Before I start, yes, I know that turbos are better, especially for high-end performance. I'm more interested in making sure the engine is boosted - and stays boosted - in the low-end, basically from 1k-2500 rpm. The gears on the CX/VX tranny are pretty tall so it would be very easy to stay in that range while motoring around town or what have you. I understand that Jackson Racing used to make scs for D-series engines. Is that the best sc to get for a D15Z1, or can an Eaton 3-lobe or 4-lobe be adapted? Some of the efficiency curves I've seen for the 4-lobe TVS are pretty amazing for a sc, though at the same time, I have to think that a TVS would be pretty expensive (and the 3-lobers aren't bad at all, really . . . not at the 50% efficiency range where scs are often considered to sit). I'd also be pretty open to a Lysholm Screw-style sc, but those are pretty rare and are, apparently, insanely expensive. And, in the end, I only really want around 5-6 psi of boost anyway. Of course, CFM is more important than that number, so take my expectations for what they're worth. Alternatively, if there was a way to get a turbo to make around 4 psi of boost at 1500 rpm on a D15Z1, then I could probably ignore scs altogether and go that route.