The "cut-in" points are approximate as there are variables in that equation.
The "orange" spring is a copy of the spring used in many factory "high performance" carburetors, 350/350hp, LS5, etc.
The light blue is close in cut-in point but lighter spring wire with more coils so the rate is a little quicker.
Those are the two that I use the most here. For early applications that used manifold vacuum to the advance, and small cams with high compression the green springs works well.
For trucks and HD applications with small cams and used for towing, or anytime you want the PP in very quickly used the dark blue (plain color in some kits) as it has the highest/quickest rating.
The apprx cut-in point are 5-6" for the orange, 6-7" for the light blue, 7-8" for the green spring and 9-10" for the dark blue spring.
I recommend the stronger springs for stock and very mild applications. I use the light blue spring a lot here as many folks have put pretty "hefty" cams in these engines which don't make a lot of vacuum at idle speed.
The orange spring is an excellent general use "high performance" part that works well in a wide variety of applications and probably why the factory used it so much in their HP engines......Cliff
