Written by: Drew Mason
Hopefully a useful spark plug related post
I recently had a challenge to find spark plugs that would get over a major floor in my Weiand FR head’s design. After reading on this and not finding a solution I was happy with (the regular solution was to open up the threaded hole with a carbide burr to expose the spark on normal 1/2 deep plug
The plug thread depth on these heads was increased to 3/4″. With the valves coming close to the end of the plug thread I was struggling with getting the spark plug as exposed enough as possible to give a good spark, but without the ground strap hitting the valve.
The standard 1/2 plug meant that the tip of the ground strap was sunk well into the threaded hole, and a standard 3/4 plug meant the ground strap would hit the valve. This was also the case for the slightly rarer 5/8″ long plug.
The tip (ground electrode) on a normal plug hangs out of the end of the plug by about 3/16, which was really causing me an issue.
The solution – A ‘Surface Discharge’ plug – This meant I could run a 3/4 long thread, bringing the end of the plug about flush with the inside of the chamber, but with no protruding tip that would hit the valve. The spark jumps sideways, giving the best possible spark exposure to the mixture that I could find.
I used an NGK BUE 2322 plug
Hope this helps someone, at some point!
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