351LX
Founding Member
The vacuum in your motor is going to drop from say 12" to 1 or 2" when you open the throttle blades.Since the power valve opens when the vacuum is less than what it is rated,your motor sees 8.5" before it will see 3.5" when the vacuum drops off so the 8.5" power valve opens sooner.Think of it this way, you have two coil springs with the same amount of weight on them so both are fully compressed.You start removing weights until one starts to rise.The one that rises first is the stronger one, not the lighter one.Vacuum doesn't open the power valve, the spring opens the power valve.Vacuum is trying to compress the spring just like the weights do.So a stronger spring means it will rise earlier as the amout of vacuum is reduced.