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Writer's pictureMike Hill

Can two-stroke oil make HP in your outboard?

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:


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