The dual fuel conversion is more expensive and requires comprimises when using either fuel....With straight propane the compression can be higher, more timing, more cam, more power! Went for a ride Sat. afternoon with a guy who has the straight propane conversion on his 460 Ford in a one ton, lots more power then my 460 on gas. Still searching for the "right" pieces for mine, sending a spare set of heads to the shop today for freshening along with some super hard seats and stellite exhaust valves. I'm doing the conversion on a 100,000 mile plus engine that needs to be freshened anyway, so the cost of the pieces needed to run propane will be more then offset by the gains in performance and mileage....

The numbers I played with showed the dual fuel conversion to be more spendy, less efficient, and a much slower return on the cost of the conversion. Also, because I'm doing this on a 1 ton cube van, I've got lots of room for a bigger tank, or even dual tanks so I'll have plenty of range and not have to worry about landing someplace that doesn't have propane. A bit of planning makes availablility a non-issue....