Re: Spark plug requirements
Originally all plugs were of the conventional exposed electrodes types. In time 2 stroke OB designers, both OMC and Merc found that under certain operating conditions a surface gap (no exposed ground electrode requiring a specific gap) plug performed better.
My owners manual specifies both types and after having tried the non surface gap, I am back to the the original style SG plugs.
In testing my plugs I found that the SG plug had a thicker and more pronounced arc and that may be due to the fact that the gap is like .060" whereas the conventional is .040 give or take....don't remember but it is less.
In the energy transfer equation, the wider the gap the higher the voltage required to jump it. Energy developed is the square of the voltage so doubling the gap could get 4x the energy in the spark and with a fast rising voltage you can run a set of SG plugs for 10 years and never have to change them. I ran the plugs in my 115 tower for 7.
My 2c,
Mark
