With the advent of Vortec cylinder heads on most crate engines from General Motors, this leaves you with a little problem. Your ’87 is equipped with an EGR valve and requires an exhaust crossover in the cylinder heads to feed the intake manifold. Neither the Vortec nor the L98 aluminum cylinder heads used on the ZZ4 engines have these provisions. We’ve come up with two options using Chevrolet Performance partial engines. This is where GM offers the short-block from its popular crate engines. The ZZ4 partial assembly (PN 12561723) comes with forged crank, powdered metal connecting rods, LT1-style, high-silicon pistons that feature flat-tops and four-valve-relief, four-bolt main block with provisions for a hydraulic roller camshaft and lifters. This is a great foundation for a performance build with a factory warranty.
Next, take a look at the HT383 partial engine assembly (PN 12499106). This fully dressed short-block features the same four-bolt roller cam block as the ZZ4, 4340 forged steel 3.80-inch stroke crankshaft, special powdered metal 5.7-inch connecting rods that feature a stud and nut to retain the rod cap. This gives you the clearance necessary to clear the camshaft in a stroker application. Speaking of camshaft, it comes equipped with the HT383 hydraulic roller that is a short 196/206 degrees of duration at 0.050-inch tappet lift. The short-block is fully dressed with front cover, oil pan, and counterbalanced harmonic damper. Finally, the pistons are a hypereutectic dish design to keep the compression in line. With this camshaft and the proper cylinder heads, the smog police will never be the wiser.
Now to keep everyone happy, check out Dart Heads for its Iron Eagle S/S small-block Chevy cylinder heads. These feature a 165cc intake runner, heart-shaped chambers to improve combustion efficiency, and machined valve cover rails to eliminate leaks, and it will accept both center-bolt and standard small-block valve covers, as well as screw-in rocker studs that won’t pull out. The heads are offered in various combustion chamber volumes (67, 72, and 76 cc) to tailor to your compression needs. They also are offered in both 1.94/1.50- and 2.02/1.60-inch valve options at no additional cost.
First, for a 350 build, we would recommend going with the PN 10021070A, a fully assembled 1.94/1.50-inch valve package with 1.250-inch springs and retainers and 72cc combustion chambers. With the flat-top ZZ4 partial short-block your compression ratio will come in right at 9.4- to 9.5:1. This will be perfect for premium unleaded fuel. For the 383 partial, with its dish pistons, go with the PN 10024365A heads, which feature the same valve and spring package but with 67cc combustion chambers. We’d have the heads surfaced 0.020 inch, which will reduce the combustion chambers down to 64 cc. This, in combination with the dished pistons, will yield a 9.1:1 compression ratio.
With these builds, all the components from your 305 will bolt right on. The inlet manifold, rockers, roller lifters, and pushrods will all be compatible with these buildups. If it was ours, we would upgrade the inlet manifold to an Edelbrock Performer PN 3706. This specific Performer features EGR provisions and the proper inlet manifold bolthole angle to match up with ’87-and-later iron cylinder heads. The four center manifold bolts are stood up at a 10-degree-steeper angle compared with earlier (’86-and-earlier) cylinder heads.
Finally, the ZZ4 camshaft (PN 10185071) would be a great addition to your ZZ4 partial short-block. It would also just get past the emissions test and give you great performance with the rest of the package. The camshaft specs out at 208/221 degrees of duration at 0.050-inch tappet lift, 0.474/0.510-inch max lift, and ground on 112 centers. It was designed for the 350 H.O. emissions package that was a retrofit engine assembly for both the carbureted 305-equipped Camaros and Monte Carlos. This made a great driving package in these cars. Unfortunately, this package has been discontinued or you could have dropped it right in, completely emissions legal.