Two rounds into the 2023 IMSA WeatherTech SportsCar Championship, let’s address the elephant in the room: Balance of Performance matters.
That’s the most obvious takeaway after the recent 71st running of the Mobil 1 Twelve Hours of Sebring.
To refresh your memory, BoP is the tool used by sanctioning bodies including IMSA and the FIA to create parity between competitors. By mandating incremental adjustments to performance-related items including car weight, engine power, fuel consumption, and aerodynamics – sometimes on a race-by-race basis – the ultimate goal is to have all cars within a 0.5 percent window, expressed as 0.5s over a 100-second (1 minute, 40-second) lap. It’s especially effective in the GT classes, with multiple manufacturers fielding cars with front-, mid-, and rear-mounted engines in a variety of sizes and configurations.
At the Rolex 24 At Daytona International Speedway, the Mercedes-AMG GT3 was demonstrably the fastest car, with WeatherTech Racing claiming the GTD PRO class win in the No. 79 car, and the No. 32 Team Korthoff Motorsport and No. 57 Winward Racing entries showing class-leading speed in GTD. Aston Martin also enjoyed a highly successful race at Daytona, finishing one-two in GTD with The Heart of Racing’s No. 23 Vantage GT3 winning over Magnus Racing’s No. 44 counterpart.
At the other end of the spectrum, the brand-new Ferrari 296 GT3 and the 992-generation Porsche 911 GT3 were well off the pace, as was the BMW M4 GT3. To some extent, that was not surprising, as sanctioning bodies tend to take a cautious approach when setting BoP parameters for new cars. But several competitors, particularly from the Porsche camp, were vocal in expressing their displeasure with the baseline BoP for their new machinery.
Assessing the best Daytona lap time in race conditions for each marque, Porsche had reason for concern, with its best effort some 2.5 percent off the pace set by Mercedes-AMG. The Mercedes advantage was indeed considerable, with only Aston Martin coming within the 0.5-percent target window.
As a result, IMSA made some BoP changes prior to a two-day open test at Sebring International Raceway on February 15 and 16. After lap times and other data from those sessions were analyzed, additional BoP changes were implemented prior to the Sebring 12 Hours, as summarized in the chart below:
The most significant change was a 5mm increase in the Porsche’s air intake restrictor, intended to boost the 911 GT3’s horsepower and straightline speed. More air requires more fuel, so Porsche was also allotted an additional seven liters of capacity. Seven of the participating marques had their weight adjusted (five reductions, two increases) half received different fuel allotments, and Lamborghini also was granted a 1mm air restrictor increase.
The alterations appear to have been successful in tightening the competition, again based on best race lap times, with half of the competing marques within the 0.5 percent parity goal and all 10 bunched within one percent. Mercedes-AMG maintained a slim advantage over the Corvette C8.R GTD, perennially a strong performer at Sebring. Not surprisingly, Porsche made the biggest gains, moving from the slowest car to midpack; Ferrari was another to make a big jump, from seventh at Daytona to third at Sebring.
