Actually, It looks to be the "Grand Thumper of them all" a BSA Gold Star (500cc). And that's not the newer version made in the 60's. I'm talking mid 50's or so. I mean, you take a mildly built Gold Star, trim it down some and replace the muffler with a reverse cone megaphone and you've got a motorcycle that runs and sounds Strong. The only thing is when a Gold Star is for sale, you've got to have big bucks to get it.