ok this might be a dumb question but whats the difference in a 3 bolt crank and a 4 bolt crank? does it just depend on the year or does it mean anything at all.

 

I don't think there's such cranks.

Perhaps this is instead in reference to the vibration dampers; small blocks installed in model year 1969 and earlier vehicles use three bolts to attach the pulley to the damper, 1970 and later use four.

 

yes the damper bolts thats what i was asking about. dont know what i was thinking when i said that earlier. so it just depends on the year and nothing else.

 

Yes it's just the year in production vehicles. Ford used to (and maybe still does) sell racing dampers that had both patterns in them, so some racing applications may still use the three bolt style.