We raised the roof considerably with a tapered cut limited by the port window and the thin
In an effort to gain more port area in the runner, we considered the available space. The runner has four sides-the roof, the floor, and the port walls. Generally, dropping the floor to gain area hurts flow, so we were left with the walls and roof. The straight side of the wall is constrained by the oil-feed passage and the head-bolt bulge, while the dogleg wall is limited by the casting thickness. We widened the full length of the runner by working both walls, taking care not to cut excessive material in the aforementioned danger areas of the straight sidewall. The port responded favorably to the increased area, breaking the 300-cfm barrier and improving incrementally through most of the lift range.
At this point, finding more area became increasingly difficult. We wanted to avoid cutting the floor, and with the walls widened as far as was practical, the only direction left to go was up. We also wanted to retain the factory port window at the manifold opening, which represents the constraint at the opening of the port. At the far end of the port, deep in the runner, the height was limited by the thickness of the material under the spring-seat machining. Between these two points, the only limit was the casting thickness, which allowed for significant metal removal.
We carefully measured the thickness of the roof at the spring-seat machining and marked the location in the port to avoid cutting too deep in this critical area. The roof between the opening and the marked thin spot under the spring seat was given a deep cut. The depth of metal removal tapered from the port opening (where nothing was removed) to about .150 inch by mid-port, where it tapered again, leaving .080 inch at the near side of the spring-seat machining. It was an involved reworking, giving the roof a concave shape rather than its original flat form. Port flow in the high-lift range improved handily but was out of the range of street/strip valve lifts.
The dogleg wall and floor are shown here after cutting. Note the smooth radius away from t
At this point, the runner size was maxed out, so our attention returned to the bowl area, which, as noted before, was already nicely formed and sufficiently large. In our judgment, the throat area was already near optimal size, and further enlargement of the area immediately under the seat would be a detriment to flow. We lightly blended the bowl as well as the short turn. As we suspected, the bowl area was already well executed in the as-delivered heads, and we saw little benefit in the street lift ranges, though the very top of the curve showed an appreciable improvement.
Our final modifications to the intake port was to break out the cartridge rolls and flap wheels, and polish the port. Polishing removes minor irregularities and further enlarges the port. Again, we saw gains only at very high lifts, most likely attributed to the smoother contour in the port-throat transition and short-turn.
As with the intake ports, the out-of-the-box flow of the E-head's exhaust ports were at a level typical of a well executed, fully ported production head (Table 2). We noted some ridges where the machining of the port exit met the as-cast surface and began our modification sequence by blending the port exit into the runner. However, only a modest improvement resulted.
The large, open bowl needed almost no further enlargement, only a little brush-off to blen
Fully ported and polished, our intake delivered 320 cfm, but most of the gains were up-out
On the exhaust side, we began by removing the "eyebrow" where the exit machining meets the
As with the intake side, the exhaust valveguide boss was minimally intrusive, and profilin
Unlike factory iron heads, the exhaust port has a nice short-turn form. We carved it mildl
Raising the roof .100 inch gained flow up top. However, this is the case only if the cut i