HARRISONMIRAGE

I AM JUST DOING A WINTER REBUILD ON MY 454 CHEV AND I AM LOOKING FOR SOME ADVICE ON OTHER MEMBERS EXPERIANCE WITH SIMMILAR CAMS.I CURRENTLY HAVE THE STOCK MERC.CENTERISE MANIFOLDS WITH CORSA DIVERTERS.I AM PROBABLY GOING TO USE AN IMPCO POWERFLOW MANIFOLD WITH THE SILENT CHOICE RISERS TO HOOK UP WITH MY CORSA SETUP.THE CAM I AM USING HAS A 268/280 DURATION AT .006 & 224/230 DURATION AT .050.THE LSA IS 110*AND WILL BE INSTALLED AT 106*ICL.THE CAM MANUFACTURER GIVES THE TIMING SPECS AT .OO6(INT OPEN 28*BTDC & EX CLOSE 60*ATDC)I CALCULATE THE TIMING AT .050 TO BE INT OPEN 6*BTDC AND EX CLOSE 1*ATDC GIVING ME 7*OF VALVE OVER LAP AT .050 LIFT.TALKING TO THE EXHAUST MANUFACTURERS THEY SAY I WILL BE ON THE BORDER LINE OF HAVING REVERSION PROBLEMS WITH A SILENT CHOICE SETUP.THERE SEEMS TO BE LOTS OF PEOPLE GIVING ADVICE WITH REGARDS TO DURATION AND LOBE SEP.ANG. BUT I THINK THE REAL NUMBERS WE NEED TO BE CONCERNED WITH ARE VALVE OVER LAP AT AN EFFECTIVE LIFT AND THE TIMMING OF THIS OVERLAP PERIOD IN RELATION TO PISTON TRAVEL.ANY HANDS ON ADVICE WILL BE APPRECIATED. null[*]nullnull[LIST][LIST]

Bruce

Your thought process is correct concerning the overlap of a given camshaft, however, there is no perfect rule of thumb. Your cam is at the limit of what I would recommend for a silent choice application in a 454. The 110 LSA will make more slightly more torque but puts you more at risk for reversion. Your same camshaft ground on a 114 LSA will provide a margin of safety against reversion and likely perform just as well. Bottom line is, tie the boat to the dock, idle the engine in gear with the silent choice activated, then shut the engine down and remove a riser. If it's dry your OK, if it's wet I'd look to increase the idle speed or change the cam.