Are 68-76 Johnson/Evinrude 18 20 & 25 Cylinder Heads the same?

[nixboatparts]

Hello,

The title says it all. Are 68-76 Johnson/Evinrude 18 20 & 25 Cylinder Heads the same? They look identical to me, are they interchangeable? Aside from parts numbers I don't see a difference, they look like the same casting,

 

[F_R]

Absolutely not. Compression ratio varies. And no, you cannot put a 25hp head on an 18 and make it a 25. OMC knew you were going to try that, and they have different pistons, among other things. Simply swapping heads screws everything up.