Words by Ray T. Bohacz - Photos by Moore Good Ink

In every class of motor sport, engine power is increasing in impressive leaps.

Even small displacement engines now produce horsepower
that only ten years ago was considered the realm of highly
refined and exotic mills hundreds of cubic inches
larger. And sizeable cubic inch power plants
regularly produce over 1,000 horsepower
in street trim with a cast aluminum intake
manifold and a single carburetor. There
seems to be no end to the power

Cylinder head technology with
increased air flow and combustion
chamber design has led the charge.
Many of these advances have been
accomplished by improving the
performance of the valve train, achieved
largely by state-of-the-art test and
development equipment such as the
Spintron, and also by the latest
machining centers.

The enthusiast community measures engine power in terms of horsepower and torque. But cylinder
pressure read as BMEP and IMEP are
more accurate indicators. These
abbreviations refer to Brake Mean
Effective Pressure and Indicated
Mean Effective Pressure, which are
more precise measurements since
gas pressure in the cylinder varies
from a maximum at the beginning of
the expansion stroke to a minimum
near its end. Also, these classifications
can very accurately compare the power
of engines of different displacements
since it is the pressure per piston area
that is being examined.

Recognizing that cylinder pressure is the true
dynamic that creates horsepower compels one to
consider the piston and the forces applied to it. In high performance and racing applications the piston needs to withstand and then transfer the cylinder pressure to the crankshaft while it also maintains its shape, provides a long service life, partakes in sealing the bore, and compliments and not detracts from the effectiveness of the cylinder head and combustion chamber. That’s a long list of tasks!
While it may look like a lot of work to whittle a finished piston from a bar of aluminum, with the advent of today’s CNC machining centers it takes very little effort once the original design is programmed into the machine.
NASCAR teams might have been the first to use billet pistons, but that technology has spilled over into Pro Stock drag racing as well as other classes. Along with a measure of exclusivity, it’s given teams the ability to experiment with piston designs hitherto not available with a forging.