RET has charted the GM factory Corvette’s Le Mans GT engine adventure since the publication was launched in 2003. All those engines have been naturally aspirated. The years 1999-2004 saw the C5R GTS car use a Chevrolet LS1 90º bank angle pushrod V8 in 7.0 litre guise. Developed by GM in conjunction with Katech, that engine’s design and development was covered in RET 004 (Spring 2004) and RET 008 (May/June 2005).
Second and final appearance of the mid-engined Corvette C8.R at Le Mans in 2022
The 2005 GT1 Corvette C6R used instead an LS7, again in 7.0 litre guise and again co-developed with Katech. The design and development of that LS7R engine, which was used through to Le Mans 2009, were explored in RET 21 (March/April 2007) and RET 40 (August 2009), including the introduction of direct injection from 2008.
After Le Mans 2009, Corvette switched to GT2, initially (from August 2009) using a de-stroked 6.0 litre version of the LS7R as a stopgap measure, before a purpose-designed, 5.5 litre GT2 engine came on stream for the 2010 season. GT2 was destined to become the top GT category at Le Mans for that season, and was renamed GTE.
In RET 76 (February 2014) GM Powertrain’s GT project manager David Henninger remarked, “From the 7.0 litre GT1 engine to the 2010 5.5 litre GTE engine, basically the bore and stroke changed but the general configuration including the cylinder head stayed the same. Initially the GTE engine did not have direct injection since GM did not have the roadcar version of the LS7 engine with such technology, as necessary to qualify for its use in the class. Direct injection is new on the GT engine for 2014 following the introduction of an appropriate roadcar model.”
Where RET 76 explored the development of the 5.5 litre LS7-based GTE engine in port-injected guise, RET 82 (November 2014) looked at its direction injection development, including for Le Mans. RET 97 (September/October 2016) then carried the development story on through Le Mans 2015 and 2016, when a combination of direct and port injection was used.
RET 105 (September/October 2017) brought the story of the 5.5 litre V8 through to Le Mans 2017, after which it was much of the same through 2018 and 2019, only for a sea change to occur for the 2020 season. This was the arrival of the C8.R. Owing to the Covid pandemic, Corvette Racing was absent from Le Mans that year but it was back in 2021. Both of those years it raced the GT Le Mans (GTLM) class of the IMSA SportsCar Championship. For 2022 it committed to a full season in WEC, including Le Mans.
The C8.R is not an iteration of the C7.R but an evolutionary step forward. The car has been re-imagined from the ground up, with the engine now placed just rear of the driver, making it the first ever mid-engined Corvette. Powering the all-new contender is a brand new 5.5 litre naturally aspirated V8 featuring dual overhead camshafts and a flat-plane crankshaft.
The C8.R made its competitive debut in 2020 at the Daytona 24 hours, but only managed to come in fourth, with the sister car further down the order owing to an oil leak early in the race. Similarly, in the 2020 Sebring 12 hours, the team struggled to find the pace and came in fifth. Nevertheless, the team did go on to win the overall championship for IMSA GTLM in 2020.
2021 was a much more successful year for the team. The #3 and #4 cars achieved first and second respectively at 24 hours of Daytona, while at Le Mans the #63 Corvette came in second. That was significant achievement, considering it was the first outing at Le Mans for this new mid-engined competitor.
Corvette Racing managed to win the IMSA GTLM Championship again in 2021, giving two titles for the C8.R. For 2022, Corvette Racing decided to split the team into two, with one car running an entire season in IMSA in the new GTD Category and the other running in WEC in the GTE Pro category. This was Corvette C8.R’s first foray into a full season of the World Endurance Championship but it would also be its last.
That was due to the ACO announcing that the LM GTE Pro category would be scrapped in 2023, with GTE Am following suit in 2024. That meant this year was the last opportunity the Corvette CR.8 would have to win as a factory-backed team in the GTE Pro category at the 24 Hours of Le Mans. Corvette flew its sister car over from IMSA to enter the 90th running of the event as a two-car effort as usual. However, this year would be a race to forget.
The C8.R engine
The power unit in the C8.R is a completely different design from the engine in the C7.R. Down the hall from the production team at GM’s Powertrain Performance & Racing Center in Pontiac, Michigan, the Corvette Racing Team started designing the engine in parallel with its road-going counterparts.
“There was a lot of shared knowledge back and forth,” says Jason Socha, Corvette Racing’s engine program manager. “Obviously, we were racing this engine before the production engine was announced to the public. We were designing and racing while the production engine was being designed. There are a lot of similarities, and a lot of communication back and forth. Naturally it is based heavily on the production Corvette LT6 engine, sharing the same overall architecture.”
The Corvette C8.R was fast at Le Mans in 2022, but hopes of GTE Pro victory were dogged by bad luck during the race
This is the first engine to go DOHC since the 5.7 litre V8 in the C4 Corvette ZR1, dubbed the LT5 that was co-engineered with Lotus (which was not raced and is not to be confused with the supercharged LT5 in the C7).
“The last car [the C7.R] had a single cam, cam-in-block, pushrod engine,” Socha notes. “With the change to the dual overhead cams of the production car, the race engine followed suit. DOHCs have their pros and cons, but for a racing environment they have quite a few more benefits over the pushrod design. That’s why we moved to dual overhead cam.”
This is also the first Corvette GT race engine to feature a flat-plane crank, something more commonly found in European exotics than American V8s. The engine features a bore and stroke of 104.25 x 80 mm, with a compression ratio of 12.5:1, the same as the production LT6 engine. It retains the classic Small Block’s 4.4 in bore spacing but uses four valves per cylinder operated through finger cam followers. The 1.654 in (42 mm) titanium intake valves and 1.378 in sodium-filled exhaust valves are closed by dual steel coil springs.
While the C7.R switched to a combination of port and direct injection in 2017, the C8.R only has direct injection powered by two high-pressure fuel pumps. The pumps have also been upgraded to the latest Bosch spec HTP 6 over the previously installed HTP 5 on the C7.R. They also now sit in a new location.
“There were a couple of iterations in the C7.R, but on the current car, both of the pumps are in the valley of the engine,” Socha explains. “There’s a separate small, short camshaft that has lobes on it. It’s chain-driven all together, driving both fuel pumps.”
The LT6 has its block/crankcase extending to only the depth of the crankshaft axis. A lower crankcase/sump forms the main bearing caps and divides the crankcase into separate compartments. Unlike the production LT6 engine, the race engine uses a special aluminium alloy for the block, while both production and race head castings are in A356-T6.
“We use slightly different block material for improved heat transfer properties,” Socha says. “There is some use of that same material in other parts of the production engine as well.”
While fundamentally the same architecture, the team has made changes all around the engine. “We have the benefit here of a higher budget,” Socha notes. “So, basically we could take every component and make it a bit lighter and a bit stronger, things like that. There are bits and pieces that are shared between the two, but most of the components on it are specific to the race engine.”
A key aspect that is different between the C8.R and the road-going version is the packaging. “Packaging is very different between the two,” explains Socha. “In the racecars the engine sits a lot lower, so we had to do some work to get the engine lower in the car, shrinking the packaging a bit.”
GM’s racing propulsion manager, Ian Macewen adds, “The fuel cell, cooling system and oil tank are unique to the racecar. We had to maximise the amount of space for fuel, oil, and cooling, all the basic racecar-type stuff.”
While the production LT6 engine is capable of producing 670 bhp (500 kW) and revving up to 8600 rpm, the single 41.9 mm (nominal) mandatory intake air restrictor limits the C8.R’s engine to about 488 bhp and brings the redline down to 7400 rpm. “With the restrictor, you end up starting to hit the choke point quickly, so that's the highest race [engine] speed we end up running,” Socha says.
Corvette Racing is running one car in the entire 2022 WEC. This is it at Spa Francorchamps
Macewen adds, “The horsepower output really depends on the size of the restrictor we are required to run in any particular race. The production engine is capable of a much higher output and redline, so it gives us the freedom to move up or down quite easily.”
Between rebuilds, these race engines are run to around 3500 miles, a relatively conservative figure in endurance racing. “We run extremely conservative on ours,” says Socha, “Luckily, we have the ability to have very fresh engines all the time.” For this year’s Le Mans, the team installed a test engine for the Test day and a brand new race engine for the race weekend. Another spare fresh engine was also on hand.
Le Mans 2022
The two Corvettes started the weekend strongly, with both cars lining up at the front of the LM GTE Pro class. The #64 car took class pole with a time of 3:49.985, while the sister car set a time of 3:50.177. Alas, the #63 suffered left rear suspension failure in the early stages of the race and dropped down the order. It remained at the back of the GTE Pro pack until it was eventually retired owing to safety concerns.
Soon after, just before the 18-hour mark, the lead #64 was wiped out by two LM P2 cars passing by. Driven by Alexander Sims at the time, it had been leading GTE Pro by more than a minute, just before LM P2 car contact pitched it hard left into the guardrail nose-first.
Scrutineering for the Corvette’s last appearance at Le Mans as a pukka racecar, in 2022
“That isn’t how we wanted our Le Mans race to end,” says Laura Klauser, GM’s sportscar racing program manager. “We’re all proud of the dedication of everyone on the Corvette Racing team to give us the absolute best chance for our ninth class victory. We’re glad that Alexander is OK.”
With the announcement that current LM GTE Pro regulations are being scrapped next year, this was the last opportunity for Corvette Racing to hunt for a Le Mans win with the all-new C8.R. However, it was not meant to be; this Le Mans will certainly be one to forget for the team.
DATA SHEET
CORVETTE LT6 GTLM/GTE PRO 2022
90º V8
4.104 x 3.150 in = 334.96 cu in (104.25 x 80 mm = 5489.12 cc)
Naturally aspirated (single 41.9 mm intake air restrictor)
Ethanol fuel (bioethanol WEC/E10 IMSA GTD)
Aluminium alloy block and heads
Aluminium liners with nickel silicon carbide bore coating
Titanium con rods
Light alloy pistons, three rings
Five main bearings, plain
Steel crankshaft, four pins
Dual overhead camshafts, chain driven
Four valves per cylinder, one plug
Undisclosed included valve angle
1.654 in intake valves, 1.378 in exhausts
Distributorless ignition
Direct injection
Engine management system
12.5:1 compression ratio
Maximum rpm, 7400 (owing to restrictor)
SOME KEY SUPPLIERS
Heads: GM
Block/crankcase: GM
Crankshaft: Pankl
Timing drive components: GM
Finger followers: GM
Pistons: Pankl
Rings: Pankl
Piston pins: Pankl
Con rods: Pankl
Main bearings: GM
Rod bearings: Mahle Clevite
Fasteners: GM/ARP
Valves: Xceldyne
Valve springs: PSI
Gaskets: ElringKlinger
Ignition system: Bosch
Fuel injectors: Bosch
Engine management/data system: Bosch Motorsports
Water pumps: GM
Oil pumps: Dailey Engineering
Intake manifold: GM/Performance Design
Air filter: ITG
Fluid lines: Brown & Miller Racing Solutions
Wiring loom: GM
Heat exchangers: Mezzo
Fuel pumps: Bosch
Oil: Mobil