12 volt 1949 8BA flathead 8.

Petronix doesn't say anything about spark plug gap one way or the other. I assume I could open it up 10 thousandths or so but that's a guess.

Anyone have an educated answer?

 

I run an MSD distributor, and run my plugs at .030". Really no big improvement to be made going wider, it doesn't take much to touch off a burn with 7:1 compression, and typically a rich mixture. The wider the gap, the more load on the coil, too. I'd start with .025" (stock) and if you really want to open it up, do so slowly.

 

Agreed! Start with stock settings. Go up slowly if at all.