Two-piece headers (manifolds)

[quk@isham-research.demon.co.uk (Phil Payne)]

> Is the two-piece for the MC only, ot does it fit the earlier KG/JY ?

> Kenn Thyrsted

Very curious.  Family pictures shows the n-part manifold on the page
that covers all 10V I5 turbos used in the ur-quattro.  Clicking on
the item numbers gives "no information available".  I thought they
had economised and re-used a drawing, but this seems not to be the
case.

Checking the 200TQ pages, the drawing is similar but all of the
information is there.  The n-part is defined for the MC and 1B.

Curiously, 1Bs came from the factory (I've checked five) with the 1-part
manifold otherwise listed for the ur-quattro engines.  I've never found
a factory-fitted n-part manifold on a UK car.  But if you try to order
a _replacement_ for a 1B (200TQ) engine, Audi immediately steers you to
the n-part manifold.

Hypothesis:  Audi thought the 1-part manifold would work on the
hydraulic lifter engines using MAC11/12/14 as well as it had on the
older mechanical lifter engines.  This proved (some time after
manufacture) not to be the case, and so replacement is steered towards
the supposedly 'better' n-part system.  Note my comments about the
Dialynx manifold - the problems seem to occur mostly if not exclusively
on hydraulic lifter engines.  It seems to be the same issue.  The
problem, to speculate further, may be that full throttle enrichment on
the later engines is turned off more rapidly when the throttle is closed
- it's entirely electronically controlled whereas the earlier system is
largely mechanical.  Overall, the MAC11/12/14 engines run leaner at
times than the earlier engines.  Closer to optimum, anyway.  I believe
that MAC-12D (MB/1B) engines in particular (no OXS sensor) suffer bursts
of very lean running and high gasflow when coming off WOT.  We currently
have three failed MB manifolds on the workshop floor and the failures
are IDENTICAL - so much so that we can't tell them apart.  And just to
piss everybody off - John Robinson's MB has utterly destroyed the front
section of an n-part manifold.  I've already shared the .jpeg with some
of the gurus on the list.

--
 Phil Payne
 UK Audi quattro Owners Club
 Phone: 0385 302803   Fax: 0870 0883933