I didn't know he made it into the 6's on his Stage V Hemi. Last time I saw him with that motor he was running 7.80's on alcohol on 34.5x17-16 Hoosiers at 3500lbs. I believe he had already switched to the BAE Hemi by the time he ran 6's.

Roots blower are a constant displacement blower, unlike screw blowers. They become less efficient the larger the motor to blower size. They still work but they build more heat do to scavenging.