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Engines & Drivetrain
ZZ502 Big-Block Engines - Big-Block Bolt-Ons
The ZZ502 Is A Great Crate Engine, But It Can Be Even Better With Just A Few Upgrades.
Jul 1, 2010
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ZZ502 Big-Block Engines - Big-Block Bolt-Ons
One great part about the partially assembled GMPP ZZ502 "builder's kit" is that much of the hard stuff, like assembling the short-block, had already been done. The short-block ships with the oil pan in place, but we couldn't resist the urge to pull it off and check out the internals. This was especially easy since GM utilizes a one-piece, reusable oil pan gasket.
The Gen VI block features four-bolt mains and is filled with a 1053 forged steel, externally balanced 4-inch-stroke crank and forged, shot-peened steel connecting rods with 7/16-inch rod bolts. This stuff will easily hold up to a bit more power.
Reimann also worked over and opened up the intake and exhaust ports, as well as cleaned up the heads for better flow. When we took the reworked heads to get flow tested at Westech Performance, we found that the chamber size had increased to 117 cc. We suppose we could have milled the heads down to get that compression back, but the small gain in performance didn't justify the cost. Besides, did we mention how our gas in California sucks?
Tim Reimann did a valve job, opened up the bowls, back-cut the valves and short-turned the corners back to get better cross flow. He also took out the parting lines, and generally smoothed out any bumps or protrusions.
The 4.470-inch bores are filled with forged 9.6:1 aluminum slugs. The relatively low compression assures that this is a pump-gas-friendly mill, even in states where 91 octane pretends to be the good stuff.
When we said earlier that the ZZ502 kit from GMPP came with everything, we weren't exaggerating. Every seal, bolt, plug, and widget needed comes packaged in the crate. water pump, distributor, and plug wires.
Even supplies like pipe sealant, RTV, and assembly lube are included. The deluxe kit also includes accessories like the starter,
After lightly coating the supplied bolts with oil, we installed the now-ported GMPP oval port heads and torqued them per the GMPP instruction sheet.
One of the main keys to making more power was upping the size of the cam to a 242/248 duration, .566/.566 lift, 112 LSA COMP stick. Quite a bit larger than the 224/234 duration, 527/544 lift, 110 LSA cam that came in the engine from GM. This should generate more power while keeping the engine easy to live with on the street.
Using the GM-supplied assembly lube, we then dropped in the hydraulic lifters that came in the ZZ502 kit.
We then installed the lifter retention system and snapped the oil shield into the lifter valley. The oil shield keeps hot oil off of the bottom of the intake manifold. After this, we easily finished assembling the engine. Again, we were impressed at how everything needed-no matter how small-was included in the kit. GM really meant it when they called this kit "deluxe."
The easy and affordable solution to our valve cover clearance issue was found over at Spectre Performance in the form of these sweet fabricated aluminum pieces (PN 5041, $191.39). The 850 CFM Holley 4150 carb included in the ZZ502 kit has vacuum secondaries and an electric choke, which is ideal for street duty, and the Bow Tie intake is geared toward putting out gobs of low-end grunt.
This was also our first chance to try out COMP's new Ultra Pro Magnum rockers (PN 1620-16). We stuck with the same 1.7 ratio, but everything else about these new rockers are better than the stamped steel pieces included in the engine kit. Even though they are 8650 chrome-moly steel, they are still 5 percent lighter where it counts at the valve, compared to aluminum rockers. This is due to their web-like structure that adds strength where needed and reduces mass in low-stress areas.
Here's our finished and upgraded ZZ502 crate engine. The supplied aluminum Bow Tie dual-plane intake, Holley 850 CFM carb, harmonic damper, and HEI distributor top our long-block. Since our dyno uses an electric water pump, we didn't bother putting on the aluminum GM unit. We also found that the ZZ502 valve covers were just barely hitting our new COMP rockers. To clear, we would either have to double up the gasket or swap to a taller valve cover.
The ZZ502 is rated at 502 hp at 5,200 rpm and 567 lb-ft of torque at 4,200 rpm. After a little tuning, we nailed down 582 horses at 5,600 rpm and 594 lb-ft at 3,900. In addition to the gains of both torque and horsepower, we also liked how peak torque came on lower and how the 502 pulled farther than it did in stock form. Even if you account for some variance between GM's dyno and ours, that's a pretty decent gain.
Out of curiosity, we also decided to try a small 1-inch open spacer. Horsepower moved up a touch to 586 at 5,800 rpm while torque dropped to 589 lb-ft at 4,100 rpm. In essence, we traded a little low-end torque for a bit more horsepower on the top end. In a street car we would rather have the torque.
With both the Holley 1,000 CFM carb and the high-rise single-plane intake, we lost a ton of low-end power with almost no gain up top. The mill just wasn't able to hang in the upper rpm where a combo like this really comes on. But hey, it was worth a try. Considering the price of the carb and intake, the better "bang for the buck" is what GM supplied with the ZZ502 kit.
We then grabbed a Weiand single-plane high-rise intake off the shelf and slapped on a Holley 1,000 CFM carb. Before this we tried just the 1,000 CFM Holley carb (no spacer) on the GM intake and found almost no change with peaks of 588 hp and 595 lb-ft of torque.
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