It was quite loud - in the american V-8 type range rather than a high-revving italian type range. I only saw it for a few laps, but it didn't seem like it was pushing too hard.
There were other odds and ends on the track as well.
The Can-Am type car was the loudest of the bunch.
There were also two bandelero type cars that looked very fast and did a lot of laps, but I didn't get photos.