IMSA: Roar Before the 24 BoP issued

IMSA: Roar Before the 24 BoP issued


IMSA: Roar Before the 24 BoP issued


IMSA distributed its first Balance of Performance table for the new WeatherTech SportsCar Championship season late Friday, and it will be used to gather data during the Jan. 6-8 Roar Before the 24 test at Daytona International Speedway.

With the information captured during the three-day Roar event, IMSA will solidify the BoP heading into the season-opening Rolex 24 at Daytona race Jan. 28-29. In addition to assessing the relative performance between cars in the Prototype, GT Le Mans and GT Daytona classes, IMSA will also use the data to review and set its preferred lap time gap between those three categories and the spec PC class.

In Prototype, a 100 percent change in the cars that represent IMSA’s top class has led to all-new BoP tables to bring the IMSA-specific Daytona Prototype internationals and the spec World Endurance Championship P2s together on equal footing.

The lighter, faster DPis and WEC P2s replace the former Daytona Prototypes and 2015-era P2s, and with the total overhaul, the first item of note is the uniform minimum weight figure of 930 kilos (2050 pounds). For the 2016 Rolex 24 race, minimum weights varied from 530 kgs (DeltaWing DWC13) to 880 (BR01-Nissan P2) to 900 (Mazda P2 Prototypes) to 1039 (all Daytona Prototypes).

Only the new Cadillac DPi-V.R (pictured), and its massive naturally-aspirated 6.2-liter V8 engine, will use air restrictors (two with 31.9 mm diameter openings). The turbocharged engines found in the other two DPi models will, at least to start, have power figures manipulated without air restrictors.

To do so, IMSA has added a new BoP tool for Prototype this year, and it is specifically reserved for the DPis. Lamba figures (air-fuel ratio) have been set, with the mighty Cadillac motor (0.92) expected to run leaner than the Mazda RT24-P (0.88) and the Nissan Onroak DPi (0.85).

With less fuel making it to the Cadillac’s combustion chamber and the most being burned by the turbo Nissan, IMSA is using Lambda readings to refine power output across its DPi manufacturers rather than rely solely on air restrictors, which have demonstrated some shortcomings on turbo motors.

Initial fuel cell capacities have been set at 75 liters for all cars at the Roar, and with IMSA’s new refueling tank monitoring systems added in, the series will have plenty of info to determine the final refueling flow speeds and fuel consumption rates to make tweaks prior to the race.

Mazda’s 2.0-liter single-turbo inline-four powerplant has received more boost at some points in its rev range than its predecessor was given for the 2016 race, but has also seen a reduction at other points on the way to its 8900 rpm redline. Nissan, with its 3.8-liter twin-turbo V6 making its first appearance in IMSA, has a boost curve that looks similar to the one used last year by Honda with its 3.5-liter twin-turbo V6, albeit with the same increases and decreases akin to the Mazda curve as it reaches 7700 rpm.

Daytona/low drag aerodynamic configurations have also been specified for each car, with options granted for each model. This is one area where further evolutions could take place leading into the Roar.

The PC class has been set with the same BoP as the 2016 race.

In GTLM, the brand-new mid-engine Porsche 911 RSR (above) has been assigned a minimum weight of 1240 kgs (2734 lbs) while the rest of the existing cars vary from 1230 (BMW M6) to 1240 (Corvette C7.R) to 1250 (Ferrari 488) to 1265 (Ford GT).

GTLM also makes use of the same turbo/non-turbo air restrictor and lambda practice employed last year in the class. The two naturally-aspirated cars have restrictors (Corvette with two 29.9 mm and Porsche with two 31.2 mm) and all five models have minimum lambda targets to hit.

Ferrari’s twin-turbo V8 has the leanest fuel supply (1.10), while more fuel is allowed for the BMW (0.96), Ford (0.90), Porsche (0.89), and the Corvette (0.88) which has the friendliest air-fuel ratio.

Of the three GTLM turbos, only Ford’s twin-turbo V6 has received adjustments to its boost curve profile. The changes appear to be made in an effort to smooth the curve due to the granular nature of the changes building to the 7800 rpm redline.

Minimum rear wing angles have been set at the same numbers for the four existing models; Porsche’s mid-engine 911 RSR, with its bigger diffuser and more efficient rear aero, will have its minimum wing angle set after Roar data is gathered.

For fuel capacities, the Ford has been given a two-liter increase to 90L; the new Porsche will start with a baseline of 92L.

Of the nine models listed in the GT Daytona class, few changes have been made for the six existing cars. Among the familiar players, Aston Martin’s V12 Vantage GT3 has been saddled with an extra 50 kgs (110 lbs) to take its minimum to 1300 kgs, and the Lamborghini Huracán GT3 has lost power through smaller air restrictors (down one mm of through flow to two 39 mm openings).

The other changes are reserved for the three new GT3-based GTD models from Acura, Lexus and Mercedes-AMG. All three will start at 1320 kgs. Initial fuel capacities have also been established for the Acura (98 liters), Lexus (94L) and the thirsty Mercedes-AMG (106L).

The entire GTD class has Lamba settings listed across a narrow band – from 0.92 (BMW and Ferrari) to 0.86 (Lexus). The last item of interest involves the Acura’s boost curve. The 3.5-liter twin-turbo V6 will run at the Roar with more bottom and peak boost than the other turbos in the class, but its midrange numbers have been pulled behind BMW’s twin-turbo V8.