Gday, the LPG conversion on a VS V6 will slow it down a little bit (a lot more noticable than the V8). The do tend to run smooth but you have to keep your ignition system in top condition otherwise expect the odd backfire which will blow the air box to pieces. However you can fit a one way valve or flap onto this to prevent damage - a lot cheaper than replacing the box each time. For a full conversion with new parts you'd be looking at about $1600, and in WA you get a $500 rebate, not sure about other states though. My brother got his VS ute converted to LPG and gets about 400km from 60L of LPG, which is isn't the best economy but still probably 70% the running cost of petrol. He's burnt out one fuel pump from letting the petrol run too low in the tank ($120) so it can be quite costly in the long term if you arent careful and keep the maintenance side of things right up.
You can get a second hand kit from the wreckers but it is law to change all the piping - service line, fill line, vapour line etc. So the only parts you can get are the tank, mixer, converter, computer, and solenoids. Not worth going to the trouble of removing the service line from a wreck as its useless anyway, except maybe offcuts for something else. It won't pass the pits if they see second hand wiring used. In WA you still get a $500 rebate so a second hand coversion can end up costing nothing or very little if you get the tank etc at a good price.
If you work out the economy at 400km per tank/60L , that works out to be $9/100km (at 60c/l gas)
For petrol estimate 500km/60L thats $13.80 per 100km with petrol @ $1.15/l
Just approximate figures but gives you a ballpark figure anyway. I've had 3 cars on LPG and never had any problems, as long as you can understand the system and how it works it usually won't let you down.
hope this helps
