I am sorry to disagree. Back in those days I was very meticulous about getting the torque to spec (although today I do use German torques on my comp cam intake; Gudentite
).
I know my torques were not off back then. I feel quite safe in ruling out torque as an issue, well, in my instance anyway.
Michael you are right, the phenolic should have a pretty low cte. That is the problem since Al has a fairly high cte (coefficient of thermal expansion). The cte mismatch is what causes
residual stresses with heat. All of those residual stresses would be taken up by the phenolic, except where the Al is thin (at the fwd & aft feet). At these feet the Al would be able to cool slightly quicker(which creates some level of stress in itself), and leave the heated phenolic (because of its larger, and more insulated mass, in that region) to act upon the small feet. The residual thermal stress is cyclic with every use of the motor, and Al is absolutely horrible when fatigue cycled. (Adding heat to this region would add similar stresses to the same area)
Basically the problem exists because the central mass of the phenolic/Al does not cool very quickly, while the fwd/aft feet cool very quickly. This is acceptable when bolting the Al upper to an Al lower, but when you add in the thermally stable compund more residual stresses are left on the fwd/aft feet.
The more I think about it the worse the cobra manifold design looks.
Sorry for being long winded, but I usually am
. Hope it made sense, as beer and engineering principles don't generally mix.
Feel free to disagree, as this is just a theory of mine. I have taken no steps to prove my hypothesis.
jason
