That's a very good question. We messed with different settings. One tilted forward, one level, and believe it or not, it didn't make much if any difference. I like to have mine level when engine is in your car, mainly just for setting bowl levels. Alot of engines are tilted back to align the driveshaft to the rearend. On that application I would probably use the tilted intake, other than that I would run the intake that is level....