[Mr Gazza]

I think the 100bhp per litre benchmark was a holy grail that was being pursued just pre war in the late 30's.
500 singles were being developed in many Countries for racing and were nudging 50bhp by 1939. I think it was AJS that actually achieved it.
After that things were never the same and it wasn't until long after the war that power figures reached the same level in that class again.

It does seem somewhat nonsensical though, when the mighty Vincent was considered to be so powerful with a heady 55bhp @1000cc.

It also seems very disproportionate with much higher power per litre being achieved with small engines.

I always took it to indicate the efficiency of an engine, but as Dirty commented, it's probably just a guide to character or state of tune, and now just an old fashioned way of looking at it, which is way outmoded and out of date?

Is the Mito meant to look a bit like a 916 by any chance?