502 Chevy Big Block Buildup - Generation VI Gorilla Motor: Part 3
From the November, 2004 issue of Sport Truck
By Mike Finnegan
Photography by Mike Finnegan
This month, we bring our GM Performance Parts ZZ502 crate motor buildup to a close, with one last, final run at the dyno that ends with blistering performance, jaw-dropping dyno numbers, and a high-five to engine-builder Steve Brul. The first two installments of this series shed light on the easy-to-install bolt-on parts, which took us from a mild-mannered but healthy 530hp engine to a king-for-a-day-status 740hp brute. These numbers are nothing to sneeze at, and for a motor that can be built in a weekend for less than $12,000 and still run on 91-octane fuel, we feel that this combo was worth every penny. But we're horsepower junkies, and you know what that means: We can't leave well enough alone when we know that there is more power to be made, more bling-bling to be applied, and more fun to be had. With this "more power equals more fun" mantra ringing in our ears, we tore apart our perfectly good motor in preparation for its rebirth.
After the beast was in pieces, we ventured just a few miles south of Westech Performance Group's facility to see Ray Field, owner of Dougan's Racing Engines. Dougan's is a well-known and respected machine shop and engine-building facility that has performed surgery on a plethora of Gen. VI GM engines, so we felt confident it could help us out in short order.
The crew at Dougan's machined our engine block, opening up the bore size from 4.47 inches to 4.50 inches in preparation for a new set of JE blower pistons. We reused the 4-inch-stroke forged GMPP crankshaft after it received a complete balance and micropolish. We also reused the forged GMPP connecting rods after they were resized and fitted with 7/16-inch ARP bolts. The entire rotating assembly was also balanced and blueprinted.
The long-block was once again made complete with our Air Flow Research 315 CNC'd cylinder heads and a blower-specific grind camshaft from Comp Cams. To feed the hungry machine, we picked out a set of 950-cfm Holley HP-series carburetors, which were promptly bolted onto an 8-71 Weiand street supercharger.
Steve Brul, resident dyno king at Westech Performance Group, cleaned, measured, and assembled our new parts. He also lent his expert hand at tuning the engine once it was strapped onto the Superflow dyno so that we could squeeze every last ounce of power out of the engine on 91-octane fuel.
For more information on any of the parts used in this article, please contact the companies listed in the source box.
Axis of Power 1. After a...
Axis of Power
1. After a quick bath, and Magnaflux to check for stress cracks, Dougan's machined our Gen. VI engine block. The main caps were installed and the main bearing journals were line-honed. The cylinder bore size was increased from 4.47 inches to 4.50 inches. When combined with the stock forged GMPP 4-inch-stroke crankshaft and 6.135-inch connecting rods, this engine will end up with a displacement of 509 ci. By the way, this block has a deck height of 9.80 inches.
2a. According to GM, the stock...
2a. According to GM, the stock crankshaft will stay true in applications as high as 1,000 hp. After spinning the crank on the balancing machine with the dampener in place, we discovered that we'd need to drill and weld two of the weights in order to perfectly balance the crank.
3. Next, the connecting rods...
3. Next, the connecting rods were shot-peened and reconditioned to remove any sharp edges that could turn into stress points once the reciprocating assembly is assembled. These sharp edges would be the first places to crack under the stress of a blown application.
4a. The rods were then fitted...
4a. The rods were then fitted with new bolts. These 7/16-inch ARP rod bolts were pressed into the big end of the rod. The bolt threads were coated with assembly lube to ensure that the nuts were properly torqued in place.
5a. The connecting rod journals...
5a. The connecting rod journals were carefully measured using the Sunnen inside micrometer, and then ground to ensure roundness. Each rod was individually ground, and then corresponding rods were honed together.
Balancing Act 6a. Once both...
6a. Once both the big and small ends of the rods were deemed ready, the rods were cleaned and balanced. Each rod was weighed, and then the lightest rod was determined. The heavier rods were relieved of excess weight after a few seconds on the belt sander until each rod weighed exactly the same.
7. In order to accurately...
7. In order to accurately balance the rotating assembly, Dougan's weighed not only the pistons, but also the wristpins, ring package, and bearings.
8. Again, the lightest piston...
8. Again, the lightest piston was used for a reference point, and the rest were lightened, this time using a drill press. The bottom end of the engine is just about ready for assembly.
Hot Rods 9. There are two...
9. There are two distinct ways to attach the JE forged blower pistons onto our GM connecting rods. The first is to fit the rods with bronze bushings and then install floating wristpins. This is arguably the best way to accomplish this task because if the engine ever needs to be torn down again, the rods will easily be separated from the pistons. We are an optimistic bunch, so we chose the quicker route and used press-fit wristpins. This method of attachment requires the rest pins to be thoroughly cleaned. The rods and pistons were then set into this rod heater and once they were thoroughly cooked, the pins were tapped into place. The clearance between the piston bore and pin is minimal, so once the parts cool, the pins are locked into place while still rotating easily.
Checking the Flow 10a. Since...
Checking the Flow
10a. Since our Air Flow Research 315 CNC'd cylinder heads are fresh, Dougan's simply chucked them up in its machine and took a few thousandths of an inch off the deck surface to ensure it was straight. Out of the box, these heads are built with 119cc chambers, but AFR milled them to 110cc previously to get the engine's compression ratio back to 9.6:1. This means that there was little material left before we got into the combustion chamber, so this was a critical step. Dougan's also performed a new valve job to ensure a good seal between the valves and seats.
11a. Lastly, Dougan's checked...
11a. Lastly, Dougan's checked the valve springs to ensure that at the installed height, there was a correct amount of spring pressure present at the seat.
Preparation for War 12. Fresh...
Preparation for War
12. Fresh from the machine shop and ready for assembly, we toted everything back to Westech Performance Group to watch as Steve Brul carefully cleaned, measured, and bolted the engine back together. Before any work was performed, Steve deburred certain areas of the engine block with a grinding stone. These areas include casting flash in the lifter galley, the external block surface, and the inside edge of the oil pan rail.
13. The oil passages, lifter...
13. The oil passages, lifter bores, and cylinder bores were each cleaned thoroughly with an appropriate-sized wire-bristle brush to ensure that no metal shavings from the grinding wheel were left. These metal particles will immediately cycle through the oil system and may not be caught by the oil filter, causing severe damage to the bearing surfaces upon break-in.
14. The block was then washed...
14. The block was then washed out with a garden hose for several minutes and then blown-dry by an air nozzle and the shop's air compressor. To prevent rust from contaminating the block, oil was sprayed over the cylinder bores and lifter bores, and inside the block. We were now just about ready to assemble the bottom end.
Measure Twice, Build Once...
Measure Twice, Build Once
15a. Dura-Bond camshaft bearings are a no-brainer installation as long as you remember to line up the oil passage holes in the bearing and engine block. Steve used a small metal rod to align the passageways.
16. A new Comp Cams bumpstick...
16. A new Comp Cams bumpstick was called into play since this incarnation of our motor will include a supercharger. This blower-specific mechanical roller grind includes more lift and duration for the exhaust valves to aid in clearing the cylinders after the power stroke. The cam specs out as follows when installed on a 114-degree centerline: Duration at 0.050: 260 intake/266 exhaust Gross valve lift: 0.668 intake/0.678 exhaust Since this was a mechanical roller camshaft, we had to replace the stock metal gear on our MSD distributor with a carbon gear and set valve lash every so often to ensure the valve timing stays with spec.
17a. After double-checking...
17a. After double-checking the rod bearing and main bearing clearances, Steve lubed the crankshaft journals with Childs and Albert assembly lube and set it in place. The ARP bolts were coated in ARP lube and torqued in the main caps in three stages, finishing at 75 lb-ft. He also checked the crankshaft thrust clearance and found it to be 0.004.
18. Before we could install...
18. Before we could install the piston and rod assemblies in the block, we had to assemble the ring package. These JE file-to-fit piston rings were set up with 0.023 top ring end gap and 0.025 second ring end gap.