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I spent the day making up brake lines to fit the 3 configurations, bleeding each one and testing while trying to record it all on video. As @JMortensen suggested, compressed air is NOT a good substitute for brake fluid when testing a prop valves as you will see. So to any future readers please ignore my conclusions in the first post. The Wilwood prop valve acted exactly as you would assume it would with each turn cutting off a bit more pressure until the minimum was reached. This testing was done on a 72/240z with a new 15/16" Master Cylinder, rebuilt 280z brake booster, all new Cunifer brake lines, SS flex hoses and Wilwood 120-6816 4 piston calipers on the rear. The fronts brakes were not tested. - the first configuration was 15/16" MC straight through to the calipers with NO prop valve and I assume no vacuum booster assist as the engine was not running. 1200 psi pushing as hard as I could. - the second configuration was with the stock 240z prop valve installed, 600 psi pushing as hard as I could. - the third was with the Wilwood 260-12627 prop valve installed and the stock prop valve removed, you’ll notice that with the Wilwood prop valve installed with the valve wide open there is a 100 psi decrease in the total pressure down to 1100 psi from 1200 in the 1st video. wide open, 1100psi 1 turn closed, 1050psi 2 turns 950psi 3 turns 950psi 4 turns 875psi 5 turns 750psi 6 turns 750psi 7 turns 650psi 8 turns 600psi 9 turns 600psi 10 turns 575psi 10.5 turns 575psi I took it out for a run with the prop valve turned all the way closed to 575psi and I that’s just about right. I warmed up the brakes a bit then tried a panic stop, PS rear lock up but none of the others. Tried the same thing again and the DS front locked up but none of the others so I’m pretty close but will continue to test and play with it. So the front brakes are now getting 1200psi and rear 575psi. https://youtu.be/FWQ2V-w1Av4 For some reason the 3rd vid won't embed but the link is above.