Blanking plugs for convenrting twin plugged heads back to single plugs
 

Does anyone have a source for a blanking plug suitable for filling the second spark plug holes in 911 heads?

I have a set of heads I would like to use in a single plug motor (race series rule) but they were drilled for twin plug (a mistake by the shop that built them).

I am hoping for something better/cleaner than just leaving a unconnected second plug in them.

My first thought would be a threaded piece of aluminum with a small flange on the outer end to seal like a plug.
Maybe with a screw slot to tighten it?
They should be the same length as a plug.
You should be able to get a machine shop to whip you up 6 of them for a reasonable price.
Bob

When I did my rebuild I had my heads machined for twin plugs in case I wanted to twin plug in the future. I just put spark plugs in the second hole. Once the valve covers are on you can't see them.

John,

Any issues with hot spots/detonation?

I was hoping for something a little more elegant. I may have the electrodes cut off some plugs and then weld the ends up.

If your engine experiences heat-related detonation, that would affect both spark plugs, active or not.

For a suitable plug, you'll need to source a 14mm-1.25 bolt of the exact length. When tightened with a copper crush gasket, the end of the bolt should be exactly flush with the wall of the combustion chamber. Too short and carbon builds up in the exposed threads. Too long and the exposed bolt threads could create a source for pre-ignition.

I vote for a backup set of spark plugs installed in the twin plug hole. Easy no brainer. If you desire more elegance, buy a set of original Bosch 911S Platinum or Denso Iridium spark plugs; or a set of Splitfire plugs for conversation pieces.

Sherwood

No hot spots or detonation issues. I've got 2500 miles on it since the rebuild. Extreme heads did my heads for the rebuild. I asked them the same question. They suggested the spark plugs.