ya not mention the fact that air probably cant flow too well with the supercharger screws and intercooler blocking the way. plus the stock tune is very rich even with the boost so the car would have to be re-tuned to really see any kind of numbers without the blower. I've always wondered the same thing though! Would be kind of cool to see someone who converts to a centrifigal supercharger to dyno it without the s/c first!
General rule of thumbs is that an engine with 14.7 PSI of boost (1 Bar) will make approximately double what it would N/A. So, at 14.7 PSIof EFFICIENT boost (meaning non-Eaton boost), these engines would probably make around 550 RWHP. Let's just round and say 650 FWHP. That would put it right at 325 FWHP N/A.