...........let me step up on my soap box here for a minute: With regard to a Banshee style engine, power valves can make sense if electronically controlled in a cylinder designed for them. On the other hand, the mechanical pressure responding valves found in a Cheetah, some Big Block Twisters, T-Rex's, etc., need a very specific set of conditions to work properly. Aftermarket cylinder block designs have progressed to a point with Banshee style engines that power valves don't make sense for most folks.
If y'all are interested, I can dive deeper into this.....