Anti Detonation Grooves (Contact Reduction Grooves) Plug Reliefs and Fire Slots
Additional cuts that are on the edge of the piston (generally near the valve reliefs) and used to deburr or un-shroud the valves while still on the CNC machine. Various machined slots and reliefs that are used to promote clearance for the spark plug. The plug relief is generally a plunged ball end mill, where the fire slot is a trough in the piston that helps move the spark to- wards the exhaust side of the chamber.
Also know as contact reduction grooves, which limit the piston/cylinder contact during high temperature and high RPM. These grooves also protect the top ring by disrupting detonation waves.
V-shaped groove machined in the 2nd ring land that adds to the volume between the top and second ring. This groove ac- cumulates residual gasses from combus- tion which alleviates top ring flutter and premature second ring wear, improving ring seal.
Cuts that are used to create the deck sur- face on a piston. These are generally used on 4 valve pistons and the compression height is generated from this cut.
CP Groove stands for Constant Pressure Groove. This groove is as a channel on the lower part of the top land and equal- izes pressure to the top ring groove. When used in combination with lateral gas ports, the CP groove helps keep gas ports clear of carbon build up. In addi- tion, the CP groove prevents the top land from smearing into the top ring if the land rubs the cylinder bore
Cuts that are used over the valve reliefs in order to un-shroud the area around the valve.
Double Pin Oilers
Double Pin Oilers (opposed to single pin oil- ers), in conjunction with our annular reser- voir, can add twice the amount of oil from the cylinder wall to the wristpin bore. This is a standard option on any piston that receives forced pin oiling. Broaches are horizontal slots in the pin- bore designed to allow oil to enter between the wristpin and pinbore. Broaches are also used to accommodate the wristpin shape under compression, as it can be- come somewhat oval and needs room in order to alleviate galling. A term used to describe a feature on the piston crown between the intake and ex- haust. Ignited air/fuel mixture on flat top and dish pistons typically have better flame travel than a dome piston. Flame travel on dome pistons can be improved with “fire slots” and/or a combustion trough.
Valve reliefs that are machined in a plunged or circular fashion, designed to leave a boundary around the perimeter to achieve higher compression.
Valve reliefs that have a protrusion in the center of the valve pocket to match the un- derhead shape of the valves. This helps when max compression is the goal.
Radius Valve Reliefs
A Radius valve relief is created by using a form tool (or done in a 3D fashion) to roll the edge of the valve relief. Often times we generate radii from valve relief to valve re- lief (see VR Sweep) as well and this is used to improve flame travel and cross flow in the combustion chamber during the over- lap stroke.
The pin bore is precision honed to attain an exact pin clearance. Depending on the application clearances typi- cally range from .0003 to as much as .003 between the wristpin and bore.