The building block for great things. The ZZ4 short-block from GM Performance Parts is the
Walk down any row of the local car show and you will probably see a vehicle powered by General Motors' now venerable ZZ4 crate engine. The classic small-block ZZ4 is a quality built 350ci engine rated at 355 hp and 405 lb-ft of torque. To anyone looking for simple turnkey performance and a great building block for further power modifications, the ZZ4 has become the small-block Chevy of choice. Perhaps the best part of the ZZ4 is not simply its reasonably priced performance (a turnkey ZZ4 crate typically costs under $4,900), but its response to classic engine upgrades. Delivered with an aluminum dual-plane intake manifold, HEI distributor, 770-cfm vacuum-secondary carb, cast-iron water pump, damper, and flex plate, you just need to add fuel and air, then twist the key. But for the performance fan looking to really turn up the heat, there are a few things that can quickly garner almost 100 extra horsepower without a great deal of effort.
All of the tests were performed at COMP Cams' R&D center using a SuperFlow dyno. A range o
Setting the Stage
To test our theory about the responsive nature of the ZZ4 as a performance platform, we began by taking baseline dyno numbers on the engine. The 355hp rating and 405 lb-ft of torque are great street performance figures, but was that the real performance generated? Equipped with a Demon 650-cfm double-pumper carb (to free us of the vacuum secondaries) and 1 3/4-inch Super Comp headers, we pulled a few levers on the SuperFlow dyno, and read the charts.
After a number of adjustments for jetting and timing, our best numbers were 344 hp and 390 lb-ft of torque, a difference of 11 hp and 15 lb-ft of torque from the advertised numbers (which were spec'd with the larger 770-cfm crate motor carb). For the purpose of comparison, we will use these figures to determine the power gains from our component changes.
The various stages to be outlined here build greater horsepower by adding a specific combination of performance parts. Stage 1 is a mandatory stage for the build of our ZZ4. All other stages require that this stage be completed before the others are performed. While other stages can be selected independently (i.e., you can go right to Stage 5 and add both the cam and heads without completing stages 2-4), that is not the case with Stage 1.
To improve the basic platform, we scrutinized the parts most often considered the weakest links in terms of lost engine power and durability. Pushrods are always suspect, and in the case of our engine, we knew from previous testing that the factory units were weak, which results in a quick loss of full cam lift due to pushrod flex. To fix the problem, we installed COMP Magnum pushrods. These one-piece pushrods feature .080-inch wall chrome-moly steel tubing, and are heat-treated for added strength. A COMP pushrod length checker was used to ensure we had the correct length for our application.
Stage 1 of the ZZ4's upgrade program is the installation of Pro Magnum rockers and Magnum
Our second step was to change to COMP Pro Magnum rocker arms. These rockers are made from 8650 chrome-moly steel, and feature lightweight construction with a full roller design and roller tip. We replaced the factory 1.5:1 rocker arms and tested the engine with the new parts in place. The result: 16 additional horsepower and 10 additional lb-ft of torque.
As part of our experimentation process, we also tested the engine with different ratio Pro Magnum rockers. We installed the 1.52:1 ratio exhaust Pro Magnum rockers and 1.6:1 ratio for the intake valves. It should be noted that the 1.52:1 ratio rockers are COMP's stock replacement ratio; a slight ratio increase from the factory SBC 1.5 ratio has been proven by COMP engineers to improve performance and reliability without any negative side effects. The result is a total of 20 hp and 15 lb-ft of torque over the stock figures. The use of the 1.6:1 rocker arms on the exhaust side was considered, but after measuring for coil bind, it was determined that this would not be acceptable for our street-driven engine.
The swap to the Pro Action cast-iron cylinder heads delivered the greatest horsepower incr
Pick A Stage
Stages 2-5 all build power over the level achieved in Stage 1. The only other component change beyond the parts listed below was the installation of a higher-flowing Edelbrock Air Gap intake, which was done to take full advantage of the camshaft's increased flow. The 650-cfm Demon carburetor was also retained, although some jetting was required to optimize the performance of the engine.
Stage 2 features an obvious and typical engine-builder upgrade: the installation of a COMP cam. Our choice for this engine was a Thumpr camshaft. This new line of COMP hydraulic roller cams uses cutting-edge camshaft technology to deliver both great performance and excellent sound from the ZZ4. We're no strangers to the Thumpr cam line. You might recall that we dropped a Big Mutha Thumpr (the largest in the lineup) into our 496-inch big-block Chevy two months ago. These specially designed camshafts feature a combination of early exhaust valve opening, long exhaust duration, and a generous amount of overlap. The installation is a simple drop-in procedure, requiring COMP hydraulic roller lifters, which slip into the stock lifter bores without modification to the bore or the lifter.
For Stages 2-5, two different Thumpr camshafts were used: the Thumpr, and the Mutha Thumpr
A key to making this swap is the installation of COMP Beehive valvesprings and retainers. These springs are specially built to work with the Thumpr cam's aggressive lobe design, and they deliver great performance with lower-than-usual seat pressure and extended durability. The steel retainers used in this test were an added bonus, their reduced mass makes them comparable in mass to titanium retainers on a standard diameter valvespring. It should be noted that these springs were used for both of the cylinder heads used in Stages 4 and 5.
In Spintron testing, Beehive springs have proven to deliver a host of performance and durability improvements, not the least of which include reduced valvetrain weight and increased valvetrain stability. These single-coil, ovate wire springs feature reduced spring seat pressure for better valve control. Additionally, they retain durability for on-street driving, and can also handle more rpm and aggressive cam profiles (up to approximately .600-inch lift) for racing conditions.
The ZZ4 long-block was untouched during our procedure, with the exception of the installat
Thumpr Cam Considerations
The Thumpr hydraulic roller cam series from COMP represents state-of-the-art technology with regard to camshaft lobe design and overall timing. But there are a few more things worth considering for your specific vehicle combination. When using the Thumpr camshafts, especially the larger Mutha Thumpr (PN 12-601-8), it's recommended that a 3.55:1 ratio rear gearing and 2,800-plus rpm stall converter be employed to help off-the-line acceleration. With the basic Thumpr Cam (PN 12-600-8), a 2,500-plus rpm stall converter is a good idea. Remember that these camshafts will not pull as much vacuum as stock-style camshafts, so if you are running power brakes, check that you have a minimum of 16 inches of vacuum at idle, or the power assist may not function properly-a rude awakening if they fail when you need them most. On Hunkins' 496-inch big-block Chevelle, which has the Big Mutha Thumpr (same duration specs as the SBC, but with .570/.554-inch lift), there's only 7 inches of vacuum at idle at 900 rpm, but it has manual brakes. A change to the carburetor's power valve may also be necessary if idle vacuum is at or below 7 inches.