Fixed Open Powervalve question

[Hillclimb#42]

First, I want to say that my 500's powervalve is operational. This season, I studied what was posted on here and the other fast riders that rode kx500's. I tried to use anything and everything from both, that made sense to me, to apply to my bike. Most everyone hillclimbing runs the FMF Gnarly, I think, with the FMF Powercore Silencer. My engine builder who is also involved heavily in Pro Hillclimbing suggested that I weld the Powervalve open like they do on Pro Bikes.

  I am running the Pro Circuit II with the FMF Silencer. My bike sounds like it should in my mind. Like a set of new glass packs on a tuned V8, in my world anyway. The thing is, the other guys that race them on the Amatuer Level have their 500's sounding like a 250. Very clean, very "ying, ying". I know that they spend lots of money to get them tuned and maxed out, but I was wondering what freed up their motors the most.

Anyone ran their powervalves stuck open for drag racing or hillclimbing that can comment on the difference in sound and performance? I understand that I will lose bottom end and noone really recommends it for typical riding. How about the FMF pipe? Does it just sound different? Is it just the difference between stock porting and super modified porting?
How about anyone that has had an out of balance crank that got it straightened out? What did that do to the sound or  what affect did that have on performance?

I guess thats alot of questions for one thread, but I searched, and the last post was very old without the answers I needed. Thanks

[stewart]

i would not disable the power valves

[KX500freak]

when i got my tracksumo in bits n pieces ,
found the mainvalve was removed by the previous rider.
i took it for one trackday with this exsisting setup.
the bike had more top-end speed but in combination with a very lean fast jetting ,
a piston had to be changed like 6 times per saison 
so i installed the mainvalve back in,
and got me a 180 main instead the 170 sitting in it back then.
it,s better with all valves ,much more bottom power,a little less top-end 
 

[don46]

Kyle,

We have ran the power valve on our nitrous bike locked open, thats the bike we had in Nashville last year. The 500 in the 05 is hooked up and works well.

Have you done the window mod, or the head mod? those make a huge difference. I wouldn't go with the FMF pipe, just because everybody else does it doesn't make it right.

Those bikes that sound like 250's are they kawis? actually I think my 500 with the head and window is really responsive.

you can get rid of some rotating mass to make it quicker revving, thats not necessarily the best soloution for what you want to do.

[Hillclimb#42]

 I wasn't really wanting to lock them open, just wondering if that made it sound like that. I thought that mod was mainly bored and sleeved cylinders to do the 540 deal. I guess Nitrous would give you back the bottom end, Don. That's, Crazy... Nitrous on a 500... The bikes I have seen that I'm comparing to are Kx's, but in the 600 Class, just trying to get at what they probably have done. I like the Pro Circuit II pipe. No doubts on that, especially with both Stewart's and Don's advice. I have a windowed Wiseco, but it is as they shipped it to me. I'm not sure what I have, if anything in the head. Watson and Thomas used the best of two motors to get mine together. It did have an adjustable powervalve bolt-mod that was very handily already locked to the right measurement. V-force reeds and the pipe is all I know for sure that is not stock. 
  My 500 is responsive. Don't get me wrong. Its super fast rev, but maybe not 100% on max RPM. It also sounds more powerful and aggressive, than some others, I guess, but I don't want to overlook things done by guys often running Fast Time of the Day and King of the Hill runs. Nor would I discount a guy's advice with 3 Land Speed Records or one with a 2009 Pro Hillclimb Championship. Congratulations, by the way. I am thinking of putting stretchers on the beast and running the 600 Class next year. Beating the Stock Length 450's will never get old. But the faster I get, the more dangerous Stock length is getting.