LPG is not for a cossie.

But apart from that there are systems that are more powerful on LPG then on petrol but the old LPG system aren't

The new systems like Vialle LPI have the same power output as one on petrol because the LPI system is liquid injected. LPI is Liquid Propane Injection
The older systems aren't liquid and that's the loss of power.

But i agree with RS_Gus and Cosworth3dr, only for forlifters and cooking