IMSA Makes “Manual” BoP Adjustments for Detroit

Photo: Mike Levitt/IMSA

IMSA has made “manual adjustments” to its Balance of Performance for next weekend’s Chevrolet Detroit Sports Car Classic, going outside of its parameters in an effort to reign in the competition, primarily in GTP.

Confirmed by IMSA President John Doonan in a media call on Thursday, IMSA’s technical committee has opted to not exclusively use its data-based five-race rolling average, which “hasn’t reacted fast enough” according to Doonan.

Porsche Penske Motorsport has been undefeated so far after four races in GTP, while BMW M Team RLL’s Dries Vanthoor has scored pole positions in every single race.

As a result, both the Porsche 963 and BMW M Hybrid V8 have seen increases in minimum weight and reductions in power, with the Acura ARX-06 and Cadillac V-Series.R both receiving the opposite treatment.

The Cadillac gets a considerable 29 kg weight break, while the Acura will be down by 22 kg in Detroit. This compares to a 11 kg weight increase for the Porsche and 2 kg of additional weight for the BMW.

In terms of power, Acura gains the most in first-stage power, getting a sizable 21 kW (28 hp) increase, with the Cadillac up by 11 kW (15 hp) compared to the recent round at WeatherTech Raceway Laguna Seca.

BMW, meanwhile, faces a whopping 27 kW (36 hp) reduction at the first stage, compared to a 5 kw (6.7 hp) cut for the Porsche.

Second stage power levels, at speeds over 200 km/h, are varied. Acura gets a 4.5 percent reduction, while BMW gets a 6.2 percent increase, Cadillac has a 2.1 percent increase and Porsche has a 3.3 percent reduction.

Second stage power, however, is not expected to play a significant role on the tight and twisty downtown Detroit street circuit.

The Aston Martin Valkyrie, meanwhile, sees the smallest changes in GTP, with the car remaining at a minimum weight of 1030 kg, along with a 1 kW (1.3 hp) power increase in first stage and 2.9 percent increase in second stage.

In the GTD ranks, weight changes have been made to seven of the nine GT3 models, along with power adjustments (at first and second stage) to all cars.

The biggest weight change in GTD comes with the Lamborghini Huracan GT3 EVO2, which loses 20 kg, while the Ferrari 296 GT3, for instance, sees an 8.1 percent decrease in maximum declared power at the first-stage.

Doonan said that IMSA has a “responsibility” to have “equal and fair competition.”

“All of these changes are based on a data-driven process,” he said. “In the end, we’ve had a rolling average process year to date and we’ve realized that rolling process hasn’t reacted fast enough in equal and fair competition.

“I think the race at WeatherTech Raceway Laguna Seca was evident given the fact it went green all the way.

“You want to do the right thing and make adjustments that are based on a process but also when things are somewhat diverging in terms of competition, when you’ve got a couple of cars outside the performance band, and a couple of cars below it on the low side, you want to bring everybody together.

“I think anybody that wants to see exciting competition would want, what we’re trying to do here in both GTP and GTD [Pro] as we head into Detroit.”

Doonan indicated that it hasn’t yet been determined if Detroit will be a one-off event in terms of manually adjusting the BoP, or whether it could happen again later in the season.

“What we did going into Detroit was still look at the rolling average, no doubt, but we’re also doing a ‘manual adjustment’ such that we take into account the percentage of deficit that we’ve seen, or the percentage of advantage we’ve seen on cars in both categories, prototype and GT,” he explained.

“We’ve addressed this with the manufacturers [in a call] this morning, we’ll let them know what the process looks like going forward.

“But in general, the overall process is really no different than what it was in ’24 in terms of correcting overall lap time. But when we see an instability in the BoP, we want to make adjustments such the competition is as tight as possible.”

John Dagys

John Dagys is the founder and Editor-in-Chief of Sportscar365. Dagys spent eight years as a motorsports correspondent for FOXSports.com and SPEED Channel and has contributed to numerous other motorsports publications worldwide. Contact John