[urq] Water Cooled Turbos - should be water jacketed turbos

[QSHIPQ at aol.com]

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

The cons in urq context:
-  you are adding another heat sink to an taxed cooling system.  Make sure 
your radiator is clean and has no hot spots, and you have *all* coolant ducts 
installed at the radiator
-  The coolant tends to get air trapped at the aux rad input vent (the really 
small hose from the aux rad to the main rad) and the upper hose, this can 
lead to overheating quite easily if the radiator is marginal, or you allow 
your antifreeze level to drop.  
-  The install requires that a freeze plug be removed and the one with the 
outlet installed on the engine, not an easy job.

Personal datapoint
Bob D runs the 87 thermo in his 84 with one of my modified k24 units, which 
with full air conditioning regalia only tends to heat creep with a/c on in 
traffic at low speeds
My '83 runs the 80C thermo (A/C delete) with a early MC k26 WJ unit, and aux 
rad delete.  Head temps run in the 190-210 range always (including track use)
Neither car uses the afterrun function on the turbo

If you take a gander at the print wrt wj turbo center bearings, the *main* 
advantage to them *isn't* afterrun function, it's hot run/low speed and 
shutdown function.  So those that don't want to spend a fortune getting a 
good afterrun pump, have no fear, the SAE papers are with you, and in fact 
you can have almost equal the shutdown temps, if you drive easily or idle 
down for a minute or so before shutdown.

So technically Phil is correct, the afterrun's purpose in life begins on 
shutdown.  I might just add that it's purpose in life is a bit of an 
overkill, the advantage of water jacketing turbos is much higher before the 
afterrun's purpose in life.  I applaud audi for including it in their turbo 
cars (no one else has this many blades spinning post shutdown), I question 
the *necessity* of it in a WJ conversion of an older turbo car.

Even if you want to use audis own tests on WJ turbos (SAE 860103) you can see 
that *at* -1min thru 0 time the piston ring temps are 80C cooler with just 
the water jacket (by definition, no afterrun).  The peak rise is within 2 
minutes of shutdown regardless, so I really doubt the afterrun is really 
doing as much as most think.

Those that have broken pumps and don't want to spend the money fixing em, I'd 
say let your car idle a minute or two after a hot run.  Those that have the 
older non jacketed turbos, will find better turbo and piston ring life with 
them, regardless of afterrun function.  Save your money, install a bypass 
valve @ 30bux, the turbo will last longer, and the results measured in 
peformance gains.

HTH

Scott Justusson
QSHIPQ Performance Tuning
Chicago IL
QSHIPQ at aol.com
'84 RS2URQ - 20vt no afterrun
'83 Urq -k26 no afterrun
'87 5ktqw - leaking pump bypassed

As far
In a message dated 2/13/01 6:32:10 PM Central Standard Time, 
isham-research.freeserve.co.uk at pop.pol.net.uk writes:

> > I was replying to an earlier post off line and I realized that the much
>  > coveted water cooled turbos might not be that much better than the stock 
> oil
>  > cooled one if you do not include the afterrun cooling system in some 
form 
> or
>  > other ... at least I think that if my car had this sort of a setup I 
would
>  > still cool it off for a while before shutting the engine down ... 
thoughts?
> 
>  
>  Wouldn't have thought it any use at all without the extra sender,
>  afterrun controller and so on.  The auxiliary pump's purpose in life
>  starts when the engine stops.
>  
>  --
>   Phil Payne