The customer originally had a more or less decorative little B&M 144 peanut blower, which was completely worn out. Professor Gaynor at SuperCharger Supply offered to adapt the input snout from the B&M blower onto a 3-71, which they built for us. I then machined an adapter plate to be able to bolt the 3-71 to the original B&M intake manifold. The thing made about 10 PSI of boost, so we slowed it down with a larger pulley on the blower to get the boost back around 6 PSI. As for your question, I don't believe a 3-71 builds boost any faster or slower than a 6-71 (assuming you change the drive ratio to compensate for the change in volume). And efficiency... well, it's a Roots blower trying to cram "snap crackle pop" through an unremarkable pair of cast iron Vortec heads, so you end up hitting a wall pretty quickly.
