Pontiac GTO 400 Engine Block Build Up - Poncho Honcho

You can see the 7/16-inch screw-in rocker arm studs and included pushrod guideplates as the head bolts are torqued in sequence.

Valvesprings and retainers are Comp Cams-issued. PRW full-roller, forged aluminum rocker arms are plainly stamped with the engine size, stud diameter, and rocker arm ratio. Valvetrain geometry must be fully checked on every engine with aftermarket heads, especially aluminum, because spring pads and valve placement can be slightly different compared to stock, so proper roller rocker arm tip-on-valve stem positioning must be verified.

Since Pontiac never used round-port heads in a '61 model, Middleton had custom headers built to run the Edelbrock heads in his Catalina. Mark Delcamp, proprietor of Mad Dog Exhaust Products in Allen, Michigan, makes the company's headers one set at a time. He's been at it since 1989 and before that was a honcho at the legendary JR Headers in Detroit. These early Pontiac headers feature heavy-duty 16-gauge (0.065-inch wall) tubing.

A Pertronix electronic ignition conversion is hiding under the distributor cap. ACCEL wires deliver the spark to NGK FR-5 plugs.

Sherman adds a 1-inch spacer to the Performer RPM intake manifold, which he says is worth an additional 10 hp. As well as providing WOT power, since the 800-cfm AFB carburetor features primary metering rods that work off engine vacuum, they can meter fuel 12 percent leaner or richer, benefiting performance or economy-depending on how the engine is being used. Hood clearance with the RPM intake and spacer might be questionable on some Pontiacs, but not Orwin Middleton's '61 Catalina.

Sherman had the new harmonic balancer "degreed" from 10 degrees after top dead center (TDC) to 50 degrees before. After degreeing-in the camshaft, he had to make a new timing pointer. He also marked in white: TDC, the pointer tip, plus 30 and 40 degrees before TDC. Exact engine timing is a MUST! It should also be noted that the 455 had the benefit of being dyno-tested with no pulleys or drive belts, per se. This can save 6-7 hp.