I'm confused by this thread. Crankpin asked about a Supertigre .61 bluehead. I see a lot of replies for the Supertigre .60 bluehead.

The .60 was a loop-scavenged beauty with side exhaust.

The .61 was a rear exhaust Schneurle-ported engine.

The .60 with PDP (Perry Directional Porting) was a real powerhouse.