HOT ROD SED SHOP offers an oem Ski-doo cylinder head machined for optimum performance for your sled. This increases the compression slightly, and offers better combustion burn. Gains of 4hp are common. We have no detonation or driveability issues with these heads. Customers must provide the squish of their stock head measured "old skoo" with solder. We have these on the shelf -ready to go for most stock motors with stock base gaskets in them. We can offer special specs. for altering your base gaskets/prt timing which will affect your squish.