I PURCHASED 1981 4 cyl. 1981 kaw 750 ltd. had been sitting 10 years,with no use,sitting without carbs,anyhow sincew my cousin went to work fo mobil,as a lube engineer,he has sold me on the synthetic,yes it is quite expensive,an I even had a crankcase full of gas from different folks trying to start ti with no prep work,but this (besides the 5.99 a quart has wored out great ,i am a believer in about every two thousand,an after two changes Ii pulled the top half of th emotor apart an could eat of the head surfaces,no deposits sludge,an the clutch even seems to be operating better.hope thos helps an of course this is one mans opinion.