IMSA Issues Prototype BoP Changes for Rolex 24
IMSA released Friday Balance of Performance (BoP) adjustments for the Prototype class in advance of next weekend’s TUDOR United SportsCar Championship season-opening Rolex 24 at Daytona.
The biggest change come with revised air restrictor sizes, which sees a reduction in power for Daytona Prototypes and clarifications for P2 cars, following data from the Roar Before the Rolex 24 as well as dyno testing performed earlier this month.
DPs will have roughly a five percent reduction in power, with the Chevy-powered entries now utilizing a 2.5 percent smaller air restrictor in diameter, and the Ford EcoBoost-powered Rileys running 33.1 mm openings.
Nissan-powered P2 cars have been confirmed with 41 mm sized restrictors (in diameter), while the turbocharged HPD engine will have two 31 mm openings.
Both are in line with IMSA’s proposed five-percent performance increase over the current ACO LMP2 regulations.
DPs led the way in testing at Daytona, with the quickest P2 car, the No. 1 Extreme Speed Motorsports HPD ARX-03b, ending up with a best time that was 1.2 seconds slower than Christian Fittipaldi’s 1:38.630 lap set in the No. 5 Action Express Corvette DP.
“Working with the engine builders, we took the engines to the dyno after the test. It helped us determine some of the other items we were looking at,” IMSA’s Scot Elkins told Sportscar365.
“The testing at the Roar enabled us to get the final adjustment of performance for the prototype class, which we published today.”
Fuel capacities for both platforms are now confirmed, with gasoline-powered P2s allowed to carry up to 72 liters, with DPs at 76 liters.
The clean diesel-powered Mazda SKYACTIV-D entries will be permitted 70 liters, while the DeltaWing will run at 48 liters, with also a 10 kg reduction in minimum weight.
Boost pressures were also defined for the turbocharged HPD, Ford and Elan-tuned DeltaWing powerplants.
“We had data from the Roar and we reduced the power of the DP cars, which should help the fuel mileage,” Elkins said. “We did a very slight increase in the DP fuel capacity, just to max out the fuel cell.
“To compensate for the difference in fuel economy, we’ve reduced the P2 [capacity]. To compensate the flow going to a smaller capacity, we also reduced the [refueling] restrictor to try and balance that as well.”
Elkins estimates the change in the refueling restrictors will result in 3-4 second quicker fuel fills compared to last year.
Minor adjustments were also made to the spec Prototype Challenge class, which will see a revised rear wing placement.
The Oreca FLM09′s Chevy-based powerplant had been hitting the rev limiter around Daytona, and while a taller gear was tested at the Roar, Elkins said it didn’t entirely solve the problem.
“We are just basically trying to [tweak] the aero setting and not let them have a setting under the “hole 6″ wing position on the car,” he said. “That will obviously induce drag and hopefully it will solve this rev limiter problem.”
Elkins said he expected BoP changes for GT Le Mans and GT Daytona to be released later tonight.