Increase compression wich increases torque and HP for far better acceleration and top speed. Best bolt on product for any watercraft is increasing Compresion. Stock 550s run around 120 psi cranking presure stock this head brought mine up to around 180 wich is safe for super unleaded (yours maybe different due to what bore size your on or if cylinders have been ported or what shape you're top end is In and how well rings are sealed up! ) I have ran as high as 190+ psi on super unleaded with no problems just need to richen up fuel with carb screws