[octinum]

Originally Posted by cRiPpLe_rOoStEr

Direct injection became so prevalent on newer generation of turbocharged engines because it doesn't require such a very rich air-fuel ratio. Downside is an increase to NOx emissions, and even some particulate matter buildup which used to be previously seen as more troublesome to Diesel engines than to spark-ignited ones.

Right, missed that point. Though that's limited as well, I remember reading that small VW engines with both turbochargers and direct injection consume more than larger NA engines with similar output. However, this comment might be for an older generation TFSI.

Alfa Romeo JTS engines suffered from some soot buildup; long time users say equally maintained Twin Sparks (port injected) "keep" their performance longer than JTS because of this.

Originally Posted by cRiPpLe_rOoStEr

Either going through the evaporator or being allowed to vaporize naturally at the intake manifold, an amount of the charge air would always be replaced at a port-injection engine operating with LPG. With the cooling effect, there is a lower NOx emission, even though the AFR could still be leaner than with a vapour-phase injection.

You're on spot again. But fuel vaporized in the intake manifold would also help a denser charge, lowering charge temperature. The injectors could provide more fuel per cycle as well; as the vaporization would happen _after_ injection. I believe it would be beneficial in any case; better than vapor injection at least.

Originally Posted by cRiPpLe_rOoStEr

I have only found mentions to the usage of stock injectors for direct-injection engines. Port-injection ones may still require supplemental injectors only for the LPG, just like the 5th-generation CNG conversion setups.

I haven't found any references to supplemental injectors too. I have a feeling that the manufacturers never bothered with port injected ones when the trend is toward direct injection, and the extra cost for liquid injection tech would be harder to justify for an already mature market of port injected vapor phase kits.

This is not a problem for me though. I already want to be able to switch to "stock" when required, so I'm not touching the gasoline hardware. I want to play with the sequential LPG kit on my car. If anything goes wrong (short of a fire that is ), I want to switch to the virgin fueling system from the factory, at least until I'm safely home.