general argument is that LPG produces less tourque across the rev range--so reduce cam timing to get more tourque.

but all that does is reduce the air flow[volume] and if you use a vapour LPG system then you get less burnable fuel.

or you can fit a wilder cam with extractors and rev the engine harder using gears to create tourque at higher rpm.this will use lots more gas.

turbo or liquid injection is different story.