The process of building a race-ready GM DRCE Pro Stock engine
Contributed by Jeff Romack
There is an often heard yet undeniable maxim in NHRA Pro Stock racing that horsepower is king. Who could argue given that 40 cars separated by margins as razor-thin as .025 of a second compete for just 16 starting spots, meaning that each one percent gain or loss in power can be the difference between racing on Sunday or going home Saturday night.
To the casual observer sitting in the stands at any one of the NHRA POWERade tour's 23 national events, it all looks so methodical and very simple. Like a well-choreographed dance, a pair of Pro Stock Pontiac SC/T Grand Ams, both powered by naturally-aspirated, GM DRCE powerplants, pull up to the starting line, do their tire-smoking burnout's, back up, gingerly move forward into their starting posture, launch, and in less than 6.8 seconds, rocket down the quarter-mile reaching speeds in excess of 200 mph.
But things are not as simple as they appear. To get its 500 cubic-inch, 1,300 horsepower-producing powerplants race-ready for this fleeting moment on the race track, an engine shop must invest weeks of painstaking work, expend large amounts of capital, and pull together parts and commodities from numerous reliable resources in an effort to develop a winning piece.
"Excluding the cost of the race shop, you're still looking at an initial investment of approximately $750,000. In the dynamometer room alone you have about $250,000 invested and that includes expenditures for the dyno, the induction and exhaust units, and the water tanks."
After the fundamental materials and personnel are in place, the fun begins. Pawuk's engine department starts with a GM DRCE 500-cubic inch block and a set of GM DRCE cylinder heads. The block and the cylinder heads come raw, so prep time is needed to make the block and the heads race-ready. That includes machining the raw block, boring the cylinders, line bore of main and cam bearings, lightening of block, installing lifter bushings, decking the block, drilling of all bolt holes, grinding for connecting rod clearance, installing screens in valley of block, and honing cylinder walls and lifter bushings.
"When we receive the GM DRCE cylinder head castings, we start with approximately 75 pounds of raw aluminum casting," Pawuk said. "When the heads are complete, race-ready, they weigh approximately 53 pounds, so we're taking off approximately 20 pounds of aluminum per head."
Once the intake and exhaust ports, combustion chambers and all bolt holes including head, intake, exhaust and valve cover flanges, and rocker stands are installed, the head is then ready for the next phase of completion. That includes installing valve seats and valve guides, finishing the combustion chamber and intake and exhaust ports by hand, and the valve job.
"Depending on the deck height and bore-stroke combination, it takes about 16 weeks to get a new crankshaft," said Pawuk. "We also have to order connecting rods and pistons to meet our specifications, plus titanium intake and exhaust valves, camshafts, push rods, and intake manifolds.
"Obviously you need a set of carburetors, an oil pan, starter, timing cover and timing belt along with the gears for the belt for the crankshaft and the camshaft, lifter, rocker arms, valve covers, and basically a combination of all these different parts. By the time you put the whole program together with all of the parts coming in, you're looking at a minimum of a month, not including the crankshaft, and that's just for delivery of parts."
Now the block has to be honed which includes installing studs and bolting on a torque plate to the deck of the deck. This eliminates bore distortion. When the process is complete, everything is washed. After the parts are cleaned they go to the assembly room. Here the bearings are installed in the block including the main bearings for the crankshaft. Then the crankshaft and the camshaft are installed along with the timing belt. A piston is then placed in the block to check valve-to-piston clearance and also compression. The other seven pistons are matched and washed and the rings are fit to each cylinder bore.
Getting it together
Now the cylinder heads are assembled, including the valve springs, keepers and retainers. The head gaskets are punched out for water holes and installed onto the block. After the head gaskets are on, the cylinder heads go onto the block and are torqued to the proper specifications.
After the heads are bolted on, the lifters are installed into the bushings. Next come the push rods and rocker arms, and then the intake manifold is bolted on. The distributor goes in, the spark plugs and spark plug wires go in and both carburetors are installed on the intake manifold. Oil is poured into the tank, and all the push rods are checked for adequate lubrication and to make sure there is vacuum in the engines. That helps seal the rings better and adds horsepower.
"Ring seal is crucial," said Pawuk. "The more vacuum you can build in the crankcase the better ring seal you get and the more power you're going to make."
After going through some final checks, the engine is put on the dynamometer, warmed up and the timing checked. After another check of the engine, the dyno is cranked up to full power.
"It takes about three months to get one engine up and running, and then there's no guarantee it's going to be any good," said Pawuk. "The dyno allows us to run the engine so that we can establish a baseline for horsepower and determine where we need to be. After we run the engine on the dyno, we take it to the racetrack and see how it performs there. That's how we begin to build data, by knowing how the engine performs on the dyno, how the car performs on the race track and how far you may be off where you need to be.
"Finding adequate horsepower is a never-ending process. You have to keep inching forward or you'll fall miles behind. Not everything works. In fact about one percent of the things we do work and that's why our expenditures for research and development are so enormous, but you never know something's going to work until you try it."
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