One of the downsides to attempting to add small amounts of propane to a gasoline EFI engine is that propane, as a gas, easily displaces the air entering. So not only does it burn up with some of the oxygen it also displaces more oxygen, unlike a liquid fuel that wouldn't diplace as much.
Of course if you can also get your hands on some cheap bottles of oxygen... Ummm... Never mind... Bad idea... Abort mission!
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