[Steve Chryssos]

Trev,
This specification refers to the inclination of the valves relative to the deck. Small block Chevy engines were originally designed with 23 degree valve angles. Shallow valve angles are an evolutionary feature. First it was determined that the original small block Chevy cylinder head could benefit from raised port locations. Raised ports provide a straight shot towards the valves. Then engine builders realized that the raised port designs could be further enhanced by "rolling" the valve angle back towards zero.

So there really isn't any case where 23 degree heads are better except for price. Furthermore the "secret" to LS-x performace potential is exactly the fact that the heads feature extremely shallow valve angles and raised ports. GM simply applied the existing GEN1 shallow angle/raised port technology to their production engines.

To install 18 degree heads on a GEN 1 small block, you must also convert the valvetrain, intake manifold and headers as well. In some cases you may need different pistons (i.e. a BUICK symmetrical port conversion). And 18 degree castings are generally sold in semi-finished form. So add the cost of professional porting as well.

In short, an 18 degree (or 14 degree) conversion will cost you as much as a stout LS-x engine. Unless you absolutely, positively must have a shallow angle/raised port GEN1 small block, the cost for conversion is prohibitive.