The logic to achieve the airflow goals went something like this: To get good low- and midrange flow, start with a bigger valve. The usual deal here is a 2.02-inch intake, although some of the current big-port street heads do sport intakes of 2.08 inches. Here Kaase elected to go to a 2.10-inch intake as a starter.
Now as good a move as a bigger-than-normal intake sounds, it could run foul of the negative effects of valve shrouding. The stumbling block here is that the bigger the valve used, the more potential there is for valve shrouding to cut into the bigger valves' potential gains. So is all lost? Not really, because shrouding of the exhaust valve by the cylinder bore is of far less consequence than it is for the intake. Because the valve is smaller, the close proximity of the bore produces a much lower percentage loss of flow. But there's more. At a lift value of about one-quarter of the valve's diameter, the flow pattern changes because the valve has moved sufficiently far from the seat to be close to leaving the field of influence of the valve head to the valve seat. Since the valve is only 1.6 inches diameter, it reaches this critical lift point at 0.400 inch instead of about 0.525 for the intake. Because this critical point takes place at a lower lift, a normal exhaust valve would spend more time in the near non-shrouded, higher-lift range. OK, so the exhaust situation is looking good, but it does not, as we shall see, end there.
Most of the engines on which we are likely to install a set of heads such as these will almost inevitably be relatively high compression. The higher an engine's compression ratio, the more exhaust flow can be traded for additional opening duration to compensate. In short, the higher the compression ratio, the more you can trade exhaust valve size and flow for intake size and flow. With the forgoing about exhaust shrouding and flow in mind, Kaase made a move that has often been shunned by other head designers. Namely he moved the exhaust valve closer to the cylinder wall so as to give room to move the intake towards the middle of the cylinder. This cut the intake valve shrouding, thus giving the intake valve a much better chance of flowing more air at low lift. As a last move, the intake was inclined at about a 5-degree angle so, as it opened, the periphery of the valve moved further away from the adjacent cylinder wall.
At this point all looks well on the flow side, but this had to be accomplished while retaining good valve-to-rocker geometry. This was achieved to the extent that not only was the need for piston-valve cutouts vastly diminished, but also any 1.6 or 1.7 Ford rocker using a 71/416 stud would work, except maybe those with a wide body.
The Ports - With a combustion chamber configura-tion that held great promise for strong flow figures throughout the lift range, it became obvious the intake port itself had better work well or all the chambers assets will amount to near zero. Kaase opted to make the port enter the head and sweep upward more than usual. This allowed for a deeper bowl and a bigger short-side turn (also called the short-turn radius). Both these moves contribute to improved flow in the mid- and high-lift regimes. It also produces a longer than normal port so the 247 cc this port has is not directly comparable to a more conventional head.
What we have here is a head that has about the same areas as a conventional one of about 220 or so cc's. That's still big, but the cross-sectional area is well utilized. Added to this, the high flow means that a lot of air is going through the port so that port velocity is more akin to a head in the 200-215cc range. Our flow tests showed, at an extremely credible 296 cfm, the highest as-cast figures so far seen. As such, our numbers are somewhat lower than those you will see in Jeg's catalog, but don't let that be a source of disappointment. The bench we use has the calibration checked with a Helgesen plate almost every time a project head is flowed. Flow figures from industry benches almost always run higher than ours.
The exhaust port flowed well...
The exhaust port flowed well in as-cast form to the extent that it was one of the better ones we have tested.
With the valves in place,...
With the valves in place, the close separation of the intake to exhaust can be easily appreciated.
This view down the T&L-ported...
This view down the T&L-ported Jeg's/Kaase head highlights the port shape. The port floor rises more than most, and as it rises into a deeper-than usual pocket, the port spreads in width. This makes for a larger and more effective short side turn.
The T&L port work on the Kaase...
The T&L port work on the Kaase head, even in its simplest form as a clean-up, delivered 236 cfm. Given a little more leeway, T&L quickly got this up to 245 cfm. That is something nearer the true potential of this stock-position exhaust port.