Those are 502 MAG EFI that Lingenfelter modified to 525-540 HP. He developed the EFI system for Merc so he knew the limitations. Extrude honed intake, head work, cam, Eickert headers, bigger injectors, more fuel psi. These motors are @ max in NA form. It is all top quality parts. However he is deceased and I don't know if his shop is still in business in Decatur IN, home of Formula.