Indy power struggle

Senior Editor

Panther Racing's Tomas Enge pilots a Chevy-powered Dallara Racer.

Last race of the 2003 season, Texas Motor Speedway, Turn 3, lap 188 of 200: Team Rahal driver Kenny Brack, piloting a Honda-powered Dallara racer at about 220 mph, touches tires with the car driven by Tomas Scheckter. Brack's car goes airborne then slams into steel fencing above the retaining wall and disintegrates. Miraculously, Brack survives the 93-g crash but sustains multiple injuries, including a broken back.

Twenty-six-year old driver Tony Renna wasn't so lucky. His Toyota-powered Panoz G-Force car soared through catch fencing at the Indianapolis Motor Speedway during a private test, just 10 days after Brack's crash. Renna died from his injuries. An onboard Accident Data Recorder pegged the car's speed at 227 mph just before he lost control.

The two "flying" crashes prompted Indy Racing League officials to cut engine displacement from 3.5 to 3.0 liters (effective at the 2004 Indy 500), a move designed to trim speeds by about 10 mph. It worked. Buddy Rice in 2004 won the pole with a four-lap average speed of 222.024 mph, while Helio Castroneves did so at 231.725 mph the year before.

It's not the first time the IRL has stepped in to slow down the IndyCar racers. The current displacement cut is the third since 1997 when the IRL went to production-type normally aspirated 32-valve V8s "already in development by major automakers," according to the original Indy Racing League rulebook, eschewing the more exotic and powerful CART engines. Both engines burn methanol, though the turbocharged 2.65-liter Ford-Cosworth XFE CART V8s make about 750 hp versus roughly 600 hp for the 3.0-liter IRL engines. High horsepower isn't generally a problem for CART cars that compete mostly on road courses. But it tends to be overkill for cars run on superspeedways such as Indianapolis with long straightaways where speeds can easily get out of hand. Here, about 220 to 225 mph is considered "safe" for qualifying, while race speeds are typically 10 mph less.

HALLOWED HORSEPOWER
To meet IRL objectives, "We basically had to lose 100 hp," says GM Racing IRL Program Manager, Joe Negri. "We couldn't put enough drag in the car to get speeds down." In the CART engines, a calibrated pop-off valve limits turbo-boost pressure and power. The IRL instead imposes a strict rev limit that more or less has evolved with engine formula. For example, the 10,500-rpm rev limit set for earlier 4.0-liter engines resulted in excessive piston speeds, and was subsequently lowered to 10,000 rpm. The 3.5-liter engines as well saw a drop from 10,700 to 10,300 rpm as track speeds crept higher.

The IRL contemplated lowering the limit again (before making the 2004 displacement change). But the engines would have needed shorter-duration camshafts that retained the same high lift as the longer-duration camshafts of the higher-revving spec. The result: excessive camshaft accelerations that abuse valve-train components and shorten engine life, something the IRL tries to avoid in the interest of containing costs. IRL specs also fix engine bore diameter at 3.66 in. In Chevy's case, engine designers shortened stroke length by use of a different crankshaft, rods, and pistons.

The displacement change had Chevy playing catch-up with rival IRL engine suppliers Honda and Toyota. It was a Honda engine that powered every CART champion between 1996 and 2001. Before Honda, Ilmor Engineering Inc., Plymouth, Mich., built engines for seven of eight champions in the CART Champ Car World Series from 1987 to 1994. Honda and Ilmor joined forces in 2003 to campaign their IndyCar HI3R 3.5-liter engine and won two races and three poles. The following year the pair won 14 of 16 races with the HI4R 3.0-liter engine. Toyota won the other two.

"The racing business is cyclic," says Negri. "Chevy's latest-generation engine introduced at the end of 2003 won three of the last five races." Into 2004, it took GM a little bit to figure out the slower piston speed of the 3.0-liter design. But it did, and by the last race of 2004, I believe Chevy engines made the most power."

Besides stroke length, many of the design changes at Chevy involved the fuel-injection system. Engines run on methanol make more horsepower than gasoline burners, simply because they burn about twice the amount of fuel. The fuel's cooling effect also allows higher compression ratios without engine-damaging detonation. But "Engine power is extremely sensitive to injection geometry," Negri explains. "A 1° change to the angle at which you inject fuel can cost 10 hp. Things that may not have worked on earlier designs may work now."

IRL-mandated changes and the everencroaching competition keep engine designers hopping, though lately they have been especially busy. That's because Honda and Toyota in 2003 began leasing engines to IRL teams instead of selling them, a business model borrowed from CART. Chevy followed suit the next year.

Leasing lets engine builders control the spec and verify their engines are run properly, which boosts reliability and helps control costs. Chevy, for example, rebuilds its lease engines every 550 miles. "It's cheaper to disassemble and inspect the engines and replace a few parts than to risk running them longer," says Negri. Teams aren't permitted to make changes without approval of the engine builder. Moreover, teams can't buy an engine and give it to the competition to reverse engineer, an incentive for engine builders to give teams their best stuff.

Race engines are in a constant state of development. GM, for example, had 20 separate mechanicalrelated projects for the Indy 500 alone. Items are tested alone to see if they make power and then combined. Promising technology is installed on a test motor and run on a dynamometer for 500 miles to see if it lives. Then it goes in a car. At one point last year GM had 160 projects going on at once, some the result of testing or simulation, others from the ideas of individual team members.

Leasing helps level the playing field and relieves teams of the care, feeding, and development of finicky race engines, but it's the drivers who ultimately have to live with IRL rule changes. The 3.0-liter engines tend to have a narrower power band than their 3.5-liter predecessors, forcing drivers to shift more often. IRL engines are generally tuned for peak horsepower and have a narrow power band to begin with. Short tracks, street circuits, and road courses necessitate retuning to broaden the power band, at the expense of peak horsepower. At the Indy 500, drivers typically downshift a gear or two coming into turns off the straightaways as they enter the eighth-mile short chutes, while road courses such as Watkins Glen may require 60 to 70 shifts per lap.

KEEP THE PEDAL TO THE METAL
Once underway, race drivers typically don't use the clutch for shifting. They instead lift off the throttle momentarily to unload the transmission shifting dogs during upshifts, a process that takes 0.1 sec or more, time that the car is not accelerating. Conversely, drivers blip the throttle on downshifts to synchronize gear speeds. All of this can be tough on drivetrains, and there's always a chance for missed gears and engine-damaging overrevving.

Technology recently borrowed from CART called shift-without-lift gets around the problem. It lets drivers shift the transmission without letting up on the throttle. SWL dramatically cuts lap times by helping cars more quickly reach terminal speeds. Formula One race cars, for reference, also use SWL systems, but hydraulic and pneumatic actuators move the levers in response to movement of driver paddles on the steering wheel.

The six-speed sequential transmissions used in IRL race cars shift like a motorcycle. Drivers simply pull or push a mechanical shift lever to go up or down through the gears. The lever is fitted with strain gages that sense when a driver has committed to an upshift or downshift. In response, the Engine Control Unit (ECU) momentarily interrupts the ignition, fuel, or both to allow a shift. A good shift using the method takes about 30 to 60 msec, and teams constantly tweak the parameters to try and make it happen faster.

SWL helps avoid excursions above established rev limits, which at present, caps engine speed at 10,300 rpm. Fourth, fifth, and sixth gears are closely spaced to help drivers keep engines running as fast as possible without exceeding the rev limit. Still, the limiter can be triggered by a spike in engine speed from rear tires skipping over bumps on the track, when running in the draft behind another car, or from a tailwind. The tamperproof limiters track the number of excursions above 10,300 rpm then signal a cut to 9,500 rpm for a period of time. "The penalty is generally not enough to cost a race but does put a significant dent in performance," explains GM Racing Track Support Manager, Nick Lester, whose expertise is in engine-electronic controls. His job is helping teams that run Chevy engines get the most from them. "Teams try to avoid the limit at all costs but get as close as possible."

Of course, any time the IRL enacts rules to curb track speed, teams will find ways to regain it. Horsepower and revs aren't the only ways to limit top speed though they are arguably the most effective. There is talk that the IRL is looking at narrower, less "grippy" tires to slow cars and keep them on the ground. This year, more downforce from a revised aero package should help drop Indy 500 qualifying speeds below 220 mph, though engine suppliers have had a year to dial-in the smaller mills, and the 2.5-mile oval track has been resurfaced, so speeds could creep higher.

Horsepower Versus Indy 500 Pole Speed

1996 1997 1998 1999 2000 2001 2002 2003 2004 Note that sometimes track speeds increase with drops in engine displacement and horsepower, the result of ever-impressing chassis and aero packages, as well as better track surfaces. "Had nothing been done to cut power, speeds probably would have hit 240 mph by now," says GM Racing IRL Program Manager, Joe Negri.

MAKE CONTACT

GM Racing
www.gm.com/company/racing/index.jsp
Ilmor Engineering Inc.
www.ilmor.com
Indy Racing League
www.indycar.com