An engine converted from petrol to L.P.G. (liquefied petroleum gas) will cause a change in the spark plug operating conditions. Therefore, some consideration should be made on the type of spark plug being installed.

As L.P.G. has different properties to petrol it influences the spark plug operating temperature and required voltage. The extent of this influence can be seen when comparisons are made on spark plugs which were fitted in an engine using L.P.G. and petrol.

Typical results are as follows :

1. Spark Plug Temperature

Temperatures are higher with L.P.G.
compared to petrol. This occurs due
to L.P.G.'s reduced cooling effect.
2. Spark Plug Required Voltage
Required Voltage

Required voltage increases with L.P.G.
because of the difference in the bonding
of gas particles between the two fuels.


To eliminate the influence of L.P.G. and to obtain optimum spark plug performance, NGK recommends:

-The use of a spark plug with one heat range colder (if possible) than that listed in the catalogue: eg, BPR6EFS-13 (L.P.G.) instead of BPR5EFS-13 (petrol) for VN 6 Cylinder Commodore.


-The reduction of the electrode gap by 0.1 mm (which lowers the spark plug required voltage)