Chevrolet 406 CI Engine Build - Impersonator II

There are two Edelbrock RPM Air Gap intake manifolds for the small-block Chevy. The PN 7516 (Vortec) piece uses eight attachment bolts, and the PN 7501 (standard) unit uses 12 bolts.

Notice that the rocker on the left is self-guided and features two rails that hold the rocker over the valve stem. The rocker on the right is conventional. It doesn't need guide rails and the pushrods are steadied by guideplates designed to keep the rocker centered over the valve.

The Vortec heads feature a 174cc intake runner, whereas our AFR castings sported 180cc intake runners. Because these were relatively close, the torque numbers remained the same, but at over 4,000 rpm, the AFR head port design shined over the Vortec.

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The carbon buildup around the intake port is due to the intake-runner design inside the Vortec head and doesn't necessarily mean that the combustion chamber is inefficient. Don't worry about porting the spark-plug boss out of the chamber.

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When AFR heads are assembled at the factory, the screw-in rocker studs are not torqued down. Before running the heads, we torqued our studs to 60 lb-ft.

With 527 lb-ft of torque and 490 hp, you can make almost any small-block Chevy into an 87-octane-drinking, 11-second quarter-mile hero.

We swapped off our 1.5:1 aluminum-body Comp Cams roller rockers for Comp Pro Magnum series 1.6:1 rockers. The fact that our engine needed more camshaft resulted in 13 more peak horsepower.