Steel head studs

[MrScott]

I've been reading up on head studs in preparation for my 3.0 rebuild.

Conventional wisdom says steel is fine for lower head studs in a street engine. If that's the case, seems silly for the factory to have gone through years of iterations of Dilavar studs when the steel version was readily available.

I'd think the consequences of a mismatch in expansion rates would be easier to test in a lab than susceptibility to rust over repeated cycles of expansion/contraction.

[Steve@Rennsport]

MrScott,

No shortage of opinions on this subject,.....

Porsche used steel studs as well as two generations of Dilavars in these engines with the intent to maintain even clamping forces on the heads through the entire range of expansion.

What they found is greater expansion with the larger bore (3 litres+) engines compared to the early smaller ones, hence the need for the Dilavar alloy which expands at the same rate as the other alloys used in the case, cylinders, and heads. The 3.6's used all Dilavar studs as these had larger coefficients of expansion.

You're right: it is easier to test such things in a lab and on a dyno to measure expansion rates and head torque and thats precisely what they did and how the Dilavar alloy was developed. Trouble is, its difficult to accurately simulate 100K+ miles and the world's environmental conditions to determine long-term resistance to corrosion,....

They learned a big lesson and thats why the late 3.6 Dilavar head studs have been so successful; they maintain consistent head clamping forces without the corrosion issues of their predecessors.

Now comes the opinion part,... ,....we use the late Dilavars in all 3.0 & larger engines for the same valid reasons. Nothing else works as well and while not cheap, they are VERY reliable.

Hope this helps,

[MrScott]

You recommend it, Porsche obviously saw a need for it, good enough for me. Definitely helps, thanks.
And I'm assuming "late 3.6" is the 993 version I've read about.

[Steve@Rennsport]

Originally Posted by MrScott

You recommend it, Porsche obviously saw a need for it, good enough for me. Definitely helps, thanks.
And I'm assuming "late 3.6" is the 993 version I've read about.

You're quite welcome.

Yessir, those are black-coated all-thread ones.

[ertech]

what studs did a 89 930 have ? the bad divilar's??or the updated divlars?
Thanks

[Steve@Rennsport]

Originally Posted by ertech

what studs did a 89 930 have ? the bad divilar's??or the updated divlars?
Thanks

Those had the first-generation Dilavars which are prone to corrosion.