Similar in Look, the Prototypes Vary in Performance by Design
By Mark Robinson
WATKINS GLEN, N.Y. – A new addition to the IMSA WeatherTech SportsCar Championship in 2021 that fans here at Watkins Glen International and watching from home are noticing is the emergence of the Le Mans Prototype 3 (LMP3) class.
Because of the similarity in look and size to their big brothers, the Le Mans Prototype 2 (LMP2) cars, it may be difficult to distinguish between an LMP2 and LMP3. They’re similar in weight, with the LMP2 just 22 pounds lighter than the LMP3 (2,068 pounds vs. 2,090) and similar in size (an LMP2 is a maximum of 187 inches long and 71-75 inches wide; an LMP3 is 183 inches long and a maximum of 75 inches wide).
The primary differences lie in engines, aerodynamics, chassis technology and brakes. All LMP2s use a bespoke Gibson Technology 4.2-liter, naturally aspirated flat-plane V-8 engine producing over 560 horsepower. LMP3s race with a production-based Nissan 5.6-liter naturally aspirated cross-plane V-8 that generates about 460 horsepower, or 18 percent less than the LMP2.
The LMP2 also generates more efficient downforce than the LMP3. The LMP2 uses a full carbon-fiber monocoque – or structural skin – while the LMP3 uses a combination of a carbon-fiber tub and a tubular steel roll structure. Last, the LMP2 is equipped with carbon brake rotors, which slow the car quicker than the steel rotors on an LMP3.
With those advantages, the LMP2 is significantly faster – by design, since the LMP3 is the entry-level gateway to IMSA prototype racing. At the season-opening Rolex 24 At Daytona, the best laps turned by an LMP2 were about 6.5 seconds quicker than the top LMP3, equating to nearly 10 mph in lap-average speed over the 3.56-mile Daytona International Speedway road course. The LMP2 car also had a 10-mph top speed advantage at Daytona.
“They’re obviously different in lap time, but behind the wheel driving it, feeling what it drives like, they’re actually pretty similar,” said Colin Braun in assessing the two prototypes. An IMSA competitor since he started at age 16 in 2005, Braun has amassed 18 race wins and claimed the 2014 and ‘15 WeatherTech Championship season titles in the Prototype Challenge class, a predecessor to the LMP2 and LMP3 classes.
Braun was a member of the winning LMP2 team at the 2020 Rolex 24 and co-driver in the No. 54 CORE autosport Ligier JS P320 when LMP3 made its WeatherTech Championship debut this year at the Rolex 24. Along with co-drivers Jon Bennett and George Kurtz, Braun won the LMP3 class at the Mobil 1 Twelve Hours of Sebring Presented by Advance Auto Parts in March.
“Everything is just sort of scaled down, I would say, in the LMP3 car,” Braun continued. “A bit less power, a bit less aero, very similar tire. Everything’s just a little bit less of a notch of performance. … But the feel of it is surprisingly similar.”
There are several ways to visually determine an LMP2 from an LMP3 – primarily based on the color coding IMSA sets for its classes. LMP2 cars feature blue backgrounds of the car number panels on the nose and each side of the car; on the mirrors and rear wing endplate; on the LED position-in-class lights on each side of the car; and with a blue “LMP2” decal affixed above the windscreen. Orange is the designation for LMP3 cars in the same locations.
Cameron Cassels is another driver experienced in both categories. He finished second in the 2019 LMP2 points, the same year he won the class at Sebring. From 2018 through 2020, he drove in the IMSA Prototype Challenge development series that uses LMP3 machines, winning the Masters class championship in 2018 and finishing sixth overall in 2019. Cassels drove the No. 38 Performance Tech Motorsport Ligier new-generation LMP3 at the Rolex 24 in January.
The 52-year-old was detailed in his assessment of the performance differences between the two prototypes.
“The (LMP2) really gets its power by wringing out the engine at relatively high RPM,” Cassels said. “The 4.2-liter Gibson engine power really peaks at 8,500 RPM, so you really want to run it out until just before the rev limiter engages.
“The LMP3 car, though, as impressive as it is, produces its power at a much lower RPM. The NISMO 5.6-liter engine definitely sounds more like an American V-8 engine with the low-end grunt. The sounds of the two engines are easy to spot with the LMP2s screaming by and the LMP3s roaring by, if you can imagine that.
“Aerodynamically, there is a notable difference in what the cars can do,” Cassels continued. “It can be a bit of a mindbender trusting the increased grip offered by the LMP2 with the downforce. Both cars rely on downforce to get around quickly; the LMP2 just has more of it. Mechanically, the LMP2 car feels much sharper to drive. Everything just happens a bit quicker, with quicker feedback, in the LMP2 car. Throttle response, steering inputs and braking all feel a bit more direct and precise.”
Cassels said the carbon brakes on the LMP2 are much more efficient at stopping the car quicker than with the LMP3’s steel rotors. The key, he added, is building heat in the LMP2’s brakes by pumping the pedal, “otherwise they are terrifyingly bad. … With no ABS in these prototypes, it is easy to lock up under braking if you just keep your foot mashed on the brake pedal.”
Oddly enough, noted Braun, the braking points heading into a corner aren’t much different.
“You arrive at the corner a bit slower (in the LMP3), the car doesn’t slow down quite as well, so you end up braking just about the same place as you do in the LMP2 cars,” Braun said. “The car doesn’t make as much grip coming off the corners but you’ve got a bit less horsepower, so you end up putting the throttle down in about the same place. It’s just ironic how similar a lot of the driving marks and apexes and brake points are.”
The most noticeable difference between the two prototypes, both drivers agreed, is when navigating traffic with the varying speeds of the five competition classes that will all be on track in the upcoming Sahlen’s Six Hours of The Glen.
“It makes multi-class racing a bit different in each car,” Cassels said. “The LMP2 easily made short work of getting around GT cars, while the LMP3 car takes more patience. It takes more time to plan on where you can use your advantage in an LMP3 to overtake a GT car, as they simply have more power than the LMP3 car.”
It also depends, Braun said, on who’s driving a car at the time – a seasoned pro or less experienced pilot – and at what point in a stint competing cars are on.
“I would say that’s probably the toughest thing in LMP3 because all of the DPi cars, all of the LMP2 cars are substantially faster than the LMP3 class,” Braun said. “Then you have the GTLM class, which depending on if you’re on fresh tires and they’re on older tires, you start to get this crossover of about the same lap times. Even old tires on an LMP3 car versus a top pro in a GTD car on new tires can be pretty darn similar in lap time.
“The P3 car is tough from that side because you’ve got to plan for the way you’re going to pass the GT traffic. But you’ve also got to factor in where the GTLM traffic fits in and letting the P2 and DPi guys by. I would say that’s probably harder from a driving standpoint. It’s sort of that mixed traffic management. You’ve got quite a few cars faster, quite a few cars slower and you’re just kind of right in the craziness.”
Regardless of the challenges, Cassels and Braun agree that adding the LMP3 class to the WeatherTech Championship was a good idea.
“In the end, both cars are incredible race cars with the LMP2 car a natural progressive step up from the LMP3 car,” said Cassels.
Braun amplified on that point.
“(LMP3) gives people an opportunity to make a jump into WeatherTech and not have to wrap their arms around such a fast prototype car,” Braun said. “You look at the lap times of the LMP2 cars and they’re not all that far off of the DPi cars. For some folks moving up and into WeatherTech racing, certainly I think (the LMP3 class is) more approachable or a little bit less intimidating to come in and get racing. On the flip side, I think it’s quite a nice class for performance from the money standpoint as well. It’s just a nice, good, balanced class.”