Quote:

Hypothetical question:

X motor,
with proper X valvespring,
with, say .080 wall pushrods,
With ti retainers.


Then:
change pushrods in above motor to .140 wall pushrods, steel retainers. Nothing else.



Does the motor use the same spring with the two changes? Do the pro builders weigh components or do they simply guess?



If anything, the steel retainer is most likely to change your spring requirement if it does at all.

Not sure what you mean by a pro builder, but if your entire valvetrain system as it is hasn't been tested on a Spintron, it's really a guess. Bouncing the valves on the seats is probably the biggest parts breaker, but there are places between opening and closing that will cause trouble as well.