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The SC12 supercharger is a positive displacement Roots-type blower. This means that it moves a fixed volume of air per rotation of the supercharger lobes. Boost is generated by moving more air into the engine than it can consume at atmospheric prerssure... boost increases until the engine will swallow the same volume of air that the supercharger is feeding it. Changing the pulley changes the ratio between engine speed and supercharger speed, so the supercharger feeds an increased volume of air for each revolution, thus increasing the boost pressure.
You could actually increase boost pressure by putting restrictor plates into your intake. The boost would increase until the pressure was high enough to force the same volume of air through the restrictors. But this would be counterproductive in increasing power. Conversely, you could port out the head and intake manifold to make the intake less restrictive. Your boost pressure would actually drop, but the engine would have increased flow and increased power.
Without changing pulleys, you can slightly increase boost pressure by trying to improve the volumetric efficiency of the supercharger. First you would want to minimize intake restrictions in front of the supercharger, as any pressure loss in front of the supercharger will drop your boost. You can also port out the intake of the SC12 supercharger to help minimize the pressure losses. Finally, I have also heard of water injection in front of the supercharger to help seal the supercharger rotors and increase the volumetric efficiency of the supercharger.
I don't expect you would gain much from any of the efforts I just listed, while going with a new pulley will provide known significant gains in boost for probably less money.
As for twin charging the 4agze, my twincharger project is still in progress. It is taking a lot longer than I had hoped, and the current economy is somewhat to blame as part suppliers no longer keep items in stock, but rather build to order these days which causes significant delays. My twincharger project is fully custom with all the work being performed by a reputable local shop. And as such, I am taking a very expensive path for this project, but I hope the final results will be worth all the effort and expense.
You can find more details about my twincharger project on my garage page of this site.
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