For your application, I believe an 8-71 will be a waste. It's all about using a blower to its full potential, especially with a roots blower. The more power that comes from the blower itself, the more efficient the engine will be, as long of course other things are taken into consideration such as the addition of an intercooler. Keeping air temps down, a 6-71 should be enough to boost all but the most serious big block combination.....if done correctly.