502 Chevy Big Block Buildup - Gen VI Gorilla Engine: Part 1
Big Cubes Equal Big-Time Power
From the April, 2004 issue of Sport Truck
By Mike Finnegan
Photography by Mike Finnegan, Westech Performance Group
This is the deluxe 502/502...
This is the deluxe 502/502 package (minus the plug wires) after assembly and just before it was installed onto Westech's dyno. No, the trick electric water pump isn't part of the package. Wouldn't that be nice if it was?
It's a fact that the easiest and cheapest way to build monster horsepower and torque numbers is with a large-displacement V-8 engine. These days, you don't need an exotic and expensive engine combination, nor do you need a high-compression engine, to build big-time power. Pump gas-friendly powerplants are now reliably cranking out the ponies that were at one time reserved only for race engines running high-octane fuel, thanks to advancements in engine block and cylinder head design. Using proven large-displacement technology, which has been perfected since the early 1960s, will routinely yield the power you seek, especially when you rely upon the engineers at General Motors for the building blocks. With this in mind, we power fiends here at Sport Truck magazine took a brand-new GM Performance Parts 502-cid crate engine and proceeded to tweak, test, and add basic performance parts to the bone-stock engine until we were satisfied with the results. Then we let the dogs out, adding larger cylinder heads and a roots-type supercharger to the mix, ending up with an engine that made more power than we knew what to safely do with on 91 octane fuel. In this, the first installment of a three-part crate motor power building series, we'll gather up baseline dyno information on the engine in its stock configuration as well as perform the first round of basic modifications and test the results.
The Deluxe Package
GM's sixth-generation crate engines are available in various combinations and displacements, from 454 cid all the way up to 572 cid. Our deluxe ZZ502/502 crate motor came shipped with the short-block pre-assembled. The bottom end is impressive to say the least. The cast-iron block features 4.4460-inch Siamese bores that are stuffed with forged-aluminum pistons. Forged-steel connecting rods with 7/16-inch bolts push the pistons, and they swing on a 4-inch-stroke forged-steel crankshaft. The rotating assembly is held in place by four-bolt main bearing caps.
Westech Performance Group's resident engine guru and dyno cell technician, Steve Brul, assembled the top end of the engine with ease. The ZZ502/502 deluxe package breathes through a set of aluminum, rectangular-port cylinder heads. The heads (PN 12363390) feature large 2.25-inch stainless-steel intake valves and 1.88-inch stainless-steel exhaust valves. The valves have 11/32-inch stems, and the heads also come with high-performance valve springs, seals, caps, and keys. With a combustion chamber volume of 110 cc's, GM rates this package with a 9.6:1 compression ratio - perfect for the measly 91 octane fuel that we are forced to buy in California.
The rest of the high-performance package is just as impressive. An aluminum dual-plane intake manifold is teamed with a four-barrel Holley 850-cfm vacuum secondary carburetor. A reliable GM electronic high-energy ignition distributor with built-in coil provides the spark to 8mm shielded plug wires and #4 Rapid Fire spark plugs.
In its stock configuration, this motor performed way beyond our expectations and exceeded the numbers advertised by GM. On Westech Performance Group's Superflow dyno, the 502 maxed out with 534 hp at 5,500 rpm and 569.6 lb-ft torque at 4,100 rpm. The motor pulled extremely hard, never making less than 500 lb-ft torque from 2,500 rpm all the way up to 5,500 rpm. The numbers were good and left us with a positive outlook on the work that lay ahead.
Easy Does It
The first step in our master plan called for simple and easy modifications to the top end of the engine, where we knew a few extra ponies lay in wait. The first stop on our runaway horsepower train was to Comp Cams for a new roller valvetrain. The factory camshaft measured as follows: At 0.050 inches of lift, the intake valves peaked at 0.224 and the exhaust at 0.234; gross valve lift came in at 0.527 on the intake side and 0.544 on the exhaust side. This hydraulic cam offered a good compromise of driveability and power with a very smooth idle.
Comp Cam's answer to GM's cam choice came in the form of an Extreme Energy XR288HR hydraulic roller camshaft. This profile would really wake up our engine, while still maintaining a smooth idle and driveability, because the engine would still make enough vacuum at idle to operate a truck's power braking system. Another bonus with this camshaft is that there isn't any need to re-adjust the valve lash after installation because of the hydraulic roller lifters used. The XR288HR specs out like this: At 0.50 lifter rise, the intake has a duration of 0.236 and the exhaust, 0.242; gross valve lift occurs at 0.521 inch for the intake valves and 0.540 for the exhaust; and lobe centerline is 110 degrees.
Along with the cam change, the rest of the valvetrain received upgrades to reduce friction and increase durability. The stock stamped-steel rocker arms were tossed in the trash in favor of Comp Cam's Magnum 1.7-ratio roller rockers. The pushrods were also upgraded to 3/8-inch Comp Cams units, and a double-roller timing chain was also thrown into the mix.
Next, Brul buttoned up the engine with a new Edelbrock Performer RPM Air Gap intake manifold. This dual-plane design is perfect for a street engine and will help pump up the power from idle all the way to 6,500 rpm. The Air Gap design helps cool the intake charge by allowing air to circulate beneath the plenum when the truck is at cruising speeds.
To feed the rat with a precise amount of fuel, we chose a new Race Demon 850-cfm carburetor from Demon Carburetion. The Race Demon carb has several key features that make tuning much easier. First off, the metering blocks are built into the fuel bowls, which eliminates an extra set of gaskets and potential leaks. This makes changing the jets a clean and easy task.
Finally, an MSD Ignition system was installed to take control of lighting the fire within the 502. The Pro Billet distributor and 6BTM spark box offer great flexibility, precise and powerful spark, and the ability to upgrade and add external plug-and-play modules. In most cases, we would have chosen MSD's 6AL ignition box, but the BTM box offers a boost retard timing circuit that will be a critical and much-appreciated feature once we install the supercharger onto this engine.
1. Here, the motor is installed...
1. Here, the motor is installed onto the dyno. Westech Performance Group will typically dyno five to six engine's per week. Everything from mild small-blocks to blown and injected 1,000hp big-blocks routinely pass through the doors of the company's dyno cell.
2. Before the motor is fired...
2. Before the motor is fired up, Steve primes the oil pump using this trick tool from MSD. This is an easy way to ensure that the rotating assembly is well lubed upon start-up.
3. After we gathered our initial...
3. After we gathered our initial dyno numbers, Steve then removed all the probes, cables, and linkages from the motor and unbolted the valve covers and intake manifold to ready the motor for our parts swap. This is where things get really messy - and fun.
4. The Holley 850-cfm carburetor...
4. The Holley 850-cfm carburetor and single-plane intake manifold are first removed from the motor as one piece; no need to separate them since we are replacing both. They worked extremely well, but we knew we could find more power from a new intake manifold and carb.
5. Next, the CSI electric...
5. Next, the CSI electric water pump used for dyno-ing the motor is unbolted and removed. Westech uses this pump in conjunction with its dyno to precisely provide waterflow to whatever engine is being testing.
6. The factory stamped-steel...
6. The factory stamped-steel rocker arms are the next items to go. These rockers get the job done, but there are a few extra ponies to be had by running the more accurate roller rockers from Comp Cams.
7. The oil baffle is also...
7. The oil baffle is also unbolted and removed from the lifter valley. The baffle is used to control the oil flow and disperse it more evenly over the pushrods and lifters. This is a must on high-performance engines.
8. Next, the pushrods and...
8. Next, the pushrods and lifters are removed from the heads and set aside.
9. To swap out the camshaft...
9. To swap out the camshaft for our new Comp Cams unit, we must first remove the crankshaft dampener; This is accomplished using a puller. The puller is bolted to the end of the crankshaft, then it grabs the dampener and removes it when turned with a wrench.
10. On Generation VI blocks,...
10. On Generation VI blocks, the oil pan must be dropped downward in order to remove the front timing cover; this is because GM changed the design of the front timing cover and it now has a flange that mounts inside the front main seal. No problem; Steve just removes the oil pan bolts using an air ratchet.
11. After the timing cover...
11. After the timing cover is off, the timing chain set is unbolted and removed. We'll reuse it again when we reassemble the engine.
12. The cam button retainer...
12. The cam button retainer is also unbolted and removed. The cam button retainer is used to prevent cam walk, which is important in high-performance applications. Cam walk will create inaccurate valve timing, which is critical when making big power.
13. Finally, it's time to...
13. Finally, it's time to remove the camshaft. Steve carefully slid it out of the engine block and set it aside.
14. Here is the new Comp Cams...
14. Here is the new Comp Cams Xtreme Energy XR288HR roller camshaft. This cam will increase power across the board and give us that lumpy idle that we love to hear so much.
15. Prior to installing the...
15. Prior to installing the cam, Steve coated it with assembly lube to protect the lobes until the oil reaches them during the engine's initial start-up.
16. After inserting the camshaft...
16. After inserting the camshaft into the engine block, the cam retainer bolts are coated with red Loctite solution and installed. Loctite is used here because, once again, we don't want the bolts to come loose and have the cam "walk" on us at high rpm.
17. Next, the double roller...
17. Next, the double roller timing chain is reinstalled. The factory timing chain is fine for our application, so we just reused it.
18. Up top, new Comp Cams...
18. Up top, new Comp Cams lifters, pushrods, and roller rockers are installed. The full roller package from Comp Cams should be good for an extra 8-10 hp through its ability to reduce friction in the valvetrain. Less friction equals more power.
19. After the front timing...
19. After the front timing cover is reinstalled and the oil pan bolts are retightened, the crankshaft dampener is lubed with anti-seize lubricant. Should we ever have to remove the dampener again, we'll be happy we used the anti-seize lubricant.
20. The dampener is then installed...
20. The dampener is then installed using an impact wrench. The factory dampener does an adequate job of reducing crankshaft vibrations and keeping the bottom end balanced, so we opted to keep it stock.
21. Once the lifter valley...
21. Once the lifter valley baffle is reinstalled, the front and rear intake manifold seals are made using a healthy dose of high-temperature gasket sealant. Steve first test-fit the intake manifold and determined the gap between the manifold and block to be 1/4 inch. Then he lifted off the manifold and squeezed a 1/4-inch strip of sealant across the engine block for a perfect seal.
22. Then the new Edelbrock...
22. Then the new Edelbrock RPM Air Gap intake manifold is set in place. This manifold will make power from 1,500-6,500 rpm and by design, cool the intake charge for even more power.
23. The final step in installing...
23. The final step in installing the intake manifold is to torque the bolts down tight. By now, the gasket sealant was dry, so Steve cut away the excess under the intake manifold using a razor blade.
24. The new Comp Cams Magnum...
24. The new Comp Cams Magnum 1.7-ratio roller rockers are adjusted next. Steve sets them up with 0.024 clearance using a feeler gauge.
25. Back on the workbench,...
25. Back on the workbench, our new Race Demon 850-cfm carburetor gets a jet change prior to being installed onto the motor.
26. The new 850-cfm Race Demon...
26. The new 850-cfm Race Demon carburetor was then installed onto the manifold after an initial jet change on the workbench. Demon makes jetting its carbs a snap because the metering blocks are part of the bowls and come off with just four screws. This eliminates a couple extra gaskets and reduces the chance of the float bowls leaking later on.
27. Next, an MSD Pro Billet...
27. Next, an MSD Pro Billet distributor is installed into the engine block. We chose the MSD 6AL system because of its performance, flexibility, and features that make it an excellent street/strip ignition.
28. Then the plug wires and...
28. Then the plug wires and distributor cap are installed. While all of this was going on, a set of Westech's own polymer valve covers was installed onto the heads to aid in adjusting the valves during the dyno runs.
29. The completed engine assembly...
29. The completed engine assembly was now ready to be hooked up to the dyno. Beautiful, isn't it?
30. These probes check the...
30. These probes check the exhaust gas temperature while the engine is running on the dyno. They are an excellent way to judge the running condition of the engine and whether it's running rich or lean.
31. Running the engine on...
31. Running the engine on the dyno requires a tag-team effort. In the engine cell, John makes adjustments to the carburetor and ignition timing.
32. Meanwhile, Steve runs...
32. Meanwhile, Steve runs the dyno and monitors the motor. When all was done, our newly modified powerplant produced some impressive numbers. For the complete breakdown, check out the dyno table.
With these minor alterations to the top end of the engine, we were able to push the big Rat motor to build more than 570 hp and 620 lb-ft of torque. This was an increase of 37 hp and 52 lb-ft of torque over our baseline dyno testing. More importantly, though, the engine was now pumping out more torque across the board, with numbers more than 600 lb-ft from 3,800 rpm to 4,800 rpm. That's a whole bunch of punch that you'll feel in the seat of your pants when towing a load or merging onto the freeway.
|502-CID STOCK |
|CRATE MOTOR |
|RPM ||POWER ||TORQUE |
|3,000 ||323.5 ||566.3 |
|3,500 ||374.1 ||561.4 |
|4,000 ||432.7 ||568.2 |
|4,500 ||480.8 ||561.1 |
|5,000 ||520.1 ||546.4 |
|5,500 ||534.0 ||509.9 |
|Max Power = 534 hp @ 5,500 rpm |
|Max Torque = 569.6 lb-ft @ 4,100 rpm |
|502-CID MODIFIED |
|CRATE MOTOR |
|RPM ||POWER ||TORQUE |
|3,000 ||338.8 ||593.1 |
|3,500 ||392.9 ||589.6 |
|4,000 ||473.1 ||621.2 |
|4,500 ||522.7 ||610.1 |
|5,000 ||550.5 ||566.9 |
|5,500 ||571.8 ||546.1 |
|Max Power = 571 hp @ 5,500 rpm |
|Max Torque = 621.2 lb-ft @ 4,000 |