[Steve C.]

Stated above- "...but I want to target a spring seat pressure of 125-130 AFTER break-in."

Good point and brings up an important topic and one often overlooked The fact that springs can and often do lose some pressure after run in and use.

Here is one example documented in a build done by the noted Ken Crocie. In use was a Comp hydraulic flat tappet cam. The valve spring pressure was set at an initial setting of 130 pounds on the seat, with 320 pounds open pressure.
After running on the dyno, he knew the valve spring pressure would ease down toward Comp Cams rated value of 117 pounds on the seat. The actual pressure after a day on the dyno was 122 pounds.

Another nice example from mgarblik who posted a few years ago with a build using dual springs with 135-140 on the seat. However on this particular build the cam was broken in on the dyno with the inner spring removed.
His posted comment..."BTW, also consider if the springs are new, after running the engine for an hour, the outer springs will lose 8-9 Lbs of seat pressure as well. (10%) is typical so when the inner is reinstalled in my case, the seat pressure will be 127-132 broken-in."

And related, always check new springs at their intended installed height with their actual intended retainers on a calibrated spring tester. Never trust catalog specs ! I've had new springs that did not come anywhere close to their catalog rated specifications. And from a valve spring catalog.... "Note: spring tensions often vary measurably within the same production runs; therefore it is recommended that EACH SPRING be tested on an accurate spring tester and the springs installed at the recommended SEAT PRESSURE."

And someone posted that the retainers being used can be a key player in this deal as the inner can vary some from one part number to another. This affects or changes spring checking pressure(s) and coil bind as well.

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