[spuggy]

Just found this thread (again) while looking for something else...

Originally Posted by martinker

So guessing the 930.104.341.2R was used on the 3.0 and the 930.104.341.3R on the 3.3's. If that assumption is true then the 2R does not use the special alloy, since it has a "Y" stamping instead of the "RR350" like on the 3R.

It seems that various smaller "S" motor cylinder heads, 3.0 turbo heads and 935 heads had a "Y" designation cast in (same location where the RR350 is cast into 3.3 turbo heads). This indicated the use of "Y-alloy" - early911sregistry forum thread with pictures: Y-alloy heads? Your 2.4S has 'em

Wiki says "experimental series Y" alloys, aka "Y-alloys", were developed during WWI: Wiki Y Alloy.

Further development during the late 1920's led to the series of Hinduminium (High Duty Aluminium Alloys), aka the "RR alloys" Wiki Hiduminium - of which RR350 is a member.