Theres a new LPG system recently introduced to Australia, it's called Liquid Injection LPG where the LPG is directly injected into the intake manifold/plenum, replacing the old skool mixer system where previously gas was transfered into vapour form then straight to manifold, reducing engine power out put and consuming 25% more gas.
Apparently the new system is not only more efficient and hi-tech but according to some dyno result, it pumps out more power than petrol.
Have a read through this.