Dave

Thanks. You mentioned perhaps the biggest reason a housing with leading
dual plugs should be designed from the get go. That is the force of the
combustion event against the threads. This explains why the current
housing plug boss design is so robust. It also explains why there is a
little half moon ridge near the plug holes on the outer housing.
Beefing up the housing to account for loss of strength near the large
breach no doubt. I suspect but haven't confirmed yet that there is a
stainless boss welded to the outside of the liner near the plug hole.
That would make sense because the flame propagation starts there. Nut,
screws and bolts !%#`!

Next idea. Common ground Y shape Siamese twin plugs that fit into the
present 14mm hole.

One less hurtle or one more concern

Doug in Japan

Sorry Doug but wrong! The robustness of the plug boss isn't to protect
the threads. It is because you need a castable boss there and to
reinforce the side of the ROTOR HOUSING against the HOLE being put
in it. The threads are fine, in fact engines seeing higher combustion
pressures than we will EVER see, AA fuel dragsters running 90% nitro
use standard plugs, just very cold ones.
Bill Jepson