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 Seperating out Power Piston Springs 
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Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
Well, after tearing apart 7 q-jets with most of them being spares I have built up an amazingly different group of power piston springs. For my mild build I doubt I will need a super soft one but it would be handy to have an idea of the point where each overcomes a specific vacuum. I was thinking of tapping a spare body power piston cavity for a vacuum nipple and attaching it to my car which currently has 20in/hg at idle. If I used 2 tees, first a tee with a needle valve, then closer to the carb body a second tee to plumb in my vac gauge. Then I could slowly crack the needle valve allowing it to bleed vac until the power piston moves.

Has anyone done anything like this?

Tue Sep 20, 2016 2:14 pm

Joined: Sat Mar 29, 2014 10:27 am
Posts: 42
Try this:

Tue Sep 20, 2016 3:22 pm

Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
Ya, I saw that. I wonder if we should simply be rating springs by the vac they move or if we should also consider the rate at which they over come the vac. Like a mechanical advance spring. It has a rate and not simply a point of start. I wonder if it would be worth figuring the force the vac applies to the power piston are and figure the spring rates or simply track movement. Probably have to use a spring force calculator to get K though, I doubt if I can find that light of spring tester.

Wed Sep 21, 2016 5:14 pm

Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
This is one of the reasons I didn't understand Roe's suggestion to cut a spring (though I did it in my 2gc). Spring force has to do with active coils and coil thickness. When you cut a spring it will actually have a greater rate at the same level of compression because there will be less active coils.

Wed Sep 21, 2016 5:26 pm

Joined: Sat Aug 24, 2013 7:57 pm
Posts: 152
Location: Frostburg, MD
Too bad the z28 fellow didn't test to something like .200" movement.

Wed Sep 21, 2016 9:50 pm
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