"The Cure" External Power Valve Control
I have developed this system to control the p.v. in blow thru applications. It works similar to the Crutch, but does not use a motor. The valves can be sourced on ebay, used and new. There are other models that can be used, research their limitations and specifications carefully.
There may be instances where the Crutch would be preferred, and instances where the Cure would be prefered. If properly thought out, the Cure could be used to control vacuum advance diaphragms to keep timing high to help spool as well, with another unit. I have not used one to control timing yet. Use at your own risk. 100% reliability so far using to control p.v.'s. Over 2 years on one combo(24psi), and since the beginning of my build(20psi). Here is an installed pic, it's on the firewall between the hat and heater hoses:



