Yea sry I just read that earlier...I should really stop drinking and posting at the same time lol....

 

Swapping to a stiffer spring and shimming a spring will have a different effect on how a valve functions. Here is an excerpt from an email I sent earlier today to a CX7 owner:

We have rough estimations for the springs that are as follows:
Black 8 and less
Green 5-10
Yellow 15-23
Blue 23-30
Red 30 and up
(these are all the springs we make for valves, you will only have 3 of them
I believe)

But that will vary a bit based on the install height of the spring from
valve to valve, the relationship of surface areas mentioned above, and how
much boost AND vacuum that a car will see. The vacuum is very important but
most people over look it.

Shims are used to increase the static pressure required to open the valve.
While the amount of force required to open, for example, a spring with an
un-shimmed static value of 15 psi and one that has been shimmed from, say,
10 to 15 the force to open them will increase at a different rate the
further the springs are compressed with the un-shimmed spring requiring more
force.

As a rule of thumb you want to use the softest spring possible that will
keep the valve closed at both WOT and during boost onset. Real world factors
that prevent us from just throwing in an extremely light spring in all of
our valves are the aforementioned boost/vacuum relationship, pressure
differences from that seen where the valve is mounted and in the manifold
reference to the top of the valve. This will come from both latency, time to
reach equilibrium, and pressure drop due to restrictions in flow such as
irregularities in the charge-piping and inefficient intercooler cores.