You need to be very careful going up beyond anything greater than a 2:1, 3:1 at most. You have to remember that at some point your multiplying force will be so great that you will bend something or break something if you are stuck or hang up on something. It would be a good conversation piece to explain how you bent your subframe though!!!!
Plus, the more multiplying force the less pull distance you get so you will need to move your anchor back further and use much more line. 4 feet of pull on the haul line will net you 2 feet of load pull in a 2:1. A 4 foot pull on the haul line will net you only 1 foot of pull in a 4:1, and so on......
Sent from my iPhone using Tapatalk which means there are more than likely spelling errors!