I have an 85 and an 86 CR500. My 85 was in "good" tune the last time I rode it and is the fastest dirtbike I've ever ridden. I'm mostly a racer at heart did alot of motocross at the local and pro level and have had many bikes over the years. My 85 was rated at 63hp stock and right now I'm in the middle of having it totally rebuilt top and bottom with major mods.....Porting, head work, intake port timing, RAD valve etc.... It should be the low 70s range when it's done. Going from my 05 CRF450 and jumping right onto the 500 was like night and day. The 500 is very abrupt and pulls right from the bottom then explodes to moon with enough power to satisfy anyones power needs. It takes a certain finesse to make this kind of power work on the track, and I've found that out the hard way. When I try and ride it anywhere close to the way I ride a 250 smoker I will end up blowing the corners. You need more precise throttle control or the tiniest bump that usually does close to nothing to your throttle hand could make you blip the gas when you aren't ready. VERY SCARY!!!
I found out that if you ride a gear taller and use the bottom end torque to push you around it is much more useable, but it's not as much fun to ride like that. It's hard to use an entire gear pull of full throttle without either running out of ground or doing an unexpected wheely. Now if you have room to play, like a long fire road or some dunes, this bike is GREAT! It will eat anything that comes at you. I've drag raced a bunch of contenders from a KTM525, to CRF450s and they don't even come close. They'll be tapped out and I pull up the front wheel and shift into 5th while I pull away from them. Now I do have some taller gearing than them but I still get outta the hole first. Oh and this was all done on sandy fire roads in the pineys.
All that being said and having the 450 to compare it to, IMHO the 500 makes like 10 more HP, I can feel it, and if you can feel a difference like that it's a big deal. The CR500s are in alot lower state of tune than any of the 450 mxers out there today. There's not much more you can do to make the 4 bangers THAT much faster and still have reliability, they are in a higher state of tune right out of the box. The reason I'm rebuilding my 85 is because it still had the original piston in it and I'm currently in a vintage racing organization that I need the bike for the Vintage 80s class. First race I did with this bike I got the holeshot.
The numbers are out there somewhere, you just have to look for them. I did. I spent so much time researching the 500 and have seen so many sites with info on them it's crazy. Here is a short video of me hitting a sandy berm. On the track I can go almost as fast on my 85 compared to my 05 450, it's the suspension that makes the difference, on these sandy, whooped out tracks it's all 500 baby!!
CLICK HERE FOR THE VIDEO