Spark Plugs

That depends on what's in there. If the heads are near stock, I think W7DC or W8DC. These (I think) are 14mm and short reach. These should be 19mm or 3/4"

But my engine has a 12mm long thread as the heads are welded. I run NGK DP8EA9. I think it's a 16mm socket.

My suggestion is to take one out, see what you have, and what the "business end" looks like, then post back here.

There is no way to give you any definitive answer unless we know where to start.

Thanks, I agree, but I cannot find a socket in my tool box that fits the plug in place and I have had old and new BMW's and Porsches.  Texted the engine builder to see what he used, but no response, that certainly helps.  I will see if I can locate a more complete set of sockets.  Thanks

CRM, I found myself in the same boat the first time I changed plugs. None of my spark plug sockets would fit. The engine builder had used heads that took 12mm plugs and the plugs he chose needed an 18mm socket. These are the (Denso) plugs, which I think are more commonly used on motorcycles. Go figure.

Couldn't find a spark plug wrench in that size quick enough, so I just used a deep socket.

Good idea, I will go thru some deep sockets tomorrow to see what will work.

Someone on here, I think, posted a trick for making a conventional socket grab and extract a plug. Can't recall what the trick was, though.

I eventually found an 18mm spark plug socket at Sears.

NGK plugs. 

Bosch does not make decent plugs anymore.

Mitch wrote: "Someone on here, I think, posted a trick for making a conventional socket grab and extract a plug. Can't recall what the trick was, though."

I've seen guys in paddock areas use a regular deep socket and as they get ready to slide the socket onto the spark plug they put a latex glove over the plug and push the socket onto both.  The glove material between the plug hex bottom and the socket helps grip the plug so you can extract it after you get it loose.  You just have to be careful that noting slips into the plug hole.