Megajoules. Time. Energy usage. These are the new buzzwords for pit stops in the GTP class.

The time a GTP car is in the pits during the Rolex 24 At Daytona may not depend on how much time it takes to refuel the tank, nor change the tires, nor do a driver change. What will determine the time a car is stationary in the pits is how much energy the car has used in the previous stint, or how much it needs for the next.

IMSA has put a 920 megajoule cap on the energy that can be used during a stint. Exceed that, and the first penalty is a stop plus 100 seconds, increasing with subsequent violations. It’s no longer a matter of how much fuel the bladder can hold and when the fuel is low, it’s time to pit. Now the teams must pit before they use up their virtual energy bank, measured — as is the output to the wheels in order to make sure the 500kW maximum isn’t exceeded — by torque sensors on the halfshafts. And replenishing that energy bank is a matter of time, not fuel flow.

“It’s a virtual energy tank. (IMSA knows) how much power has been put to the car and therefore how much energy the car is using,” explains Brandon Fry, technical/race operations director at BMW M Team RLL. “So that will deplete over a stint. For here it’s capped at 920 megajoules. As we do each lap and burn that virtual energy, when we come in, we have to replenish that. So in many ways, what’s happened is the refilling of the car in the pit stop has been decoupled from the petrol fuel, and it’s based on this virtual energy. When we come in the car has to be connected to the fuel probe for a certain time to replenish this energy. Over the stint, if we burn all the virtual energy, it needs to be a 40-second stop. If it’s a half a stint, it would be a 20-second stop or whatever to replenish that virtual energy.”

It’s generally going to take longer to fill the virtual energy tank than it is for fuel to flow into the car. So the refueler may have stopped the fuel flowing into the car but has to keep it in contact so that the sensor recognizes it and the virtual energy counter continues to replenish. And if the car is taking on a full load of “energy,” the car is going to be stationary for longer than it takes to change tires or change driver.

There’s another layer of the pit stop procedure that didn’t exist in the pre-hybrid era: making sure the car is safe to touch. There’s a lot of high voltage moving between batteries and MGU, and if everything isn’t as isolated as it should be, it could be unsafe for a grounded crew member to touch the car. There are several systems in place to make sure it’s not an issue.

The addition of high voltage elements adds another element to pit procedures that GTP teams have to think about. Richard Dole/Lumen

“We do have to be aware of the car and the status it’s in,” reports Porsche Penske Motorsports Competition Director Travis Law. “There are various ways for us to do that. First, you’re going to notice the lights on the car at the A-pillar. Hopefully we stay green for the whole race, and that’s the first sign for anybody regarding isolation and if the car is safe, or not, to touch. So we’re always aware of that, the mechanics are always aware of that. On the timing stand we have telemetry that we can monitor isolation as well, so we’re seeing that live, the series is seeing that live. For a normal pit stop, hopefully you don’t notice much of a difference. That means we’re having a good day and the car’s running well, and everybody’s happy.”

A green light in that set of lights indicates the car is safe to touch. A red light, or no light, indicates it may not be. The teams say such a situation has been rare in running the cars so far. But if it arises, there is a procedure.

“The series has worked really well with the manufacturers to set up protocols that are the same across the board. And if the light is not green, we’re going to head to the (High Voltage) impound, which is HV, near pit in. And there we have protocols in place. You see us hauling around our totes full of the HV safety gear and the correct PPE. And then we’ll handle that car in the best way possible for the given circumstances that we have,” Law says.

For the fans, there should be little visual difference in most pit stops other than a little more stationary time than there might have been in the past. For the teams, though, it’s introducing a new way of thinking.