Hello John, The valve is just one of many differance's that make the surpass models different. case designs that allow better cooling, some have larger bearings than there non-surpass counter parts. The Intake valve's larger, but so is the port, & the intake track (path the air-fuel take) has been improved for better low & high speed air flow. Larger carburater's, & pumps on some to allow more consistant fuel delivery from full to empty tank. Some improvments in the exhaust also allow better flow. The camshafts are different. Allowing a wider duration of total valve timing, a higher lift, & a longer full open duration (wider nose of the lobe). Some also have a different rocker arm ratio, allowing a slightly higher valve opening from any given cam lobe height. All that to say the surpass serie's were developed to improve on the 4-stk power output that some earlier engine's just didnt have. Not to say the old ones are no good, just not as powerful as the newer one's are. I have an old 120 with the separate valve covers. still runs good. My surpass's have a little more power, but the plane the old one's in is not a high speed type. The power is right for the plane it's in. Hope this help's & good luck with it. proped right, it will serve you just fine. ..............Mildbill