Small-Block Chevy 5 Stage Build - Waking Up The ZZ4

Our greatest horsepower numbers were generated with the RHS Pro Action heads, Edelbrock Air Gap intake, and Mutha Thumpr camshaft.

The ZZ4 Story
When GM Performance Parts decided to create the archetypical crate motor, they didn't undertake the job lightly. In turnkey crate form, it features a four-bolt block, forged steel crank, 10:1 compression hypereutectic pistons, powdered-metal connecting rods, aluminum D-port cylinder heads, dual-plane intake, Holley 770-cfm vacuum-secondary carb, hydraulic roller cam (208/221 degrees duration at .050, .474/.510-inch lift), and HEI distributor. They build the ZZ4 for durability, and at a standard you'd expect of a production car engine. The strategy of being built for longevity and reliability has worked well for GM, however the ZZ4 is far from being "on the edge" of maximum performance. As we've demonstrated, there's a lot more potential lurking in the ZZ4. The five stages seen here are great for the ZZ4 owner who's ready for that next step, as well as someone considering a new motor. If you are considering a new ZZ4, you might want to consider a partial engine assembly, which leaves off the heads, intake, timing cover, water pump, HEI, camshaft, lifters, and carb. A quick look at the Jeg's catalog shows the partial ZZ4 assembly at $2,294.99 (PN 809-12561723) versus the complete turnkey ZZ4 at $4,849.99 (PN 809-12499712). That's a savings of $2,555. You'll still need the roller lifters, intake, carb (we used the dyno's higher priced 650-cfm Race Demon), ignition, timing gear, and water pump-figure about $1,250 for pieces comparable to the ZZ4's-and you've realized a net savings of about $1,300 over the turnkey ZZ4.

Stage 1
Peak Power: 360 hp
Increase: 16 hp
What We Did: Swapped the 1.50 ratio ZZ4 rockers for COMP Pro Magnum 1.52 rockers on the intake, put 1.60 ratio rockers on the exhaust, and swapped the stock pushrods for stronger Magnum pushrods. That's it. Stages 2-5 require both mods.

Stage 2
Peak Power: 399 hp
Increase: 55 hp
What We Did: Pulled out the ZZ4's hydraulic roller cam (208/221 duration at .050, .474/.510-inch lift), and substituted the smallest of the three COMP Thumpr cams. Removed the ZZ4 dual-plane intake and substituted an Edelbrock Air Gap. Removed the ZZ4's valvesprings and substituted COMP Beehive units. Rocker arms are still Pro Magnum 1.52/1.60 ratio units with Magnum pushrods.

Stage 3
Peak Power: 408 hp
Increase: 64 hp
What We Did: Pulled out the smallest Thumpr cam, and substituted the mid-sized Thumpr cam, which has longer duration. This was worth an additional 9 peak horsepower over the small Thumpr. This stage basically represents a camshaft comparison between the two different Thumpr cams, so the price remains the same.

Stage 4
Peak Power: 427 hp
Increase: 83 hp
What We Did: We chucked the ZZ4's aluminum heads, and bolted on a set of Racing Head Service cast-iron Pro Action heads with 2.02/1.60-inch valves, which come assembled from RHS with the same Beehive springs used in the previous two tests. The small Thumpr cam was put back in, so the easiest comparison of this test is with Stage 2, which shows the difference in cylinder heads. The result of the cylinder head swap (using the same cam as Stage 2) is a gain of 28 peak horsepower.

Stage 5
Peak Power: 436 hp
Increase: 92 hp
What We Did: Now it's time to throw everything in the mix. We pulled out the small Thumpr cam, and replaced it with the mid-size Thumpr, while leaving the RHS Pro Action heads and Air Gap intake in place. On the Pro Action heads, the middle Thumpr was worth 9 more peak horsepower over the baby Thumpr, which is no surprise because that's the same gain we saw when the cams were swapped on the stock ZZ4 heads. Overall, the mid-size Thumpr and the Pro Action heads were worth 92 more peak horsepower over the stock ZZ4, which was no slouch to start with. If you figure in the price of a new ZZ4 partial assembly (see sidebar) along with a comparable intake, carb, roller lifters, ignition, timing gear, and water pump, you'd have roughly $5,600 into this combo.