I know about extended plugs having some advantages with some engines, but I’ve never heard of it being used to raise compression.
While it must literally raise the compression slightly, by sticking something further into the combustion chamber, it’s probably not enough to make a noticeable difference.
Maybe they say it does because the extended tip creates better combustion process?
Just adding a comment. Sorry I don’t have any actual numbers for you. Never played around with the 170.
Good luck. And I think it’s a good kind of hijack myself. Talking about the plug gap, we might as well talk about the plug type as well.
Especially if there are any advantages to be had.