Exhaust Port template
Below are downloadable files from Wax Racing, offering traceable templates for 3D-printable exhaust ports. To access a file, simply click on the desired link, and a download window will open.
Make sure to download the file specific to your ski and engine configuration. For example, if you are working on a 760 cylinder (84mm), download the corresponding STL file and print it. Porting based on this template will result in a 195-degree exhaust duration and a 65-70% exhaust port-to-bore ratio. These calculations are based on a 0.7mm deck height, where the piston sits 0.7mm down the bore at top dead center (TDC), which is common in production engines.
If the cylinder is machined to achieve a zero deck height, where the piston is flush with the top of the bore at TDC, the exhaust duration will adjust to 192.5 degrees. Why is achieving zero deck height recommended? It allows you to properly set the squish clearance, an essential aspect of optimizing engine performance. This topic will be covered in greater detail in an upcoming article.
A 70% exhaust port-to-bore ratio is ideal for pure race engines but is not recommended for surf engines where durability and extended ring life are priorities. Additionally, ensure a proper chamfer is applied to the ports to guide the rings smoothly into the piston, reducing wear and prolonging rebuild intervals.
These exhaust port designs are based on configurations we use in our engines, but they are provided for reference only. Use them at your own risk.
Yamaha engines
Kawasaki engines 750-800