Spark plug

[cbodybob]

What spark plug are you running with your Speedmaster heads.

 

[Geoff 2]

Use the same as factory heads.

 

[cbodybob]

Use the same as factory heads.

Can’t won’t reach into combustion chamber. Need a long reach

 

[Geoff 2]

Then you need the long reach, probably with the smaller 5/8" hex: BCP5ES. These use a washer, not a conical seat.