing #77 Formula 1 Tunnel Boat Racing Team. The constant is typically related to the propeller's diameter and the point at which the measurement is taken, which in this case is at 75% of the radius. We've included a proprietary Buckshot Racing #77 Calculator Sheet to make these instructions below much simpler, but included the detail for those who want to take a deeper dive into the math. Tools You'll Need: Digital inclinometer Ruler or tape measure Calculator (Print the Buckshot Racing #77 Calculator Sheet) Steps to Calculate Pitch Using Blade Angle × Constant: Position the Propeller: Place the propeller on a flat, stable surface. Set the Measurement Point: Identify the point that is 75% of the way from the hub to the tip of the blade. This is done by measuring the propeller's radius (half of the diameter). For example, if the propeller diameter is 14 inches, the radius is 7 inches. 75% of this radius is 0.75 × 7 = 5.25 inches. Mark this point on the blade. Measure the Blade Angle: Place the digital inclinometer flat against the blade at the 75% radius mark. Read and record the blade angle shown on the digital inclinometer. Determine the Constant: The constant is derived from the diameter and the position at which the angle is measured. For simplicity, the constant can be approximated as: Constant=Propeller Diameter×π360∘\text{Constant} = \frac{\text{Propeller Diameter} \times \pi}{360^\circ} Constant=360∘Propeller Diameter×π​ This accounts for the propeller’s diameter and translates the angle into a linear distance. Calculate the Pitch: Use the formula: Pitch=Blade Angle×Constant\text{Pitch} = \text{Blade Angle} \times \text{Constant}Pitch=Blade Angle×Constant Substitute the angle and constant into the formula to calculate the pitch. Example Calculation: Propeller Diameter:  14 inches 75% of Radius:  5.25 inches Measured Blade Angle:  20 degrees Calculate the Constant: Constant=14×3.1416360=0.1223 inches per degree\text{Constant} = \frac{14 \times 3.1416}{360} = 0.1223 \text{ inches per degree}Constant=36014×3.1416​=0.1223 inches per degree Calculate the Pitch: Pitch=20∘×0.1223=2.446 inches\text{Pitch} = 20^\circ \times 0.1223 = 2.446 \text{ inches}Pitch=20∘×0.1223=2.446 inches The pitch of the propeller, based on these calculations, would be approximately 2.446 inches per revolution. Notes: Calibration:  Ensure that the inclinometer is properly zeroed before measuring. Average of Multiple Blades:  For accuracy, measure the blade angle at the same point on each blade and take the average. Blade Variations:  Account for any variations in the blade angles by averaging them if necessary. This method provides a simplified yet effective way to calculate the propeller pitch using a digital inclinometer. Download our Free how-to-measure-prop-pitch-calculator-sheet, kindly reference Buckshot Racing #77 when sharing.

While electronic fuel injection (EFI) systems often provide better performance, there are still several advantages to run WH, WMH, WMV carburetors on a Mercury 2.0, 2.4, or 2.5 Liter 2-stroke outboard: 1. Simplicity: Carburetors are mechanically simpler than EFI systems, making them easier to understand, maintain, and repair. This simplicity can be advantageous for users who prefer straightforward mechanical systems. 2. Cost: Carburetors are less expensive than Mercury and aftermarket EFI systems, both in terms of initial purchase and potential repair costs. This makes them a more budget-friendly option. 3. Ease of Repair: Carburetors can often be repaired with basic tools and mechanical knowledge, whereas EFI systems may require specialized diagnostic equipment and expertise. 4. Fewer Electronics: Carburetors do not rely on electronic components, which can be a benefit in harsh marine environments where electronics might be prone to corrosion or failure. 5. Tuning Flexibility: For enthusiasts and boat racers, carburetors offer more hands-on tuning options. Adjustments to the air-fuel mixture and other parameters can be made manually, allowing for customized performance settings. 6. Compatibility: Carburetors can be more compatible with older or simpler outboard engine setups that may not support the electronic control systems required for EFI. While EFI systems generally provide better performance and efficiency, carburetors still offer a range of practical advantages that can make them a preferred choice in certain situations.

In Gordon Jennings' 1978 article in Cycle Magazine on two-stroke oil premix, he observed that using a higher ratio of two-stroke oil in the fuel mixture (meaning more oil relative to fuel) did indeed result in increased horsepower. This finding was somewhat counterintuitive because conventional wisdom suggested that more oil could potentially dilute the fuel mixture and reduce power output. Jennings' conclusion was based on the understanding that the additional oil provided better sealing of the piston rings and improved lubrication, reducing friction and enhancing the combustion process. This improved sealing led to better compression and more efficient combustion, ultimately increasing the engine's power output. The article delves into the following key aspects: Lubrication Needs: Jennings explains that two-stroke engines rely on the premixed oil to lubricate their internal components, as these engines lack a separate lubrication system. Importance of Oil-to-Fuel Ratios: The correct oil-to-fuel ratio is crucial for engine performance and longevity. Jennings discusses how different engines and conditions require different ratios, commonly ranging from 15:1 to 50:1. Oil Types: The article examines various oil types, such as mineral-based and synthetic oils, and stresses the importance of choosing the appropriate oil based on the engine's requirements and operating conditions. Fuel Quality: Jennings emphasizes the significance of using high-quality fuel to avoid engine issues like poor performance and increased wear. Mixing Techniques: Proper mixing techniques are highlighted to ensure an even distribution of oil in the fuel. Jennings advises thoroughly shaking the fuel container and mixing smaller quantities if the engine isn't used frequently. Common Issues and Solutions: The article addresses problems like oil separation, excessive smoke, and carbon buildup. Jennings suggests adjusting the oil ratio and using high-quality oils to mitigate these issues. However, it's important to note that while higher oil ratios can increase horsepower, they also result in more smoke and potential carbon buildup, so the optimal ratio needs to balance power output with engine longevity and cleanliness. You can download the full copy of Gordon Jennings' 1978 article on two-stroke oil premix here:

Outboard engine manufacturers often use roller bearings instead of friction bearings (such as plain bearings or bushings) in 2-stroke engines for several reasons: Load Handling Capability: Roller bearings, particularly needle roller bearings, can handle higher radial and axial loads compared to friction bearings. This is important in outboard engines where the crankshaft experiences varying and sometimes significant loads due to the nature of marine propulsion. Durability and Reliability: Roller bearings are generally more durable and have a longer service life than friction bearings. They are designed to withstand higher stresses and provide consistent performance over extended periods, which is crucial for the reliability of outboard engines operating in harsh marine environments. Reduced Friction and Heat Generation: Roller bearings typically exhibit lower friction compared to friction bearings, which reduces energy loss and heat generation. In a 2-stroke outboard engine, minimizing friction helps optimize fuel efficiency and overall performance. Compact Design: Roller bearings can often be designed to have a more compact profile compared to friction bearings of similar load capacity. This compactness is beneficial for packaging within the constrained spaces of outboard engines. Maintenance Considerations: Roller bearings generally require less maintenance compared to friction bearings. They are less susceptible to wear and typically do not require lubrication or replacement as frequently, reducing downtime and maintenance costs for outboard engine operators. Industry Standard: Roller bearings have become a standard choice in modern outboard engine designs due to their proven performance and reliability. They are well-suited to handle the operational demands and stresses encountered in marine applications. Overall, the use of roller bearings in 2-stroke outboard engines is driven by their superior load handling capabilities, durability, reduced friction, and suitability for marine environments. These factors collectively contribute to improved performance, efficiency, and reliability of outboard engines. *Picture here is the original patent for the Upper Main Bearing found in the Mercury 2.4 Liter 2-Stroke V6 Outboards with 1 3/8" top journal on the crank. AKA the OEM part number 93496, 31-93496T or RBC TJ-75117-11 filed under Patent 3382016 "Arrangement of tandem rollers in a roller bearing and method of assembling same". This bearing was designed to handle 8,500 RPMs and was selected for the motor based on: Load Distribution: Tandem roller bearings are designed to handle heavy radial and axial loads simultaneously. They distribute the load across a larger surface area compared to single-row bearings, which can improve bearing life and performance. High Load Capacity: They are capable of supporting higher radial and axial loads, making them suitable for applications where significant forces are acting in multiple directions. Reliability: These bearings have been used for many years in various industrial applications, indicating their reliability and established performance in demanding conditions.

Here are the standard Factory Carb Jet Sizes for Mercury Racing 2.4 Liter Bridgeport, 2.4 Liter MOD VP, and 2.0 Liter XR2. This Jetting Chart includes the Mains and Idles that were found in the WH46 and WH48 Carburetors.

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.