Crack on manifolds

[QSHIPQ at aol.com]

 >The urS4 uses the exact same motor mount, and it fails
> regularly without manifold cracking.

>>No, but it's a completely different design.  You might as well say
manifolds don't >>crack on Harley Davidsons.

The overall length is the same, it's single piece.  It's designed to have
even distribution of heat, AND it's supported properly.  Without question the
2pc design would be better, it's just not necessary if you support the turbo.
 Which indicates to me that 10vt cars would do really well with support to
the sea anchor hanging off the right side of the motor.

> I expect that all 5k/200/urq's without manifold/turbo support will cause
> manifolds (single or 2pc) to crack, some faster than others (as you noted)

>>Not happening here.  I have dozens of personally fitted single-piece
manifolds >>running round the UK, some on daily drivers, and no
>>complaints.  I've never refitted a support bracket to an MB (despite ETKA,
you >>don't usually encounter them on MBs) and there isn't
>>one either on my MB ur-quattro or on the Bus - which runs a damn sight
hotter >>than stock thanks to SJM.  I discard them on WRs
>>unless the car is a 'Concourse' car.

I fit a lot of single piece manifolds here too as well as 2pc.  They all do
well with heat cycling then machining flat.  Still prone to warping if there
isn't a good fit to the exhaust studs.  You can't argue .1in of expansion/ft,
especially if you don't have room for it.  No question in my mind that the UK
has few support brackets, I'm sure that has to do with RHD fitment.  That
doesn't at all mean it's not a good idea, anything you can do to support that
anchor helps, better would be supporting the turbo itself.

> Why don't the 20vt motor mount failures cause cracking?

>>Because the 20V engine has a completely different moment about its own axis
- the >>20V head adds mass on the left of the centreline,
>>not only for itself (including the second cam) but also because both the
inlet >>manifold and the cooling manifold are to the left of
>>the centreline.  This is incredibly obvious as you crane a 20V lump into a
car - the >>balance is completely different to a 10V.  Not
>>only that - the 20V exhaust system is laid out COMPLETELY differently and
the >>moments between the major masses (turbo, wastegate)
>>and th emanifold are a fraction of what they are on a 10V.

The 20vt is supported, period.  The heat is more even distributed in the E/M.
 That said, exhaust temps are the same on audi I5 20vt vs 10vt Phil, many
have measured them.  Which means that a single pc 20vt is prone to cracking,
it just doesn't.  It's quite obvious to me why not.  It also indicates that
with all this "moments between the major masses" (?) means that support of
the 10vt cars is even more critical.  Let's look at the manifold and turbo,
not the motor mount.  Motor mount failure is a constant, the variable is
manifold cracking.

Proper support of the single or 2pc design of the 10vt cars is a good, no
*great* idea.  Motor mount failure is a constant (cronic) problem, but hardly
eliminates the solid engineering application of good weight support of a hot
EM

Thanks for your opinions Phil.  I suggest a quick read of Corky Bell's book
for starters, he's opinionated too, and describes exactly why 10vt crack, why
2pc manifolds, and without nary a mention of motor mounts.


Scott J