Weber Powervalve Questions

[atd350]

I dont want to reinvent the wheel here, but as I have a progression plan for the current engine, I was wondering if anyone has ever played with the powervalve in 32/36 weber carbs?

Firstly, I am led to believe the standard powervalve opens at around 18" of vacuum. That sounds like a lot, basically meaning its open 90% of the time. if it was 10" or 12", that would make more sense to me. I imagine for a lot of big cam engines, it would be open all the time, including idle, as they would never have more than a few inches of vacuum.

Has anyone ever modified one to open at a lower vac point by cutting the spring down? I believe this is relatively common with the Jeep guys.

Secondly, I plan of using this carb for blow through and i reckon i can modify the PV to open only under boost or on the change from vacuum to boost, by placing just enough 'tension' (as opposed to pressure) on the diaphram, that even the most minor vacuum holds it closed, and boost pressure opens it.

Thoughts anyone?

Maybe I am overcomplicating this.....