ngk buhw-2 vs buhw spark plugs for 90hp merc?

[wn6ngp]

I've got a 90hp elpto sn OT087666. Now I have the -2 plug in there but I see some non -2 plugs for sale as well. What is the difference between these 2 ngk plugs?

 

[Alumarine]

According to the NGK site the BUHW-2 have a .071" gap and the
BUHW have a .050" gap. BUHW-2 are recommended I believe.

 

[wn6ngp]

According to the NGK site the BUHW-2 have a .071" gap and the
BUHW have a .050" gap. BUHW-2 are recommended I believe.

My guess is that the .05 version is more for older ignition systems with less energy. 071 makes the voltage go to a higher value before firing which is good for new ignitions with lots of energy but if you have an older weaker ignition then the .071 would still go to higher voltage but the duration of spark would be less so it could result in less combustion. Oddly the one chart I saw on NGK did not list my 2000 90HP ELPTO but did list the older merc motors and it recommended the .05 for the older, which kinda makes sense. I dont think its related to the temperature rating of the plug like they do for cars.

 

[Texasmark]

My guess is that the .05 version is more for older ignition systems with less energy. 071 makes the voltage go to a higher value before firing which is good for new ignitions with lots of energy but if you have an older weaker ignition then the .071 would still go to higher voltage but the duration of spark would be less so it could result in less combustion. Oddly the one chart I saw on NGK did not list my 2000 90HP ELPTO but did list the older merc motors and it recommended the .05 for the older, which kinda makes sense. I dont think its related to the temperature rating of the plug like they do for cars.

I don't remember when and on what engines Merc introduced their 40kV (unloaded) plug voltage. Would assume the difference may have occurred at that time.

 

[Chris1956]

Not sure that gap information is correct. My '77 Merc 1500 called for BUHW, where my '73 Merc 850 called for BUHW-2. They both had the same battery driven CDI ignition system.

The BUHW-2 always looked to have a slightly longer electrode projection, but that is just a guess.

 

[wn6ngp]

I've got a 2000 model 90hp elpto and it came with -2. A friend has I think the immediate predecessor 90hp ~1998. It came with just BUHW. I suspect that transition in motors is when they increased the voltage levels and would have probably increased the wire insulation to handle the increased voltage.

The electrode is a surface gap so I'm not sure what you mean by longer. Do you mean the body of the plug? The distance between the center and the edge is the .070 vs .050.

 

[Chris1956]

If you put a straight edge across the end of the spark plug, it appeared the center electrode protruded a bit more, out of the spark plug.

It was a while ago, and my memory may be wrong, however, I do not think your theory of higher voltage and heavier sparkplug wire insulation is correct.

 

[Texasmark]

Not sure that gap information is correct. My '77 Merc 1500 called for BUHW, where my '73 Merc 850 called for BUHW-2. They both had the same battery driven CDI ignition system.

The BUHW-2 always looked to have a slightly longer electrode projection, but that is just a guess.

https://www.ngksparkplugs.co.za/wp-content/uploads/2019/01/NGK-Catalogue-2019.pdf

Page 241 of the NGK catalog.