The ACO has reversed initial plans of allowing teams with IMSA-specific engines to compete in the LMP2 class at the 24 Hours of Le Mans.

ACO Sporting Director Vincent Beaumesnil revealed that only LMP2 cars with the new-for-2017 global spec Gibson engine, as well as grandfathered prototypes, will be allowed to compete at Le Mans next year.

“The American teams, they will have to run a LMP2 car [with a Gibson engine] if they need to come to Le Mans,” Beaumesnil said Thursday following the ACO’s annual press conference.

“I think we have already explained that a few weeks ago. We have some meetings this week and at this moment are exploring other possibilities.

“Right now, it’s the plan for the moment. We’re still finalizing the discussion.”

The FIA and ACO have yet to meet with IMSA executives this week in Le Mans, with both President/COO Scott Atherton and CEO Ed Bennett having been delayed by travel issues.

ALMS founder Don Panoz was the only U.S. sports car racing dignitary in attendance at Thursday’s annual ACO press conference, although IMSA’s Vice President of Competition, Simon Hodgson, and Director of New Racing Platforms, Mark Raffauf, were also on hand.

With talks still ongoing, Beaumesnil said he wouldn’t rule out the possibility of IMSA teams being able to adapt their new DPi machinery to LMP1-L regulations, which receives an overhaul for 2017.

“If you want to race in LMP1 Privateer, you bring a car complying to the rules of LMP1 Privateer,” Beaumesnil said.

“It’s up to the guys building the cars to determine this but I believe it’s possible.

“There are a few things, but it’s nearly the same chassis rules. Globally, there are no major differences. There are a few ones. But I feel it’s possible.”

IMSA, the FIA and ACO first announced intentions last year of IMSA’s DPi concept, minus the manufacturer-specific bodywork, would be eligible to compete in the LMP2 class at Le Mans.

The three parties have since backtracked from those plans, largely in a dispute over electronics, with IMSA opting not to adopt the FIA and ACO-spec Cosworth ECU systems due to manufacturer’s wishes.

It’s understood Mazda had been seriously evaluating a Le Mans effort around its soon-to-be-announced DPi program.