Pretty easy math. If you spin and engine 8000rpm and ruin a 3 vane moroso it will need to be underdriven 20%. If you run say an enhanced 4 vane it can be driven 1 to 1 at 8K. Spinning the pump as close to max rpm as possible will yield the highest vacuum possible as its linear, it wont make 20+ at idle that generally requires a fair amount of RPM not to mention a very well sealed engine.