Piston Terminology

When you’re ready to purchase a set of performance pistons you are bound to come across some unfamiliar terminology. The following should help give you a better understanding. Ultimately, the true expertise will lie with the manufacturer of the pistons that you choose. Being able to communicate your requirement in an intelligent fashion will allow you to get the right set of pistons the first time.

4032

This is the popular low-silicon alloy used by piston manufacturers. This is a great choice for street performance use and it has also seen limited competition usage overseas.

2618

This is the popular zero-silicon alloy used by piston manufacturers. This is a great choice for street performance or competition. This is the most popular alloy for competition use.

VALVE POCKETS

To get the proper clearance for the valve, valve pockets are machined into the crown of the piston. When longer duration and higher lift camshafts are being utilized, valve pockets should be cut for proper piston-to-valve clearance.

PISTON WEIGHT

Whenever the weight of the piston can be reduced, the stress on the connecting rods can also be reduced. Reducing weight also decreases reciprocating mass which allows the engine to rev easier.

PIN MATERIAL, WEIGHT, DESIGN & DIAMETER

The function of the piston pin is to make the connection between the piston and the rod. The pin is a highly stressed component. In some cases, superior materials may be available. These materials provide good insurance at a small cost. Larger diameter pins will support higher power levels given the same wall thickness.

PISTON SKIRT COATINGS

A number of aftermarket companies provide coating services for pistons. Additionally, a few manufacturers offer pistons with coated skirts. The skirt coatings are designed to reduce the friction between the skirt and the cylinder.

OFFSET PINS

On some applications, offset pin locations can be utilized to reduce piston noise.

PISTON CROWN COATINGS

A number of aftermarket companies provide coating services for pistons. Ceramic-metallic coatings on the piston crown can provide an additional thermal barrier.

INTERNAL MILLING

The design of the forging will be the determining factor of the pistons overall weight. However, internal milling can remove unnecessary material from the pistons structure.

GAS PORTING

Vertical and horizontal gas ports are sometimes employed to aid in ring sealing. In general, vertical gas ports are used for competition engines where horizontal gas ports are used in both street and competition applications.

FIRE SLOT

On domed piston applications, some manufacturers will machine a “fire slot” in the center of the piston. The intent of this design is to aid in the combustion across the entire piston.