Cylinder head bolts, torque

[Drew20]

Hesitant about posting this one, as I know it's been covered plenty times already. A slightly different take on a very familiar query.
Haynes for E3 states final torque of 49-52 lbft, no angles, no re-torque
Haynes for E12 says 56-59 lbft, again no angles or re-torquing
A reprint of an E3 & E9 owners workshop manual states 52lbft, again no faff
BMW's own tech guidance from 1983 states 59lbft plus 25 degs after running the engine up to temp
Various posts on this site state similar, but with 35 degs final stage
Latest and greatest from this site states M12 bolts (mine are M12) get 100Nm (74lbft), with no subsequent angle

I am wondering why the large range of final torque answers? older sources have a fairly mild final torque whereas more modern sources have far greater final stage torques. Is it that gaskets have changed? Or is it simply more experience of head gaskets, bolts and the heads themselves?

Cheers

 

[Honolulu]

Suspect what you're seeing is the emergence of angle torquing between the E12 model shop manual publication date and 1983, and maybe some later improvements in metallurgy that made the bolts "stretchier" (i.e., higher elastic modulus).

Haynes (and Clymer?) probably used whatever values were stated in the factory manuals current as of their publication.

 

[HB Chris]

I use 55-60 ft-lbs on the m30. I know it doesn’t feel like much but it works.

 

[adawil2002]

I use 55-60 ft-lbs on the m30. I know it doesn’t feel like much but it works.

55 ft-lbs on the M10 as well.

 

[Drew20]

Suspect what you're seeing is the emergence of angle torquing between the E12 model shop manual publication date and 1983, and maybe some later improvements in metallurgy that made the bolts "stretchier" (i.e., higher elastic modulus).

Haynes (and Clymer?) probably used whatever values were stated in the factory manuals current as of their publication.

Yes, I was wondering if it was a change in materials. I hadn't thought of the bolts though, I was thinking of the gasket itself perhaps being able to withstand more pressure. Bolts could also have been improved.