The situation facing GM Racing was unusual. Its Aurora V8 had won all but two Indy Racing League (IRL) events since the series began in 1997, but its identification with Oldsmobile, the nearly dead division, posed a growing problem the closer the division came to its termination date. This dilemma left the group with two options: depart the series at the end of 2002 with an unassailable lead, or regroup in 2003 under another banner.
It did neither. Instead, GM Racing put the Olds brand on the racing shelf a year early, and replaced it with the Chevy bow tie. Then it produced a new engine around the Aurora’s familiar Premium Racing V architecture, but sized and stressed from the start for life as a 3.5-liter motor with a “flat” (180°) crankshaft. This despite the fact that new engine rules–and therefore new engine designs–will arrive in 2003.
The IRL debuted in 1997 with a mandate for four-valve per cylinder, four-cam 4.0-liter V8s based around a production architecture. In time, the 10,500 rpm rev limit was reduced to 10,000 rpm, then raised to 10,700 rpm when the IRL lowered displacement to 3.5-liters. Later still, the IRL gave the competitors the option of running a 180° crankshaft in place of the production-oriented 90° crank so its single-seater series would sound like proper racers and not open-wheel stock cars.
“When the IRL put its rule package together, the bore center distance, cam drive (belt or chain), and other items had to be derived from the manufacturer’s production 4.0-liter V8, multi-valve engine,” says Roger Allen, chief engineer, Chevy Indy V8. Also set in stone were the cylinder bore diameter, the block’s minimum deck height, and the minimum distance from the crank centerline to the sump. Along with a standardized set of mounting points, these items remain unchanged through 2002.
“We didn’t have to start over with a clean sheet design,” says Allen, “which meant we could work on those things that remained from the original 4.0-liter formula.” In other words, though many of the parameters are common with the original design, the new engine–and Allen stresses that this engine is new–could be designed as a 3.5-liter engine from the start, which allowed a reduction in the center of gravity, weight, and reciprocating mass. “Only two parts–the oil and water pump assemblies–are carried over,” says Allen. “We didn’t see an opportunity to get an improvement from changing these parts."
After years of running the same basic package, the original design team had disbanded and moved on to other projects. Allen had to reassemble his small design team, and hire draftsmen and analysis personnel. He’s the only full-time GM employee involved in the design of the engine.
“One advantage we had was that we were able to incorporate the latest design and analysis tools for computational fluid dynamics (CFD), computer simulation of the entire engine, and finite element analysis (FEA). A lot has changed since 1996, and many of the things we used to do on a mainframe computer, we now do on a desktop system.” Some of the modeling involved studying how the aluminum alloy used to produce the block and heads flowed into the mold and hardened. According to Allen, “This was critical to eliminating voids, and making certain the part forms and cools in the proper sequence. We can’t build 1,000 prove-out parts like a production program can because we can’t waste the time or the money.”
What About Production?
Ask him to compare this to a typical production program, including whether or not the lessons learned are applicable to high-volume projects, and Allen smiles before answering. “Even though I’m sure we could use our short development process to speed up what we currently have in place for production designs, the risk we take is many magnitudes higher than we’re willing to take on a production engine,” he says. Gut feelings about what will or won’t work have no place in the production realm, where a mistake can cost billions of dollars. In racing, however, the loss is–at most–a few million dollars, slight embarrassment, and may mean nothing more than reverting to “the Aurora motor with a Chevy badge if the new one doesn’t work.”
Allen is quick to point out that a production engine costs less than one cylinder head on his latest creations. Therefore, losing $5/piston means nothing when you consider that Allen’s cost is spread over eight cylinders per engine and a total of 100 engines. “There’s no production-based manager who is going to look at what we do and say, ‘Yeah, I’ll use that’,” he says. “He’s actually more than likely to say something like, ‘You do what?’ instead.”
This doesn’t mean racing and production can’t learn from each other. Theories can be tested, development ideas shared, and concepts debated, but there are few, if any, one-to-one swaps between the two disciplines.
“One area we excel is in building complete engines to test the options that all of the simulations have produced,” says Allen. “With our system, I can get done in a couple of months what the production side takes years to accomplish. This comes out of having to find simpler, more direct ways of doing things to meet the constant time pressures. I’m not saying you shouldn’t do 3-D modeling,” he stresses, “but by quickly producing a 2-D model, taking that to a pattern maker, and having a test engine built you get the answer about which option to pursue that much faster.” And faster is the name of the game.
The IRL’s restrictive rules package not only keeps costs down by reducing the differentiation between engine and chassis packages, it leaves a very small development window for teams to crawl through. The result has been closely bunched fields and hard-fought races. “The races often come down to side-by-side dashes during the last laps of the race,” says Allen. “The guy with the most high-end horsepower wins. So we biased the power curve to the end of the rpm band.” That dovetailed nicely with Allen’s plans for reducing the engine’s weight, center of gravity, and reciprocating mass.
Sizing the engine for its current displacement meant that the crankshaft lost four pounds, and could ride on smaller bearing journals. This greatly reduced reciprocating mass and reduced friction. Each piston now weighs 330 g. and bore shrouding has been reduced in the combustion chamber to improve intake air flow. Each intake port is 2.75 in2 at the port opening, and the combustion chamber shape–cast into the piston crown–has been improved. Allen also increased the section between the valve pocket and the top ring land.
Intake valve weight has dropped from 44 g to 37 g, while the exhaust valves weigh 33 g each versus 42 g in the Aurora V8. This was accomplished by shortening the valves and decreasing their diameter. In addition, the larger diameter intake bucket is 8-g lighter at 35 g, while the exhaust bucket now weighs 31 g, a reduction of 9 g. High center of gravity components have shed 7 lb., while overall engine weight has dropped by 11 lb.
Other changes include redesigning the water jackets in the heads to improve cooling and reduce cracking in high-mileage (1,500-mile) engines, moving from chrome-plated titanium valve retainers to steel items, and redirecting the flow through the cylinder heads. All of the water in the engine now exits on the left-hand side of the front cover assembly since competitors have moved to a single water radiator in the left sidepod. This eliminates the pipe and clamps beneath the driver’s seat used ever since the teams abandoned dual water radiators.
Allen also redesigned the intake manifold assembly. The fuel pressure regulator atop it is now mounted in rubber to reduce reliability, and the fuel line mountings revised. The latter reduced the weight of the fuel line by one pound. Even the airbox received the once-over. The new design improves pressure distribution and improves access to the throttle position sensor.
The result is 30 more hp, greater torque, and less weight. Allen worked closely with suppliers to produce new parts for this engine, drawing heavily on their design and development expertise. “We went out and interviewed all of the major suppliers, and made a decision about who we wanted to support,” he says. “Other manufacturers have rod designers. We have Carillo. They have piston designers. We have JE. Where there was no competitive advantage in developing the part on our own, we relied on suppliers. The result is that our staff at GM Racing is small, but we can call on resources and expertise far beyond our relative size.”
Perhaps that’s the best lesson to be gained from this endeavor. It has allowed GM Racing to stay lean, cover a lot of area, and develop components and systems quickly and efficiently. As a result, Chevy’s Indy V8 has met its initial durability targets, and is undergoing preliminary track testing. And the engine for the revised 2003 regulations is well underway.