358 Small Block Cylinder Head & Rocker Arm Upgrade - A Different World

Here's something to remember when setting up these heads-the guideplates can be installed either side up. Depending on which cylinder you're on, one side or the other will provide proper pushrod alignment.

We keep mentioning that the World Sportsman II heads this Chevelle was wearing were ported-side by side, you can see why we needed to step up to 235cc heads to get more air in and out of this 358ci.

The 235cc heads require use of an offset rocker arm on the intake side. We contacted Scorpion for a set of its Race Series rockers and upped the ratio to 1.6:1 while we were at it. You get eight regular rollers and eight offset pieces in the set.

On the motor, the need for the offset rocker arms was made readily apparent. The extra 0.150 inch provides the clearance for the big intake ports and the longer valves these heads are fitted with to accommodate them.

Lash on the solid flat-tappet Ultradyne cam was set at 0.16-inch intake and 0.19-inch exhaust. With the 1.6:1 rockers in place, cam specs came in at 0.627/0.622-inch lift intake/exhaust, with 276 degrees of duration on both sides. Lobe separation angle is 106 degrees.

All buttoned up and ready for its retest, our big-headed small-block put on 16 more horsepower at peak-which happened 500 rpm later-while still averaging 4 hp more throughout the powerband. It paid off at the track, where Daeseleer piloted his enhanced Chevelle to a quarter run of 12.35 at 111 mph, three-tenths faster than before. You gotta like that!