Liquid propane injection is already commercially available both in the USA and in Europe. The only way for automotive LPG conversions to meet current EPA regulations is with port injection and vapor injection is more commonly used than liquid injection.

Generally, conversions are done for economic reasons rather than for 1/4 mile drag racing performance. Actually, it is not the fuel that governs the performance of an engine but rather the amount of air that it can ingest. Propane's effect on full-throttle performance is that the propane vapor displaces more air in the intake manifold than atomized liquid gasoline. Once in the combustion chamber, all fuels must be vaporized before they can burn.