Complex sentence: Ultimately, Dallenbach's blower was deemed legal, but USAC declared the team could not swap it out for the more fuel-conservative smaller turbo on race day.
Split into simpler sentences: Ultimately, Dallenbach's blower was deemed legal, but USAC ruled that the team had to use the same turbo in the race. They would not be allowed to swap it out for the more fuel-conservative smaller turbo on race day.