Heads and Cam
In contrast to the heavily production-biased bottom end, the top end of the engine takes advantage of aftermarket products and significant modifications. Semchee details the cylinder heads: "I used the Kauffman high-port heads, and I had Darrin Morgan port them. We added the epoxy to get the port velocity up, and above the epoxy the heads were widened and raised. The intakes flowed 400 cfm at .900-inch lift, but of course we are not lifting the valves that much. The flow adds up to horsepower, but you have to consider the velocity too; you have to consider the two together. I wanted to keep the heads as small as possible. Just by comparison, the heads are smaller than the large Pontiac Ram Air IV iron castings, but flow a lot more."
To operate the valves, Semchee relied on the expertise of Bullet Cams: "We kind of had an idea of what we wanted and talked to John Partridge at Bullet and had him finalize the cam specs. We were a little tight on time, so we couldn't experiment much on the cam. The cam measures 240/248 degrees duration, ground on a lobe separation angle of 106 degrees. We use a mixed set of Crower and COMP rockers at 1.7/1.65:1 ratio because we had to slow the exhaust down a little. It was scavenging too much and losing power, so we reduced the ratio. We made the change and picked up around 20 hp."
Semchee continued on the valvetrain: "The lifters are Scorpion limited-travel hydraulic rollers. Whether you need them depends on the profile of the cam. If it is not that radical, you can use the regular lifters, but if you lose stability, it will be very hard on the valvetrain. With the high spring pressure and the radical cam we used a stud girdle to stabilize the valvetrain. We also went with a beltdrive system, which is a real benefit in a higher powered engine. With the beltdrive, it is just a five-minute job to alter the cam timing without having to tear the motor apart. It makes it very easy to tune, and you can pull the cam easily without having to do as much disassembly to the front of the engine."
Semchee disclosed that the fuel delivery system was one area where the engine build plan strayed off course: "We were originally going to run an EFI combo on a single-plane intake manifold, but we ran into problems. With time running out to prepare the engine for competition, we threw the carb on it with a two-plane intake. We probably lost 60-70 hp compared to the big intake on the EFI system, but as it turned out the control box was bad. The Edelbrock Performer RPM manifold was nearly box-stock, other than filling the bottom of the ports to match the heads. We really did not have much time to work on it. We did have a very good Holley carburetor on the engine. The carb was done by the late Keith Dillard, and it was pretty extensively reworked. We had used the carb in the past and found that it worked much better than one out of the box."
A set of custom headers was fabricated with a stepped primary configuration featuring 1¾ - 1⅞-inch primary tubes. The headers were fitted with a pan evacuation system drawing crankcase pressure into the collector. Semchee disclosed: "The crankcase ventilation makes some more power. The shape of that tube in there is very critical, as is the angle it is on, and the length it is in there. Ray Clayton did extensive testing on the flow bench to find the placement, angle, and shape, and it made a difference. Overall, to put a number on it, we found around 5 hp with this system."
To The Dyno
The engine was dressed with a full MSD ignition system including an MSD 7AL-2 Plus control box, which is programmable, but it was set for a straight 36 degrees advance for total timing. Bolted to the DTS Powermark engine dyno at the University of Northwestern Ohio, this hot Pontiac combination had the opportunity to prove its worth. Running on VP unleaded fuel, the Poncho showed a power curve right on target for serious street action. With just 408 ci, the torque curve displayed tire-frying twist, with 436 lb-ft on tap at a lowly 2,500 rpm, and a peak of 535 lb-ft at 4,700-4,900 rpm. That's torque in abundance in an rpm range where you can really use it. Power came in at a healthy 546 hp at a modest 5,800 rpm, again just in the range for usable street output.
As Semchee tells us: "What is great now is all the aftermarket support with the heads and other parts. Years ago we had to run the factory iron heads and you'd pay a lot for a set of iron Ram Air IV heads. For a street/strip car, you might not even want to run the high-port head, but for an application like this the high-port heads improve the flow and allow more top end horsepower." The combined efforts of a vibrant aftermarket and the unwavering enthusiasm of Pontiac specialists like Semchee assures us that Pontiac's legacy will indeed live on!