difference between OS pre-surpass and..
 

Hello all.... whats the difference between the older design OS pre-surpass engines and
the more modern surpass engines? I have an older pre-surpass 120 4 stroke that I aquired and had it totally rebuilt- new bearings, ring etc... and was wondering whats the power difference from the newer engines of today? I plan on putting the pre surpass 120 on a GSP
hellcat and was just wondering on the performance I might expect?
Thanks in advance!!! John

RE: difference between OS pre-surpass and..
 

when os first made the four strokes (pre-surpass) they were weak engines. also, they had no corrosion protection and their pumped versions didn't work very well. the name surpass comes from the fact that they surpassed their previous four strokes in power, reliability and long life. your engine will probably work fine. jsut keep in mind it will most likely have less power tyhan your buddy's 120s.

RE: difference between OS pre-surpass and..
 

The main difference is that the Surpass series have a larger diameter intake valve which improves the volumetric efficiency. Expect to see 600 t0 800 rpms less with the pre-Surpass on 16 and 15 inch props respectively. A perry oscillating pump will improve reliability.

RE: difference between OS pre-surpass and..
 

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