there's a shocking lack of information out there about the coyote valvetrain and its requirements to work in a road course environment. To the point where people either are willing to guess and try random parts (usually at their own peril with mixed results), or stick with the factory or factory "racing" parts (usually at their own peril with mixed results) Doing my own research, I believe the PAC-1234x spring may have been used by Roush Yates Engines to build out their IMSA/PWC 302R upgrade engines. That information is unconfirmed but I've reached out. What I wanted to find out is have people successfully used aftermarket springs/retainers/valvetrain components for a length of time with excellent reliability? I can count a dozen broken motors on here that had aftermarket parts there, (though as many if not more stock ones as well). The concerns with the PAC spring I've seen are: Its 240lbs/in, Seat Pressure 92 @ 1.575" (100 @1.500) Open Pressure 200 @ 1.000" (though I've seen 218, 230 as well for different specs) (though numbers vary depending on install height, cam lift and other factors) The boss 302 oem spring (which can vary significantly) 67lbs (300N) to 157lbs (700N) its a bit of a jump and presents the following concerns: Will it bend or break the hollow valvestems of the boss 302 valves? (PAC says no, internet says maybe, 1 case of a turbo car doing such) Will VCT work with it? (some say yes, some say yes with less accuracy, my tuner says absolutely not) Are they a true drop in? (pac says yes, but recommends Ti retainers) I'm looking down this rabbit hole as one of my failures may have been related to a boss 302 valvespring failure (or float near redline). Obviously I can lower the redline and try to avoid the limiter, but sometimes in racing all bets are off and I want to engineer the strongest most reliable setup I can.