MAC Headers and Cats The next phase involved replacing the stock tubular exhaust headers and catalytic converters with MAC 1 5/8–inch diameter headers (stock headers primaries are 1 ½–inch). They put the car in the 12s for the first time (12.95 at 108.04), and power at the wheels jumped from 306 hp/321 lb–ft to 325 hp/339 lb–ft. The MAC catalytic converter was flow–tested against the stock Camaro SS unit and found to be slightly more restrictive—293–cfm versus the OE’s 304–cfm measurement. The difference is fairly insignificant, so the boys left it alone.

Ported Heads
A sand–casting of 356T6 aluminum, the LS1 cylinder head was designed by a team led by GM Powertrain Cylinder Head Release Engineer and Chevrolet Race Shop alumnus, Ron Sperry. Responsible for such landmark designs as the raised runner NASCAR small–blocked head and the symmetrical–port NHRA Pro Stock head, Sperry focused on maximizing volumetric efficiency at all engine speeds—no mean feat. For a production piece, the stock LS1 head is fantastic. At 28 inches of mercury and at 0.650–inch lift, the intake port flows 238 cfm while the exhaust port flows 179 cfm. S.A.M. students carefully smoothed the LS1’s replicated ports and replaced the stock 2.00(I)/1.55(E) valves with Ferrea stainless, 2.02(I)/1.60(E). This netted an extra 50 cfm on the intake side and 32 cfm on the exhaust (both measured at 0.650 lift). Performance increased to 12.78 at 111.30. Chassis dyno readings revealed 349 hp and 358 lb–ft.

LS1 ports are replicated to ensure equal port flow volume to each cylinder. Using care not to disturb this balance, S.A.M. students found additional flow by removing restrictions and polishing. Only four head bolts encircle each cylinder, making the LS1’s unique "cathedral"–shaped intake ports and D–shaped exhaust ports possible. Each of the extra–long head bolts is anchored by the main bearing web area for maximum clamping capability.