Yep, they left it unrestricted, but I had fun last night with a RM Cappuccino taking on the RX-7s and similar cars in the FR races. Much slower on straights, but defiantly faster through the turns.
The wording of the events make it seem as though higher horse power cars wouldn't be locked out- Think of it as a guideline. I don't think it was a mistake.
if you just stay under the average of the a.i. you have an challenge did the FF with an toyota vitz with 187 bhp (non turbo) challanging enough on the eiger