IMSA is set to take a further step towards the finalization of the DPi regulations with the imminent release of its constructors manual to manufacturers.

Sportscar365 has learned that the manual, which details the engine, bodywork and other associated regulations to transform a base LMP2 car to DPi specification, will be released next week.

“It’s the evolution of the philosophy documents that have been issued since August of last year, to the OEs and the four constructors, once they were chosen,” IMSA’s Director of Racing Platforms Mark Raffauf told Sportscar365.

“On our side, we’re pretty comfortable, both with what the constructors and the OEs need to know to build one of our cars; they know what the process is on how we’ll verify their car; they know the process on how we will balance that to the standard [LMP2] car.

“All of those processes are in place and ready to go.”

Despite previous reports of IMSA potentially moving further away from the FIA and ACO’s global LMP2 platform, Raffauf said there will be no changes to the the ACO-homologated suspension, gearbox, floor, splitter, diffuser, wing, cockpit or shark fin.

“The basic principle is that you take the core of the LMP2 car, you skin it and engine it,” he said. “There are certain deviations in the bodywork that’s allowed.

“There are certain deviations that will be needed to have different engine installations fitted to the same kind of chassis, and they have to be tuned with each OE as we go, because they’re not the same.”

Raffauf said that engine manufacturers must run the same gearbox that will be homologated to each LMP2 chassis, although the gearbox will be the choice of each constructor.

DPi cars, meanwhile, will be permitted to make changes to ancillary components, such as exhaust routing and cooling for turbocharged engines, as well as possible changes in electronics.

However, in order for the cars to be compliant at the 24 Hours of Le Mans, Raffauf said they will need to be operating in the final ACO-homologated configuration electronically, as well as with the standard LMP2 bodywork.

“In principle, that car combination/engine has to run to their rules to Le Mans,” Raffauf said. “We’ll obviously help [assist the ACO] with engine information.”

IMSA has also detailed a schedule for the DPi evaluation and homologation process, which will begin ramping up activity shortly.

Raffauf said the process will begin with virtual model testing, followed by physical, 40 percent scale model wind tunnel tests by mid-May and full-scale testing by late summer.

Three wind tunnel validation tests at Windshear have been scheduled for September, November and December, with IMSA-sanctioned on-track tests at Daytona set for November and December.

All new DPi and LMP2 cars will be exempt from IMSA’s testing restrictions, with Raffauf expecting the first on-track tests to begin in August, prior to the final homologations.

“The object is to get them out there, test them, figure out what you need to work on and not to work on, in that sense,” he said.

“Even if they have a pretty good design in theory in design in the tunnel, with the scale model, and it doesn’t pan out, they aren’t stuck with that. They have five more months to tune that.”

In terms of DPi interest, Raffauf said four manufacturers have been working diligently with them since last fall, with a few others potentially waiting in the wings should their programs get the go-ahead.

“It just seems to be getting better,” he said. “Whether they all hit their marks for Jan. 1 or not, that’s not easy to say.

“Whether they all get their final approvals is not easy to say. I can say we’ve had pretty steady dialogue with a solid four [manufacturers].”