I know for sure Eric built a 500 engine for one of the local racers that he works with and it has been holding up really well, I believe Eric has a few of them out there at this point. He has been having internet connection issues lately but I'll see him tommorow and get an update.
Rich: just so i can arm mself with more useless trivia to bore people with, what size piston is being used for the CRF bigbore and is it really a 500 or just a 480 that i have seen advertised?
Bruce - Eric has done a bunch of 99mm(478cc) with great results. It's just an overbore and replate of the cylinder. The OEM Honda barrel looks to be plenty stable even with a 3mm overbore.
The 101 mm setup (498cc) requires sending the barrel to Wiseco where they weld in an aluminum sleeve from Advanced Sleeve and then bore it to size. Initially there were problems with this process but that appears to be cleared up at this point. Eric has one of his riders with a ton of hours on his 498 and it's only needed piston replacements. The dirt trackers like this setup and they push the engines really hard so it's hard to know where the failures that do occur are coming from. The OEM Honda rod seems a bit dodgey when these big bores are run really hard. Not unlike the YZF big bores. Crank maintenance can't be fudged with this setup.
The 99mm setup with a trick stroked crank (about $1600 for the crank from Falicon) seems to be the hot setup for the dirt track guys running CRFs. That along with $1800 worth of head work from Woody Kyle or Ron Hamp. LOL :)
I have a 99mm barrel on the way and a spare cylinder head, so I'm going to take a look at how well they work together on the flow bench.