It appears to have a #5 power valve. According to mu in gear warmed up vacuum (12.5-13) I should be running a 6.5. A buddy of mine suggested going to a 4.5. Your thoughts on this?
No need to lower it, that's for sure. As far as the race track, you'll have little to no vacuum at wide open throttle, so you'll be good there regardless.
PV tuning is all about part throttle acceleration/performance. The farther apart you're cruise vacuum is away from the PV opening rate, the more throttle opening you'll need for enrichment. Every combination will be somewhat different, but if you feel any lag or the need for excessive throttle when partially accelerating from cruise speed, raising the number will generally help with that.
Most subscribe to the "half" method, and that's certainly a reasonable place to at least start. My personal preference on engines producing middle of the road vacuum has always been to be a little closer then 1/2. As a example.....11" idle/14" cruise, I'd generally run a 8.5" PV.
