|Originally developed in 1955 at 265 cubic inches, the small block Chevy engine has evolved into the most popular engine in history. With literally millions
of factory production units in circulation, the performance aftermarket has exploded with countless variations of this engine. When choosing a piston, the
choices can be reduced to a few simple steps.
Piston to cylinder head compatibility is determined by two major factors, dome shape/size and valve relief (VR)
placement. VR placement on the piston is influenced by two characteristics of the particular cylinder head being
used; valve angle and valve spacing. The following paragraph discusses the VR placement characteristics of the
most popular small block Chevy cylinder head, the 23º.
Factory GM heads are used to define standard valve spacing and angle (thus 23º) for many small block Chevy’s.
Additionally most 23º aftermarket cylinder heads incorporate what is commonly known as "60/40 Shift" (See
diagram at right) in order to allow for larger valves. All JE flat top and inverted dome shelf piston designs
accommodate "60/40 Shift" and will work with most aftermarket 23º cylinder heads, including those with
oversized valves and angle milled surfaces. TFS "Twisted Wedge", AFR227 and Brodix 10X cylinder heads
will require custom pistons.