Our next modification was to streamline the as-cast guide boss. As we noted, the guide bosses on both the intake and exhaust of the R/T heads are diminutive, particularly as compared to production heads. Paring them down to a race fully-ported shape takes some finesse, and is worth a modest improvement in higher lift flow (tables 1 and 2, column three). Next, we went in for a minor clean up of the short side turns of both the intake and exhaust ports. With the nice, as-delivered, short side shapes, our gains were minimal, though the intake picked up at the top of the curve, now breaking over 260 cfm (tables 1 and 2, column four). Focusing on the intake port, some checking with a velocity probe showed high airspeed over the peak of the pushrod hump. This indicated the port flow could be improved by paring down the pushrod restriction. The pushrod bulge in the port runner is cast to very close tolerance, so unlike many castings there isn't a large amount of excess material here. carefully gauging the metal thickness with a Helgesen E-tool, we were able to trim the material to a consistent .040-inch, enhancing the cross-sectional area available at this constriction. Opening the pushrod pinch in this fashion netted a good incremental gain in intake port flow (table 1, column five).

At this point most of the minor porting tricks had been applied. there was little left to do other than pursue a fully ported form. Both the intake and exhaust runners were gasket-matched, and the runners were cleaned up with a long carbide cutter. We didn't significantly alter the size or shape of the as-cast port, but rather eliminated the rough surface and created a flat, straight approach from the runners into the bowls. On the intake side, the flow was basically unchanged, although the exhaust gained substantially (tables 1 and 2, columns 5 and 6). The intake port shape was definitely better, but since we worked the runner from the manifold side only, the improvement in runner shape was largely negated by a less than ideal transition into the previously worked short turn and bowl. We would remedy this with our next mod. On the exhaust side, working the runner showed an immediate benefit, boosting the flow to over 210 cfm. as with the intake side, the runner was worked entirely from the flange side of the head, owing to the straight access to the entire port. the exhaust runner work made a nice transition into the previously cut areas.

The final mod was to fully polish both the intake and exhaust ports. While the physics of boundary layer airflow would predict little benefit to surface enhancement of the port in terms of flow potential, the reality is the aggressive carbide-cut surface of our porting efforts to this point left a far from ideal form. The subtle transitions from the runner to the bowls, around the short turn (particularly in the corners), in the vicinity of the guides, and from the bowls to the seat bottom-cuts were all simply roughed-out by the carbide cutting. Polishing would allow us to clearly see these flaws in the shape, and derive the maximum benefit from the mods made to this point. Finishing the ports with polishing improved flow significantly on both the intake and exhaust (tables 1 and 2, columns 6 and 7).