>SD = Speed Density. Thanks, cleared things right up for moi :) Frederic Breitwieser Homebrew Automotive Bridgeport, CT 06606 Portable Web-Site: http://www.geocities.com/MotorCity/Downs/4605/index.html Vehicles: 1989 AG Hummer 4-Door 1993 Supercharged Lincoln Continental 2000 Mid-Engine Sports Car <smile> ---