Small Block & Big Block Chevy Specific - Why are my spark plugs arching out of the boot?

my dad has a 1949 Ford Sedan street rod with a 1970 Chevy 350 in it. the pugls are arching or somehting out of the boot. when you turn the lights off you can see light at the boot. we just replaced the wires thinking that may be the problem. What do you thik this is?

Thanks
Jesse

yea i had the same problem on my LT1 but I replaced the plugs wires and it went away. It was like a light show under my hood at night....lol :)

A weak spot in the boot, a lot of buildup on the spark plug, it's too close to the header tube, or any combination of those might make the current arc to the header rather than travel through the spark plug.

Maybe the ceramic of the plug has a really small crack in it.
Caleb

The bottom line is that it is electrically easier for the spark to go that way than to jump the sparkplug arc. A weak spot in the boot, a lot of buildup on the spark plug, it's too close to the header tube, or any combination of those might make the current arc to the header rather than travel through the spark plug. These are the most likely causes.

You might need the ceramic sparkplug wire connectors if a regular boot is too close the the header or manifold.

Or there are OEM heatshields that can be adapted to help.

Jim