Snowman,

The doggieness comes from the fact that LPG has less BTU (or Power) than does gasoline and that hasn't changed since both fuels were discovered. Most people would not notice much difference unless they are carrying or pulling a load, going up hill, like to accelaerate quickly, etc.

Also, due to the OCTANE rating differences in the fuels there is also a difference in the engine timing setting to optimize fuel combustion and prevent pre ignition (spark knock) when operating on one fuel or the other. With the new CARB Tier I thru Tier IV standards engine timing is not so easy to set (if at all) similar to the auto industry.

Yes, I have driven both in 41 years in the lift truck industry and have studied Fuel & Lubricants in pusuit of a BS Degree in Automotive Engineering & Technology. Meaning we read about then went to the lab and did test, tore em down, etc, etc.