Boost Or Bust - Honda S2000 Turbo Build

Raceline recommends following the manufacturer recommendations on how much piston ring gap per bore, but depending on the type of applications, Lo says you might have to alter the specs. A prime example would be if the engine is built as a street motor running on Arias Pistons. Lo says, "Go by Arias' specs on piston-to-wall clearance, which they usually recommend three to four thousandths of an inch depending on piston size. Ask your manufacturer if the piston is 2618 forged aluminum, which has no silicone content within the piston, or a 4032 forged aluminum unit, which is a silicone content piston." Both pistons have different expansion rates where the high-silicone content piston will tend to expand more. The 4032 aluminum expands approximately 15 percent more than 2618 aluminum. The 4032 pistons have greater wear characteristics because of the silicone particulate hardening the alloy and reducing the thermal coefficient of expansion. However, a silicone aluminum alloy piston can turn brittle and become prone to fracturing when subjected to extreme stress. This is the main reason why we choose not to use a 4032 aluminum piston in our forced induced S2K, because it will be seeing a lot of cylinder pressure from the large amounts of boost we plan to run through the engine on pump gas.