The scavenging effect was so pronounced that the Semchee team felt some intake charge might have been pulled out of the exhaust port. They experimented with a bigger header primary diameter to lessen the draw at lower rpm levels, and actually gained low-rpm power by doing so! It's rare to gain low-rpm power by going to a 2.250-inch primary pipe on a 409ci engine, but this team did it. The beautiful headers were made by Custom Header and Exhaust out of Columbiana, Ohio, and they measure in with 42-inch primaries feeding into 3.5-inch collectors.
With the cylinder head potential understood, the camshaft could be designed to optimize performance in a given rpm range. Mike's partner in this engine, Ray Clayton (of Ray's Dyno and Machine), worked directly with the experts at COMP Cams, and also with Jeff Kauffman to optimize the cam design. The final specs ended up with duration at 254 at .050 on the intake side, 260 at .050 on the exhaust, with lobe lift numbers checking in at .369 inch on the intake, and .372 inch on the exhaust. When multiplied by the rocker ratios (1.75:1 on the intake, and 1.65:1 on the exhaust), the cam's lift numbers become .645 inch at the intake valve and .613 inch at the exhaust valve. The cam's lobe separation angle was a mere 106 degrees, so there was plenty of overlap to pull intake charge in while the exhaust was leaving.
Mike admits he and Ray were rushed to get the engine together and to the Challenge on time, and it cost them. Beyond the compression ratio being lower than they'd hoped, the valve-springs were found to be a bit light. Then, oil pressure started dropping. It didn't look good, but the teardown after the Challenge showed where the problems lied. The light valvesprings allowed the valves to stay open at the higher rpm levels, allowing the pistons to come in contact with them and bending every intake valve. As the Challenge competition continued, the team was losing power with every pull.
Feeding fuel to the engine was a job for a modified Edelbrock Victor intake manifold and a Holley HP 950-cfm carb, with a Holley spacer plate sandwiched between them. The intake's dividers were extended about .750 inch further into the open plenum of the single-plane design to increase runner length, which straightens out the air/fuel charge before it meets the cylinder head intake port. The downside to this is that it takes up valuable plenum volume, but the team was able to make up for it by using the open spacer plate. Naturally, the intake manifold's ports were modified to match up with the modified Kauffman intake ports.