I have had two vehicles, one car hauler a one ton Dodge truck with a 318 Poly motor and a class A motorhome. I added the propane dual fuel conversion to the car hauler in the late 1970s due to the gas crunch, not being able to buy gasoline in some towns at night and the propane tank held 82 gallons of fuel. Propane does not have as much latent energy that gasoline does so you have to use more propane to make the same HP, just like alcholol The motor home was a pig on propane so I switch it back to gasoline only, the truck burnt two exhaust valves shortly after the conversion so it was not as good as I had hope for There was a 1968 or 1969 Charger that ran at the Winternationals around 1973-76 as a exhibition car on Saturdays severl years in a row, but it was not a class car and didn't really run very fast, high 11 s to mid 11s if I remember correctly. I'm sure it was Hemi powered, it may have been a school car project for one of the SO CA junior colleges Maybe someone with a better memory or someone that was involved with the car will chime in I have heard that some of the deisel truck guys use propane injection for a power adder , or maybe to cool the inlet air down