First of all, I wanted to start this thread out by saying that ATI Procharger has went well above and beyond the call of duty to satisfy me as a customer, and has exceeded my expectations by their customer service. In short, I say this because I have owned A D1SC head unit for approximately 9 years. I've had on going sealing issues with this unit, and as of recent sent the head unit back to ATI for repair. Long story short, ATI warrantied the supercharger even though it was 9 years old, and they replaced the unit with my choice of a D1SC or D1 oil-fed. Again, this was well above my expectations and I want to publicly state my appreciation for their support. With that said, I've decided to go with the D1 oil-fed unit over another D1SC simply because it has a higher step up ratio of 4.44:1 over the D1SC 4.10:1, and has a higher max rpm speed; 62000 vs 65000. Therefore, I'm wondering how the boost curve will look compared to the D1SC, and if there will be any power gained by the higher step up ratio? On the D1SC I was running 3.1" pulley, however ATI swapped a 3.4" pulley in the new D1. This bring the impeller speed down to around 56165rpm, from the 56400rpm the D1SC was spinning to. According to ATI, I will still make more boost.