Twincharger controling system

[Robert Scott Winnicki]

I am curently trying to build a controler for my twin charged 87 TII RX7.
The car has a 40 CI Supercharger blowing through the stock rx7 turbo.  THe
SC has a electric clutch and is curently manually operated (via a triger
on the shifter)  I have two pressure gagues mounted on the car (one
pre-Turbo and one post turbo)  Right now I usally triger the SC at about
-10 Hg then let off on the SC when I see the pre turbo gauge starts to
drop.  In addition I have a one-way check valve that allows the SC to be
bypassed

The problem:  It is really hard to manually turn on and off the SC during
anything but dragging (straight line stop and start)

I want to make a circut that will compare the pre turbo and post turbo
pressures and operated the SC according.  Any ideas?  I think I will have
to go digital, but I suck at designing circuts.  

thanks
bob