Crate engines have really made upgrading our Corvettes easy. Grab a keyboard or pick up a phone, if you roll old school, and in a few days a big ol’ crate will show up full of mechanical goodness. It couldn’t be any easier. The downside is that, compared to a custom engine, you may not get exactly what you want.
The good news is that your average crate engine from Chevrolet Performance can churn out more performance with just a few, relatively basic modifications. One example is their ZZ502 big-block offering. Out of the crate it puts out a respectable 502 horsepower and 567 lb-ft of torque. But it’s easily capable of more. The “basic” configuration (PN 12496963) comes completely assembled minus the intake, carb, water pump, and a few other bits. For this we decided to try their “deluxe” offering (PN 19291332) that included everything right down to spark plugs and wires.
We were curious what a couple of upgrades would do for the big-inch big-block in terms of power. Now, we didn’t want to mess with the short-block since it came fully assembled, but popping off and cleaning up the as-cast aluminum heads seemed like a logical place to grab a bit more power. We also thought the GM cam specs seemed a bit on the tame side, so sliding in a bigger camshaft was another easy path to better performance. We also decided to ditch the one part on the crate engine that we weren’t thrilled with, the stamped steel rockers. Swapping over to a roller rocker would increase power, reliability, and if we stuck with the same ratio we wouldn’t even have to buy new pushrods.
Topping the Z502 crate engine was a set of aluminum oval-port heads with 2.25 inch stainless intake valves. 1.88 Inch stainless exhaust valves, 290cc runner volume, and 110cc combustion chambers. Good heads, but like all as-cast cylinder heads they can benefit from a little massage therapy. For this we took then to Tim's Porting in Santa Clarita, California.
Tim Reimann did a valve job, opened up the bowls, back-cut the valves, and short-turned the corners back to get better crossflow. He also took out the parting lines, and generally smoothed out and any bumps or protrusions.
Tim also worked over and opened up the intake and exhaust ports. When we took the reworked heads to be flow tested at Westech Performance we found that the chamber size had increased to 117cc. We suppose that 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 bad our gas is in California.
01. The great thing about a crate engine is that all the hard stuff, like assembling the short-block, had already been done. The engine shipped 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 they utilized a one piece, reusable oil pan gasket. We also went ahead and pulled off the heads and timing cover.
02. The Gen VI block featured four-bolt mains and was filled with a 1053 forged-steel, externally balanced 4-inch crank and forged, shot-peened steel connecting rods with 7/16-inch rod bolts. These parts will easily suck up a few more horsepower.
03. The 4.470-inch bores were 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 is passed off as premium.
04. The newly worked-over heads were then reinstalled onto the ZZ502 short-block using new GM head gaskets (PN 12363411).
05. After lightly coating the supplied bolts with oil we torqued down the heads per the Chevrolet Performance specs in the instruction sheet.
06. One of the main keys to making more power was upping the size of the cam to a 242/248 duration, 0.566/0.566 lift, 112 LSA COMP stick. Quite a bit larger than the 224/234 duration, 0.527/0.544 lift, 110 LSA cam that came in engine from GM. The COMP cam should generate more power while keeping the engine easy to live with on the street.
07. Timing chains take a lot of abuse so we ditched the stocker and installed an adjustable version from COMP (PN 3110KT). The double-roller billet-steel piece featured a cam sprocket that can go 6 degrees (advance or retard) and the three-keyway crank sprocket adds another 4 degrees of adjustability. The chain came pre-stretched, heat-treated and the box included a Torrington roller thrust bearing for reduced friction.
08. Using generous amounts of GM assembly lube, we dropped the hydraulic lifters back into the engine.
09. To upgrade the valvetrain we decided to run COMP’s Ultra Pro Magnum rockers (PN 1620-16). We kept to the same 1.7 ratio, but everything else about these new rockers are better than the stamped steel pieces included with the engine. 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. They are also fully rebuildable, so they should be the last rockers this engine will ever need.
10. Next up was securing the lifter retention system and the “snap in” 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.
11. And here’s our reassembled and upgraded ZZ502 crate engine. Our long-block was topped with the supplied aluminum Bow Tie dual-plane intake, Holley 850-cfm carb, harmonic damper, and the GM aluminum HEI distributor. Since our dyno uses an electric water pump we didn’t bother putting on the aluminum GM unit that came with the engine. We found that the ZZ502 valve covers were just barely hitting our new COMP rockers.
12. The easy and affordable solution to our valve cover clearance issue was found in the form of some inexpensive aluminum fabricated pieces. We’re sure there are more streamlined choices out there, but these were handy and had more than enough clearance. The 850-cfm Holley 4150 carb included with the ZZ502 crate engine has vacuum secondaries and an electric choke, which makes it ideal for street duty and the Bow Tie intake is geared towards putting out gobs of low-end grunt.
13. The ZZ502 is rated at 502 horsepower 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 of torque 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 further than it did in stock form. Even if you factor in some variance between GM’s dyno and ours, that’s a pretty decent gain.
14. Out of curiosity we also decided to try a small, 1-inch open carb 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 and hood clearance.
15. 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 horsepower and 595 lb-ft of torque.
16. 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 crate engine.