[citadel]

I've been thinking about this one too. As far as I know, this is more of a performance upgrade than an economical one. It should improve your mileage, but you have add in the fact you're using propane as well. I'm not sure how much propane you would use, but I'm not sure the amount of mileage increased (2 mpg or so) would offset the cost of the propane you will use.