2007 Petit Le Mans Race - Atlanta Braved

Fresh Competition And An On-Track Dustup Can't Stop Corvette Racing At The 10th Annual Petit Le Mans

Dr. Greg Johnson Mar 1, 2008 0 Comment(s)
Vemp_0803_08_z 2007_petit_le_mans_race LS7R_engine 2/9

The Story Behind The LS7.R
By the late '90s, Herb Fishel and the rest of the GM Racing crew were ready to raise the Corvette banner at the legendary 24 Hours of Le Mans. But because GT-class rules required strict adherence to the specifications of the street-going model, structural modifications to the car would be severely limited.

Fortunately, there were other areas in which performance and durability improvements could be made. One of those areas was engine development. Corvette Racing partner Pratt & Miller went to Katech Engineering to help achieve their goals for the nascent race car's powerplant.

Katech had a long history of working with GM on other projects, so the new endeavor was a natural collaboration. According to John Rice, a GM engineer at the time, it all began with a "what if" scenario regarding the viability of entering a Corvette race car in Le Mans. That started the wheels turning, and by 1999, Corvette Racing had a C5 racer sporting a race-bred 6.0L LS6.

Katech massaged the powerplant as best it could to optimize performance and durability over the race's 24-hour duration. Still, Corvette Racing's debut at Le Mans that year was less than auspicious. At that time, the reigning force in the GT1 class was the Dodge Viper. With 8 liters of displacement and a couple of years experience competing at Le Mans, the Vipers were simply too strong for their crosstown rivals. For the following year, everyone at GM and Katech went back to the drawing board and concluded that a 7.0L configuration could give the Dodges a run for their money.

Despite their identical displacements, the racing and street versions of the LS7 have very little in common. After all, the production engine has to start consistently in subzero temperatures, keep its cool in stop-and-go traffic, and exhibit flawless driveability throughout its long service life. By contrast, the race motor is never started until fluid temperatures have reached 100 degrees (F), is hammered relentlessly at all times, and is designed to last for a finite time period-be it 24 hours at Le Mans or 2 1/2 hours on a street circuit like Detroit.

When the bare-block casting is received at Katech, technicians immediately cut off the bottom portion just beneath the crankshaft center line. This has the benefit of significantly lightening the engine-a fully dressed LS7.R weighs in at about 300 pounds-while also lowering the overall center of gravity of the race car.

The bottom sump cover, which is bolted to the crankcase, is then fitted with the lower halves of the crankshaft-bearing shells. Therefore, when the cover is bolted on the case, the bearings that the crankshaft rides on are also bolted in place. This makes checking bearing tolerances a little more difficult, but Katech personnel have mastered the art of reaching in through either end of the case to do the job.

To get as much power out of the race engine as possible, the engineers at Katech and GM have developed fuel/air mapping sequences that optimize each cylinder independently. Additionally, engineers can monitor in real time exactly what is going on in the engine while the car is on track. When the car comes in for a pit stop, the crew can plug into the car's computer-management system and change the mapping sequence if necessary. John Rice, now retired from GM and working for Katech, says the crew usually has three different mapping sequences to choose from at any given time.

Since taking on the sports-car racing scene with the C5-R/C6.R, Corvette Racing has established ALMS records for the most GT1-class race wins (C5-R: 31, C6.R: 24) and the most wins in any class (55). Astonishingly, the team has lofted the GT1 winner's trophy at Le Mans five times in the last seven years. With a track record like this, it's no wonder the LS7.R was named Global Motorsports Engine of the Year in 2006.


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