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[h=2]IMSA: Roar Before the 24 BoP issued[/h] Monday, 02 January 2017


Marshall Pruett / Images by LAT

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 (0.8 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.