In sprint racing, the strategy is simple: Start as far forward as you can and improve your position from there until the checkered flag waves.
In endurance racing, there are a lot more factors in play, and someone on the team needs to put them all together to form a comprehensive strategy the whole team understands. Everything from pit stops and driver changes to tire changes and fueling strategies come into play — especially when the checkered flag is 25 hours away.
At the 2021 25 Hours of Thunderhill Presented by Hawk Performance, one team’s refueling strategy will be far different from that of all other teams. That’s because they’re taking on the longest closed-course endurance race in North America in a pure-electric racecar, with a proprietary powertrain, chassis and body developed by Entropy Racing in Sacramento, Pa.
It’s the first electric car ever to be entered in the event.
Team EVSR has developed a car and strategy that allows for “hot-swapping” batteries during a pit stop. The team can perform the battery swap in as little as one minute, 30 seconds. That efficiency is critical, because the team will need to perform battery swaps about every 44 miles, which the team has calculated to occur every 30 to 35 minutes at Thunderhill.
“A lot of the trick for us is getting the programming right, and the power consumption, so that we can balance our range versus our pit stop needs,” said team owner Charlie Greenhaus.
To swap the batteries, the team lifts the entire body off the chassis, which exposes all its systems, including the lithium iron phosphate batteries. They then lift the chassis independent of the batteries, which disconnects the power source from the car. Weighing in at about 1,850 pounds — about 700 of which is batteries — the car is tuned to produce about 130 to 140 horsepower.
“So, when we have it geared right, and everything is working properly, the car just continues to accelerate and push harder and harder and harder up to probably about a 100, 115, where it softens up a little bit,” Greenhaus said. “When we’re running a normal, full race pace without programming, we’ll see close to 130 mph at some courses. Our peak recorded speed is 140.”
The team has used Pikes Peak and the Mount Washington hill climbs and other endurance races to test and refine the chassis, powertrain and pit work. By going with lithium iron phosphate, an established technology used in the aircraft industry because of its stability, the team can avoid some the volatility of more modern materials like lithium ion.
“There’s very little free lithium. A runaway reaction on them basically generates enough heat to conceivably melt the plastic and set the plastic on fire, but can be extinguished with minimal amounts of water,” Greenhaus said. “In all the years we’ve been doing this, we’ve vented two batteries, and we had one, what I would call significant, but inconsequential fire at Watkins Glen, which was put out with three gallons of water. And that was when we were testing a power increase of about 60 percent over what we normally run.”
The electric car uses a bit of custom winding work done by Entropy Racing, but most of the components are off-the-shelf stuff. The team worked with EV West, a supplier in Covina, Calif., that makes powertrain components and conversion kits for gasoline-powered cars, to help develop the car.
Four drivers are going to split driving duties for the 25 hour event, which takes place Dec. 3-5, 2021. A crew of approximately 20 people will be on hand to look after the car.
“From the beginning, our concept was not to, you know, wave our arms and scream “environmental,” although we definitely have that bent here in the shop,” Greenhaus said. “But the bigger thing was to prove viability, to prove that we could go out and line up with everybody else and to show up and practice and qualify and race.”
