How Many Spark Plugs?

[COOPS]

Just had a call from the mechanic who is servicing my Mercedes C240 (straight six) and he has advised me that it needs new spark plugs. This I am told will take 2 hours to do and will require "12" plugs. I asked the question as to doesn't a six cylinder only need 6 plugs but was told the C240 has two plugs per cylinder
Can anyone confirm this or am I being ripped off
Many thanks
Glenn

[MR2Mike]

COOPS said:

Just had a call from the mechanic who is servicing my Mercedes C240 (straight six) and he has advised me that it needs new spark plugs. This I am told will take 2 hours to do and will require "12" plugs. I asked the question as to doesn't a six cylinder only need 6 plugs but was told the C240 has two plugs per cylinder Can anyone confirm this or am I being ripped off Many thanks Glenn

The C240 does have two spark plugs per cylinder.

[COOPS]

Many thanks for your spoeedy reply, you wouldn't happen to know why it needs two? Efficiency? Is this common in todays cars?
Cheers
Glenn

[deltaf]

Gives a better burn due to initiation of two flame fronts!


>> Edited by deltaf on Wednesday 20th August 10:35

[MR2Mike]

Not exactly common, although Alfa Romeo have made their "Twin Spark" engine for years.

Two spark plugs have been used in aero engines for a long time, but simply for reason of redundancy. In a car, it's for reasons of performance. As deltaf says, two spark plugs located a reasonable distance apart will inititae two flame fronts which will cause the compressed fuel/air to burn more quickly. Faster burning means more of the heat energy is used in expanding the gasses/pushing the piston down rather than be absorbed by the engine block/head/piston.