Head Bolts and Exhaust Manifold Studs

Killer6 said
No, torque to yield bolts came into being in the late '70's, and prominence in the '80's, due
mainly to the use of aluminum cyl. heads. The increased expansion of aluminum would
eventually crush the head gaskets to the point they wouldn't be able to recover & hold
a seal. The fix(now combined w/MLS gaskets), was to use longer bolts that were torqued
'til they were floating between elastic & plastic deformation, thus not increasing the load
on the gasket as much w/the high amt. of expansion. The bolts on your slanty can be
used to infinity really, unless they have been damaged,corroded,or over-torqued by an
appreciable amount.

Makes sense... but not all head gaskets get crushed by non-TTY head bolts. All the Mitsu 1.6 and 2.6L engines I built re-used the original bolts, which were not TTY types (as far as I know; they never stretched), and I then went to ARP's on the 2.6 turbo engines with no gasket problems. I suspect the reason to go to TTY was to get more consistent clamping pressure with the bolt yielding at a consistent point on the curve, rather than depending on a thread resistance caused torque giving consistent clamping.