*This has all been re-writen!!* I later installed these plugs in some engines & had some problems...
Ok... I got some comparison pics today of three different heads I have & the NGK B6HS (short) & NGK B6ES (longer) plugs in them.
First is a (older) Raw 'center fire' head that shows the difference between the short & long plugs... *edit*...The longer plug is too long & will hit the piston.
Next is a older Raw 'slant' head with a NGK B6HS (short)... The combustion chamber is much smaller on this head putting the spark plug much closer to the piston top, (& the reach looks perfect)!
I didn't even bother taking a pic of the longer plug because it was soooo far out that it was very obvious it would hit the piston.
& last is a new Raw 'slant' head (Grubee style) that shows the difference between the two plugs... These heads have a extremely small combustion chamber with more threads for the plug... (the longer plug fits perfect)!!
This is what i had on my bike for the Venice ride last Sunday... I rode more that 37 miles (much of it at WOT) with great success!
*Edit*... The engine i used this plug on was older Raw engine with a new grubee style head; it worked on this engine, but when I used this plug on a all grubbe engine the plug touched the piston. so I added a couple of extra crush washers to the new plug & then it worked good.*
So there you have it... Some heads will benefit from the longer plug & others will cause major problems. (I learned a lot from this)!