[200q20v] intercoolers

QSHIPQ at aol.com QSHIPQ at aol.com
Thu Dec 6 08:56:58 EST 2001

Bernie, comments inserted below
In a message dated 12/5/01 11:10:29 AM Central Standard Time,
b.m.benz at prodigy.net writes:

>My point of this additional reply is that IMO the participants to this
>thread have been hung up on the advantages of minimumizing pressure loss
>across the IC to the point of total exclusion of any charge temperature

It's both.  Pressure loss is a problem using long core IC's.  The most
efficient IC's have short cores, lots of frontal area.  There is little
"controversy" or debate on this issue, really good IC's are designed this
way, which results in low pressure losses, and high IC efficiency.   Pressure
loss on IC's is a concern because you easily can offset your "intentions" by
increase turbo outlet temps at the expense of IC outlet temps.  Pederson is
"hung up" on getting more and better, which is tough to do, cuz audi has
less, but really good.  TE is a tougher animal to tackle (given the choice)
because heat soaking IC's results faster, and with the same IC efficiency,
higher inlet temps means higher outlet temps.  I'm hung up on PD too.
Remember, audi computers are looking for boost pressure AT the manifold,  the
computer doesn't care what temp and pressure  is AT the turbo outlet.

>Scott, at least you understand that charge temperature
>reduction is the ONLY justification for intercooling.  Apparently, others do
>not, and thus may be misled by the fanatic few.

Pressure loss, Flow and Temp are all reasons and justifications.  You need x
cfm to make x HP, you want the turbo outlet/IC outlet pressures to be the
lowest differential, AND make the IC temp outlet the lowest possible.  You
are only correct above, IF the car doesn't have an IC.  If it has one, and
you are looking for "better/more", you have 3 concerns and 3 justifications
in design and execution.

>IMO, Audi is reverting back
>toward this extreme by designing cars for short burst performance, relying
>primarily on the transient, heat sinking capabilities of the forced
>induction system, rather than on the steady state cooling capabilities of a
>good intercooler design.  (Don't knock Macs, trucks nor computers.  Both use
>the best of ICs.)  What sells in volume is what the customer can use on the
>street.  That statement pretty much holds for most aftermarket upgrades

I'm not with you here.  Audi specs great IC's, you really can't find anything
in any respective size aftermarket that comes close.  And they work really
well, if you do your calculations based on the STOCK boost, flow and temp
parameters.  The problem with these small IC's is that they have very narrow
working ranges (tradeoff) as far as boost limits before pressure drops and
heat soaking.  Small hot turbos don't help here either.  Mac trucks?  Sure,
you've got the frontal area, go for it.  We don't.

>Scott, your flow/PD calks are well and good, but are only a part of the
>story if you do not consider the heat transfer characteristics of what you
>are proposing.  Good heat transfer from the fluid to the tube requires
>turbulant air flow, and therefore high velocity, exaggurated by the
>straightening vane effect of the fins within the tubes.  If one reduces the
f>low velocity by the addition of excessive parallel tubes to the point of
>laminar flow within the tubes, the surface heat transfer coefficient goes to
>hell, with a big drop off in cooling efficiency.

You totally lost me.  You *HAVE* to have so much CFM to make so much HP.  You
want that at the lowest PD possible with the highest delta T.  What you will
find is that high internal friction IC's (like audis internal turbulator
type) do really well in parralel, if you are going after the best of 3

>You have your low pressure
>drop IC, but with poor cooling capability.  Not an optimum solution when the
>goal is maximum heat removal.  The same thing holds for the cold side of the
>IC, thus I agree with you, that frontal area, fronting directly into ram
>air, is all important, but for this additional reason.

When you run two short IC's in parrallel, you have effectively slowed down
the velocity in both, which means your pressure loss is less, AND you have
increased cooling capacity and increased cfm.  All win/wins.  Again, this
isn't anything new, in theory or practice Bernie.  In terms of the audi IC's,
I've put davtron guages on quite a few, and the theory is no different in the
audis IC's.  What also appears to work (btmt) is two long high flow ICs, run
double pass.  The guy that did this, did it by accident, I asked.

>As for trade offs, they are personal, mine being different than yours.
>Cost always is a high priority with me.  I enjoy doing things well on the

You can't go wrong messing with Audi IC's, btdt.  That 944TS IC is darn good
as well (got that).  Parrallel two audi IC's isn't anything new, nor is it
just a cost thing.  B4B it''s just hard to beat the audis IC designs period.


Scott J

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