This has been around for a while. About 3 years ago I read an article about someone here in Jersey doing testing. If memory serves the cost was much more ($300) at the time.
It works by pulsing a valve and delivering a small burst of propane into the intake. The o-2 sensor sees the mixture as rich and then advances the timing to adjust for the condition. The propane apparently helps the gasoline to burn more effeciently without raising engine temps that advanced timing alone would do.
The system prolly works, the question being how well for your application. He states a 30% increase in the Omni, and a chevy 350, but does not state what the actual MPG figures were before installation in the unit. Could it be the engines were 'de-tuned' in such a way that the propane injection acted as a band-aid to correct for the de-tuning? :dunno:
The lack of data there leads me to believe that is the case.
Another thing not mentioned is the fact that opening and closing the valve will cause noise that can be heard inside the cab. (this from reading an article 3 years ago) This is why a switch is used to de-activate the unit. One would prolly use it on interstate trips where the buzzing noise would be worth putting up with, and the best mileage improvement would be seen.
He mentioned that some engine systems would not benefit without some kind of retrofitting. Could this be a reference to wide band O-2 sensors? If so this would affect more than 'a few' cars as he has indicated.
Buick Runner wonders if it is worth a try. Well I didn't see a money back guarentee, but if I had a modded T/R with big-ass injectors, drove a lot of highway miles, and wasn't getting the MPG I think I should, then I would give it a try.
What the heck if it worked out real well, you could relocate the unit to the trunk, and substitute a B-BQ grill sized tank for the little one and save even more money. As long as that is there, why not get a regulator and an electric valve and throw a propane injection in for performance! :cheers: