Originally Posted by ErrinV
Mine has the FCR 39. It was on the bike when I got it though so I don't know what the difference is. I understand it's the way to go, but I've never ridden another 640 so I wouldn't be able to you what kind of difference it makes. This bike does haul ass though! Here's the link
for the original ad that may be of some help.
I didn't know you bought Vincent's 640. That's a nice bike. That bike also had the power now insert in the intake. He said it made a big difference.