I think I saw on the Internet they were worth 25 horsepower per plug. Or maybe it was a dyno test write up in a racing ragazine.

1970 Duster
Edelbrock headed 408
5.984@112.52
422 Indy headed small block
5.982@112.56 mph
9.42@138.27

Livin and lovin life one day at a time