Plug seat for GN1 AL heads

[vacuum 6]

What type of plug seat can the GN1 heads accept? Tapered or flat counter bore (washer type/gasket type)?

Some run Autolite 103s/104s (tapered) while others use Autolite AR39XX (washer type).

 

[DR BOOST]

they can use either style

 

[vacuum 6]

So the plug holes have a big flat bottom with a small tapper?

 

[DR BOOST]

yes

 

[ek02]

The only plug besides the Autolite 103 and 104 that has a tapered seat and the correct thread length for GN1 heads is the Autolite AR474 or AR473. They are very cold side electrode race plugs.