Ok, that's good way to confirm how far they open.
What about 1st, 2nd or 3rd, did you run it up to your highest RPM?
Looks like reving it up all the way to 6000 rpm in the lower gears is something I will have to try today. It may be silly, but I hate the idea of reving it that high after all the work that has gone into it in the last years (I told you I'm silly ;-)
BTW: I couldn't find a redline value for the '71 351C-4V in my documentation. Would 6000 rpm be safe?
Regards, Manfred
I understand your not wanting to rev it. I was the same way.
But once you feel comfortable that your motor will turn you will find yourself visiting that spot (and the gas station) more and more often....
The bottom end of a 4v motor (4 bolt main) will have no issues with 6000. Your limiting factor is going to be either cam (fall off in power due to grind) or valve spring float.
I usually run it up until it doesn't feel like it is pulling anymore then switch gears.
The different springs control not only when but 'how fast'.
I don't understand your logic in picking a spring. If you started with the heaviest and went lighter until you 'feel' the secondaries open and then went back to the heavier, wouldn't you cause them to not open? I am not trying to flame or nit-pick, I just don't understand.
On my setup I can feel the secondaries 'kick in' as I go past the 2500 or so RPM range, I assumed I would want a lighter spring or one that kicks in earlier.
And I still would like OP to clarify if he has run it up to max RPM in 1st, 2nd or 3rd gear.
Generally you don't want to "feel" the secondaries kick in. You want a seamless increase in power. The method 72HCODE suggests will determine the correct spring for that. The "kick" you feel from the secondaries is actually recovery from a hesitation which may be caused by using the incorrect spring and results in a slower car.
ok, so the lighter spring causes them to open sooner and what you feel is the engine catching up to the extra air flow? I am trying to figure out the mechanics of it.