Exhaust manifolds, MC1/MC2/KH/UR-Q

[QSHIPQ at aol.com]

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Way oversimplified IMO/E.  Most chipped cars will find signs of EM cracks
even with fantastic motor mounts.  Cracking also occurs *within* the
manifold, specifically at the collector on cars that have been run hot and/or
lean.  Manifolds without support are more prone to heat/stress cracking than
ones that aren't, regardless of engine mount condition.  Unfortunately, the
5kt/200t are the ONLY audis I5's built that don't have support for the turbo
and/or EM.  The early urq's did, the later S cars did, the 20v N/A cars do,
the 10v N/A cars do.  If you look at Corky Bell's book on page 126, you can
easily see the problems with a long log style manifold vs heat.  He lists
expansion rates of .1in/ft for your typical cast iron log manifold.  He also
suggests considering two piece manifold designs to address the problem.  Yes,
a weak mount can exaserbate the amount of stress placed on the manifold, but
it is hardly the only culprit and reason for cracking.

I don't share the same batting average as you wrt motor mounts "causing"
manifold cracks.  Audi followed solid engineering practice in going to the
2pc manifold design, but stopped short of a good support for the
manifold/turb.  Then in a simplified and more retroactive engineering design,
they went back to the single pc manifold on the urS car.  The urS cars use a
single piece exhaust manifold that equalizes heat, centralizes the WG, and
they put support to the turbo.  I've done plenty of motor mounts on S cars
that carry the same part number as what you reference below.  Haven't seen a
cracked manifold  on an urS car yet.  Why not, if what you say is gospel.

Phil you are way off base here, in practice, theory and application.

My .02

Scott J


Phil Payne writes:
>Not yet seen a cracked manifold over a good engine mount.  So far the score
is >100% - fit a good engine mount, make sure it'sprotected (Type 85 -
heatshield, Type >44 - air duct) and your manifold won't crack.Solve the
right problem - don't mess >with exotic fixes for the symptoms without
dealing with the cause.