Which vehicle variable?

Maybe I got the term wrong. so I was building in a sandbox when someone let out all these annoying boxes called chopperman which happend to be physical. Well 2 other people who were working on a house nearby rezzed bulldozers and started pushing these things off world. I join the fun after adding a bulldozer plow to the freebie FedEx truck in my inventory. Later on I am building when someone sets up these green and pink blocks which fall all over including a couple on my platform. Anyway these appear to be physical but appear to have more mass then the others. So I was wondering what I would add to a vehicle script to give it more pushing power, adding forward speed does not help.