Unfortunately, we don't know what modifications have been done. We're assuming there have been a lot.
The Honda S2000 made some real waves when it first debuted in 1999. It didn't set any new records for overall power, but the amount of horsepower per liter from a naturally aspirated engine was unheard of in its price range. This also combined with a low curb weight to make for a surprisingly quick little car. But the S2000 in the following video could easily be the fastest one you've ever seen, as it's up against a Camaro in a race where they both run 8's.
There was $15,000 on the line for this race, which is almost as impressive as the race itself and certainly makes for an enticing minute and forty-two seconds of video.