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Roger Penske says his only concern about returning to the top level of US sportscar racing is how his squad's car might fare under IMSA's Balance of Performance rules.

Penske will decide this summer if it will join IMSA's prototype class in 2018.

It would likely field a two-car, manufacturer-backed DPi or LMP2 entry with star-name drivers including Juan Pablo Montoya and possibly Helio Castroneves, but its team patron sounded a word of warning from his previous experience in the Daytona Prototype category.

In 2009, after concluding a highly successful American Le Mans Series campaign with LMP2 Porsche RS Spyders, Penske entered Grand-Am with a Porsche-powered Riley MkXX.

After finishing sixth in the Daytona 24 Hours, its 3.9-litre flat six engine was pegged back.

"It's great, it's a good series," said Penske of IMSA. "The big issue we continue to look at there is this Balance of Performance.

"How do you get this? We get multiple chassis, and you've got racing engines and production[-based] V8s. One has got torque, one has got high rpm.

"We were in that business for a while and were disappointed because we ran strong at Daytona, and they took sixth gear away from us.

"It took 400-500rpm and they put weight on the car.

"We had only run one race - that was a bit of a tough pill to swallow."