Charlie, with the windings I am using, I get approximately 450 volts at C-4. My digital VOM jumps all over the place but if I am not in test mode, a solid 450 volts. I am considering going to a 600 volt .47uf cap. Physical size limitations however prevent me from doing this right now..

Rob, thanks for making the revisions and additions to the PCB and component overlays. It looks foolproof now..Well, for this old fool anyway! Ha!..
Since I made the changes on mine, it has been firing non-stop for 16 hours on my bench supply without a problem at 7000+ rpms. I regulated the voltage down to 5.5 volts for the test..Actually on a battery pack, it will still operate at a voltage of 4.4 volts.. then cuts off... Nice! Lets you know that the battery needs recharging for sure.

Charlie, I wound some toroids to 450 turns and get 450 volts plus..higher and the caps blow..not immediately but eventually..so I would say, between 400 and 450 is about right.

John