There needs to be an even greater cost reduction in the new FIA World Endurance Championship prototype rules announced if they are to be adopted by the IMSA WeatherTech SportsCar Championship.
The target of the WEC rule makers has been to reduce budgets in the premier class to 25 percent of current LMP1 levels on the introduction of the new category for the 2020/21 season, but IMSA boss Scott Atherton claimed that this is not enough.
He maintained that the rules as they have been outlined so far would result in budgets significantly higher than in IMSA's existing top class made up of DPi and LMP2 machinery.
"In many areas we are completely aligned, but I would say the one category that continues to be a point of separation is budget," Atherton told Motorsport.com.
"Even with the significant reductions announced it still represents a big increase from where we are with the DPi and LMP2 formula that is working well."
Atherton insisted that it was still IMSA's desire to have a common prototype class across the WEC and the North American series by 2022.
"Our mission right now is to do everything we can to have common regulations," he explained.
"We will be working aggressively in that direction over the next four or five months before the rules need to be ratified at the end of the year."
Atherton revealed that IMSA wasn't against the energy-retrieval systems that will be part of the new WEC rules but are not part of the DPi/LMP2 formula in North America.
"Hybrid is not a sticking point — we are happy to embrace that," he said. "What becomes the challenge is how you control that technology and the cost."
Atherton said there was no plan to bring forward the introduction of a new top class in the IMSA to closer align the series with WEC's regulatory time line.
IMSA extended its current prototype rules to the end of 2021 at the beginning of this year, which means that it would be nearly 18 months behind the WEC should it adopt its rules.
The 2020 WEC rules announced yesterday call for pure-bred prototypes with the look of hypercars or super sportscars.
Only one hybrid system will be allowed, but performance levels will be similar to LMP1 levels with a 200bhp increase in power from the new cars' internal combustion engines.