This is quite a common conversion in Australia, well diesel and propane.
You only add 20% propane/80% diesel,veg oil.
The conversions cost about $4500 installed, but our govt gives a $2000 rebate because the cleaner burning produces less emmissions.
Apparently, depending to who you talk to, you get up to 40% increase in power and torque.
I know of one semi (truck) who rund a Cat c15 550hp and put it on gas and it now dynos at 600hp.
Neale