[s-cars] Fwd: Turbo cooling 101

[Joseph Pizzimenti]

Long story short, we should all be cool and get HKS
Turbo Timers.

Riceboy

--- QSHIPQ at aol.com wrote:
> Not good information Phil.  Comments inserted...
> 
> SJ
> 
> In a message dated 12/30/2003 5:10:36 AM Central
> Standard Time, 
> quattro at isham-research.com writes:
> >All turbos are air-cooled.  The heat removed by
> liquids is insignificant.
> 
> No.  Get SAE 880258- The Development of a Severe
> Turbocharger Bench Engine 
> Test, 970922 - Development of Modern Engine
> Lubrication Systems,   860103 - 
> The 
> Third Generation Turbocharged Engine for the Audi
> 5000 CS and the 5000CS 
> Quattro.  All these SAE articles are co/authored by
> Audi AG, btw. 
> 
> There are basically 3 generations of the "K26 turbo"
> as we know it.  The 
> earliest generation (which excluded audis k26) had
> no oil spray in the center 
> housing.  Gen II (audi "oil coolers") had oil spray
> onto the center shaft and 
> shaft walls to cool the center bearing assembly and
> help prevent heat soak.  
> The 
> Gen III (current audi flock and latest k24/26
> designs) has Gen II plus water 
> cooled center bearing jacket assembly.  The design
> of Gen III was to help 
> prevent post down heat soak problems in the turbo,
> reduce temp spikes 
> associated 
> with high turbo loads, and to reduce the temperature
> of the piston rings 
> (running 
> AND shutdown function).  Even SAE 860103 (fig 9)
> shows significant reduction 
> of Piston Ring and Center housing temps with the
> addition of Water cooling.  
> 
> Trivia:  In the I5 turbo water feed runs at around
> 6-10L per minute thru the 
> turbo and the oil flow is 10L per min at 1000rpm and
> 25L per min at 4500rpm.  
> That seems a bit more than "insignificant" to me.
> 
> >On the 10V I5s, there are two carefully designed
> air passages that take 
> forced air from the
> >front grill and direct it down the side of the
> engine.  Some plays over the 
> turbo, some over
> >the exhaust manifold.
> 
> Insignificant IMO/E.  The best efficiency of a turbo
> runs the hottest hot 
> side and manifold (increase temp = increase
> velocity) and the coldest cold 
> side 
> (decrease temp = increase charge air density).  That
> means airflow is a mixed 
> bag.  I removed the euros and installed the quad 4 -
> 2 on ly 83 and the temps 
> of the turbo weren't significant.  The temps to the
> intake snout at the 
> airbox 
> was.
> 
> >This airflow is IMPORTANT.  Most of the turbo
> overheat problems I see have 
> occured >because
> >this airflow has been impeded - the most common
> culprit is an after-market 
> dump valve, >though
> >sometimes I find misguided people have put
> shielding between the manifolds.
> 
> Call me shirley... misguided.  FYI, the shielding is
> a great performance 
> upgrade if done properly on the 10vt non crossflow
> head designs.  It's there 
> to 
> reflect exhaust manifold heat off the intake
> manifold.  Significant 
> temperature 
> effects right where you want them, at the tip of the
> fuel injector.
> 
> >The later engines have a water jacket around the
> centre bearing.  This is 
> properly fed only >at
> >rest, after the engine has been switched off for
> around a minute and subject 
> to the water
> >temperature at the head union (where the water in
> the bearing jacket 
> convects to) >exceeding a
> >certain temperature.  The electric pump actually
> pumps water BACKWARDS 
> around the >circuit.
> >There is no meaningful flow in this circuit when
> the engine is running.
> 
> Not with you.  See above.
> 
> >The cool-down advice applies equally to the
> original and to the so-called 
> "water-cooled"
> >turbos.  There's absolutely NO WAY a pipe less than
> 1/4" in diameter can 
> carry enough >water to
> >deal with the kind of heat generated at the hot end
> of a turbo.  At least 
> two orders of
> >magnitude, possibly three.
> 
> Get the articles above Phil.  There have been
> several revisions to both oil 
> and water passages and placement to optimize their
> effectiveness in cooling.  
> The reason the pipes are small is because bigger
> isn't better, you want as 
> much 
> heat exchange within a small housing as possible.
> 
> >Equally, cool-down has to be done with the vehicle
> in motion.  Idling while 
> parked doesn't
> >help - the only underbonnet airflow in such cases
> is provided by the 
> alternator fan, and it's
> >pathetic.
> >--
> >  Phil Payne
> 
> 
> I disagree completely.  Cool down refers to taking a
> hot turbo and reducing 
> the temperatures of it as fast and as efficiently as
> you can.  Water cooling 
> after shutdown is only using half the available
> cooling, even with the 
> vehicle 
> not in motion.  Idle the car after a hot run is the
> best thing you can do, 
> regardless of underhood temps.  The underhood temps
> will never reach 
> 1400degrees, 
> so "aiflow" is insignificant to the objective of
> turbo cooling.  The airflow 
> is *less* with no motion, but so is engine load.  An
> easy trade, well 
> documented.
> 
> HTH
> 
> Scott Justusson
> QSHIPQ Performance Tuning
> '91 v8
> '84 RS2URQ Project
> '83 Urq
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