Counterweights may be designed in different ways to achieve the same balance. State-of-the-art designs have the tip radius (distance from crank axis to "tip" of the crank's throw) for a given balance mass. This may require extensive use of "heavy metal" which is extremely expensive. If an engine is raced on short-tracks requiring rapid rates of acceleration, a low MOI crank may provide a bit less power but should help the car accelerate. Short-tracks, such as Martinsville, will have 10 times the maximum acceleration rate required than (for example) at the Brickyard. If an engine is raced on fast tracks where the maximum rate of acceleration is low, due to high aerodynamic loads (again, as an example), a stiff crank will provide more power but not accelerate the engine/car as well.

What you can apply from this information: All crankshafts are not created equal. Pick the type of crank that best suits your form of racing. Low MOI cranks are more important when required rates of engine/car acceleration are high. If the engine speed does not change significantly and you are on the throttle most of the time, a "stiff" crank may be the best. Do not confuse low MOI with low mass. Mass and moment of inertia are not the same (see Cranks & Rotational Moments of Inertia, page 26). Ask your crank supplier to what tolerances the cranks are supplied. Thoroughly inspect cranks for journal size (and concentricity) and stroke accuracy. Make sure the crank you receive matches the manufacturer's specifications. When building your engine, set clearances accordingly.

Pistons and rings Full-round pistons have not been used in Cup for many years. The current style is the "box-in-box" design (see photo on page 38) with the skirts only on the major and minor thrust sides. The box-in-box design is generally a more mass-efficient design (strength vs. weight). Cup pistons have a minimum mass of 400 grams. Reducing reciprocating mass actually reduces bearing and crankshaft loads. A lower mass piston with an efficient structure may be more durable than comparably heavier components.

Most Cup pistons use a top ring coating to prevent ring welding, and hard anodizing is the most popular coating. Top rings are 0.8mm or smaller and should have a barrel face. Three rings are currently used on most Cup pistons. Remember that the higher the top ring, the hotter it runs and the greater the end-gap required. Also, the hotter the ring, the more it grows in length. Therefore, end-gaps must be adjusted to prevent gap "butting." Always start with more ring-gap than you think you will need, and inspect the ring ends carefully after running the engine to see if any signs of contact exist. Only close the gap when you are sure that the rings will never butt.

The top ring is typically moved up as high as possible. Open engines will have the top ring placed anywhere from 2.3mm to 3.8mm down from the crown. Second rings are usually 0.8 to 1mm and can be barrel or Napier style.

Oil rings are generally 3-piece and range from 1.5mm to 3mm. Oil ring tension relates directly to friction. Cup engines use rings of very low ring tension that are raced only one time. These rings are rated using a tangential gauge and open-class rings rate anywhere from four to eight pounds of tension.

Honing The final finish of cylinder bores is a key element in achieving optimum cylinder pressure sealing and highest power. Piston ring manufacturers are typically able to provide surface finish specifications for the best performance of a given ring package. If they cannot, perhaps you should investigate another supplier. In the same fashion, your machine shop should have a gauge to measure the bore surface finish they're providing. This gauge is important to ensure that each bore is honed correctly as specified.