Clanton,

only 4 psi? Is that right?

I think it's more than that (but correct me if I'm wrong) because if you remember the 71 series Rootes was designed for a Detroit Diesel....which are 2 strokes. And the supercharger was required just to get enough air into them, I only know this because I worked on and learned a ton from working with big Deisel mechanics as a 'young-un'.

So when you put the blower on a 4 stroke of the same discplacement, each revolution of the blower is packing only 1/2 the cylinders/displacement PER REVOLUTION... so the boost is actually proportionally higher. I think that's how the early Hot-rodders figured out how they could make them work

They used 6-71's on 426 Hemis for decades at close to +/- 1:1 ratios and we know it will definately make more than 4 psi of boost. There are pretty generous efficiency losses between the seals and the case, not to mention air density losses from heat but still the displacement calucation was based on the GMC/ALLISON/Detroit Diesel standard 71 cube cylinders. I thing there was a 53 inch Cylinder as well, a lot of early smallblosks ran 4-53 blowers

i would think an 8-71 on a 440 could be significantly under-driven on the street and easily make big boost.