The owners manual for my Raptor has 'YFM660R(C)' as the model number. I'm curious if anyone knows what the (C) stands for, if anything.

My dealer (Mission Yamaha - Laguna Nigel, CA) told me it stands for California, meaning you have a California model. My owners manual has the same model number.

YOUR OWNERS MANUAL HAS A (C) THAT DOESN'T MEAN YOU HAVE ONE THAT BOOK COVERS BOTH MODELS THERE ALL THAT WAY. EVERY BIKE AND QAUD IS THAT WAY. SAVES THE COMPANY TO ONLY PRINT ONE BOOK.

Actually this is just the version of Raptor that was being tested when they decided to go ahead and write the manual, I think the version of quad I actually got was a YFM660R(N). Meaning it was later on down the line in revisions than when the book was written.

What is the difference between the california version and the 49 state version?

It is something in the ignition box I have heard.

The other 49 state models are just more powerfull and faster.

The cali model is more resticted so it has 32-33hp where as the 49state has 38hp all you have to do is put an exhaust on it and then the hp specs are = so it has to be something in the exhaust look at ctracing.com post both cali raptor and 49 state raptor have close to 50hp (rumored) on either one so this has to mean that the cali exhaust has to be more restrictive it has nothing to do with the ignition.

Actually, they probably both are true. I would figure that also the piped quad would make more power at higher RPMs but it is still limited by the 9000rpm limit in the ignition system. Which is shown by the CT pipe adding 32Hp AT 9000RPM But seriously its probably something in the exhaust, but I would assume at the silencer end.

Also remeber that the yz250f will rev to 13500RPM, so the 660 will probably hold up to that limit or more. The Real limit to the RPM will be the weight of the Piston, Rod, and Crank assembly which is already super light. So with ignition modifications and better breathing these engines can become real screamers on top.