Ето ти пример от сайта на NGK (да, може да се обвинят, че е с рекламна цел, но по-добре като източник е производител на свещи, отколкото квартален майстор или John Smith от "форума на"):
http://www.ngk.com.au/spark-plugs/techn ... patibility
Цитати:
"
There are two critical factors that need to be understood when converting a vehicle from petrol to LPG:
LPG burns hotter
LPG increases the voltage requirement at the electrode gap
In an attempt to correct these two factors, as a general rule we suggest to:
Use a spark plug that is one heat range colder than standard to compensate for the increased heat from LPG"
Накратко - понеже изгарянето на пропан-бутан е с по-висока температура отколкото на бензина, добре е да се кара с "по-студени" свещи.
"
Reduce the electrode gap by 0.1mm to compensate for the increased voltage:
It is difficult to gauge exactly how much the voltage requirement has changed as other factors such as engine wear, loss in compression and ignition system weakness for example may provide an influence. As such the electrode gap may need to be adjusted several times until the correct gap setting is achieved for that unique vehicle.
Unless the vehicle is a production vehicle designed for LPG, the installation of LPG results in a modified engine. As such, it is the end users responsibility to ensure that the engine components have been considered and altered if necessary to allow for the modifications."
Това пък е относно електродните разстояния (не е съществено по темата - ясно е за всеки, че трябва лека корекция).
И все пак още от същия производител:
http://www.ngk.de/en/products-technolog ... ark-plugs/
Цитат:
"
The gas-air mixtures are more difficult to ignite. More ignition voltage is required and the risk of failure of the ignition coils increases. A narrow, laser-welded middle electrode with iridium chip which gets by on less ignition voltage counteracts this. In addition, the electrode distance is pre-set to only 0.8 mm."
Накратко - препоръчват иридиеви свещи при работа на газ заради по-ниския волтаж, на който работят и по-късото електродно разстояние.