[Bob Goding]

Interesting thread as I have wondered about these numbers myself. I read in "911 and Porsche World" magazine
earlier this year, an article about the evolution of the 2.7RS by Paul Davis and Russell Lewis,aparently a couple of experts. Quote"--the 2.4 litre engine ,which forms the heart of the Carrera unit,has a crankcase manufactured in pressure cast magnesium alloy,used first on 2.2 litre engines--but then modified with internal strengthening webs supporting the mains bearing saddles and identified by the casting number 901-101-101-7R.
With the introduction of the 2.7 unit,this became the '102-7R'[with additional reinforcing]and ultimately the basis of all all Porsche production engines ,until the the Carrera 3 unit appeared in 1976----"Sounds OK to me .
I have a 76S ex US. so curiosity led me to have a look at the numbers---The engine type is 911-84 S/N 6561274 which appears correct and I believe is the original engine.
I also have another engine [The on-going never ending rebuild!]
which is a 911-85 S/N 6274937 and therefore is a 77[as it was supposed to be.]
But both of these engines have casting numbers 901-101-101-7R
on one half of the crankcase and 901-101-102-7R on the other half!
It seems logical to me that the 2 case halves would be different casting numbers --but what was the 102R previously?
Triva I know,but interesting nevertheless?