The Project 15A motor is a 1993 "L" block B230FT; which has been rebuilt with B230ET pistons.

This gallery will get into what the L block is, and why we chose it for the foundation.

And of course, it is now a tight squish motor.

The decision was made to go with an L block because of the piston cooling via oil squirters. Piston cooling is the way to go to protect the pistons from high heat. And high heat is pretty much a given in a boost motor.

Two things occur as aluminum gets hot:

...its tensile strength diminishes;

...it expands...ie increases in size. AKA thermal expansion.

Aluminum loses strength as the metal temperature goes up; it is less than half as strong at 400F as it is at room temperature. At 600F, aluminum is less than one third as strong as at room temperature. Peak piston temps under boost can approach 600F. Such high crown and ringland temps really weakens the piston...during conditions when you need it to be at its strongest. Add in the size growth while hot, and the piston can get pretty tight in the bore.

Using oil squirters mounted in the block to squirt and spray the underside of the piston crown with engine oil can keep the piston crown peak temps in the 300F range. The piston runs cooler, and thus retains more strength when under the heavy load conditions of boost. By cooling the pistons from below, the piston stays stronger than it would without the oil cooling.

Another way to look at it is this:

...by using a piston cooling system, lighter weight pistons, or cast pistons, can be used in applications that would have required the use of heavier pistons, or the use of forged pistons, in order to have the residual strength at the high operating temps the pistons would reach in a non piston cooled engine.

The cooler running pistons do not expand as much. So the running wall clearances remain more stable and uniform throughout the operating temperature ranges from cold start to fully warmed up heavy load.

Piston cooling is a very good thing.