conversion dealer and 1 magazine with no price on homeowner natural gas compressor. The limits of practicality have been exceeded except for the few that have more money than brains. As already proven and used in Europe, engine designed to % CNG is better. Conversions already exist in USA for % propane and % gasoline with simple dash switch and was practical with the tax incentives at the time. I drove an always heavily loaded 1 ton work van for many years in the 's with that conversion with zero problems with either system using 5 gallons of fresh gas every ~ 15 tanks of propane to avoid gas going stale. That used a stock Dodge and worked very well. No noticable difference between the 2 different fuels. Although very practical after the conversion made, without the tax incentives for the conversion like today, not economical to do conversion probably due to the DOT approved propane tanks cost that fit under van. No problem filling propane tanks like stock gas tank, but propane had to be vented a tad to know when full.