Thanks Sibster, the modified valve turned up , so i can see what you mean.
should i use the spring to return the valve to 'closed' rather than gravity?
i have yet to try it on the car
but without it i was only getting -5psi instead of -11, with my piss-poor homemade valve
not getting any bangs or pops, hopefully using your valve i will get some proper results
Back to the original reason for the post, my ignition is now happening at 7 degrees ATDC, does that sound about right?