I'm sure those are "advertised" durations, so take about 50 off and you'll have the "actual" duration. Most cams WITH actual 310 duration have alot more than .540 lift(usually over .600 somewhere). If I recall from back in the day, the "blazer" cam was not an RV cam. Remember back in the 80's when the ads in catalogs said "If you want the baddest sounding car in the lot.........buy the 305 duration cam"

I'm sure it had a "choppy" note to the exhaust, but everyone's idea of what a cam sounds like is different. It ain't a big cam unless the car shakes...not just the tailpipe!! LOL!