Water Cooled Turbos

[Dave.Eaton]

can't resist a smile at the inclusion of sae papers in this context, but i
digress....

anyway, audi make the note in their paper on the v6tt that one of the issues
with water-cooled turbos is that the water will vapourise and can stop
coolant being drawn in by the after-run pump.  for this reason, the
after-run coolant flow is reversed (i.e. coolant is pushed to the turbos).
anyone know if the after-run pump "reverses" direction in the i5 20vt?

dave
'95 rs2
'90 ur-q
-----Original Message-----
From: QSHIPQ at aol.com
Date: Tue, 13 Feb 2001 20:49:23 EST

Grand and expensive misconception, that afterrun stuff, IMO.  Several SAE
papers indicate that there are great advantages to the water jacketed
turbos.
These advantages of watercooled turbos jackets can be found in several SAE
papers, most submitted without any *afterrun* function.  Dodge was the first
to use the water jacket on the center bearing in production car turbos (I
shy
from "watercooled turbos" per sae, Ned has a great story from kkk regarding
their insistance that *all* turbos are oil cooled).  They have submitted a
series of tests to SAE (mid 80's) wrt water jacketed turbos, dodge *never*
used afterrun in the 10year run of turbo 2.2t and 2.5t motors, which
outnumbers audis turbo production by several fold even today.  The gains
were
so dramatic, it was the saving grace of Chrysler/Dodge, since they needed a
v6/v8 performance without the investment, and warrantee costs associated
with
non WJ turbos.

As far as urq application, I have done several installs of WJ turbos with no
afterrun function, few customers really want to pay for the pump and
associated hardware.  And frankly, they really don't need to, the advantage
is putting in the WJ turbo, not really the afterrun function.
The pros in the context of urq's:
-  Better turbo life (see SAE 880258 Severe Turbocharger Bench engine tests)
wrt coking of the center bearing during operation and shutdown
-  The ability to delete the dual oil filter setup on the urq (redundant to
water jacketing)
-  less heat soaking across the center bearing
-  Post shutdown temps reduction is dramatic, especially at the piston rings