High Performance Liquid Cooled 2-Stroke Cylinder Head Design

High performance 2-stroke engines, specifically those found in motocross bikes, have declined over the years due to stricter emissions regulations and the increase in 4-stroke engine technology and performance. This decline means that there is not much information or research being performed to optimize the engines and how to design for certain performance characteristics. The goal of this project is to change and improve the performance of a 250cc liquid cooled 2-stroke engine for different dirt bike riding situations.

One of the best ways to do this was through designing a custom cylinder head. The cylinder head was designed to be a two piece assembly so that multiple combustion chambers could be manufactured and interchanged to research different combustion chamber parameter effects on performance, and in the end use them for different riding situations and power delivery preference. This research and design will establish the relationship between a few combustion chamber parameters and real world engine performance and power characteristics. The parameters changed over the OEM head are the squish band angle and area, piston to head clearance, compression ratio, combustion chamber shape, and coolant volume in the cylinder head. The combustion chambers were designed using the Bimotion Cylinder Head program, and then used in whole assembly that was designed in PTC CREO.

This project is still a work in progress, but the research and design is complete. The next steps are manufacturing the cylinder head parts and testing the performance change on the engine. The performance will be tested on a dynamometer and in real world riding conditions, such as low speed technical trail riding, high speed motocross racing, and leisurely trail riding. This will be done to see which combustion chamber performs the best for each situation, if there is any considerable difference, and if there are any reliability issues with the design such as engine overheating, cylinder head cracking, or mechanical failure. This research will validate theoretical engine design and give more insight on how to apply head design parameters in the future.