Re: Intercoolers and Digital boost control

["Graydon D. Stuckey" <graydon@apollo.kettering.edu>]

On Fri, 26 Jun 1998, Janet Scruggs wrote:

> where Roland Mayer relates: "Fundamentally, most car air conditioning
> systems have excess cooling capacity.  In the case of the A8, the system

Definitely not.  Many old cars had excess capacity, but not anymore.  
Even the LS400 can be caught undercapacity in really hot conditions.

> can drop the temperature to 5deg C but, in practice, goes down to only
> 15deg, so there is plenty of headroom to work with.  Once I knew this, I

Most A/C systems drop the outlet temperature to about 35 - 40 deg F (just 
above freezing) to prevent ice buildup in the evaporator core.  If we 
could be guaranteed that the air would be dry, we could drop the temp 
even lower.

> realised [sic] that it could be put to good use as an intercooling medium
> for the charge cooled air where the air conditioning pipes carry the
> coolant through a small intercooler sitting in the V of the engine."

I'd be surprised if it was very efficient.

> for such use.  I assume the idea is to use the flow from the low pressure
> return side, which is usually cooler than ambient air.  Given that the

Yes, the high pressure side of the system goes through an expansion 
valve, after which it can absorb heat.  This is where the evaporator 
goes.  After the evap, there is sometimes still some capacity to absorb 
heat, so you'd want to put your intercooler evap there.

To give you an ide of the capability of a state-of-the-art modern vehicle 
A/C system, the new Seville flows about 320 cfm of air through its air 
control module with outlet temperatures about 35 - 40 degrees with an 
ambient of 75 - 80.  A smoother flowing system would probably flow 400cfm 
fairly easily.   I suspect 
that the twin turbo 4.2 V8 probably flows about twice that airflow.  
Also, the desired temp drop in an intercooling system would be much 
greater - probably 200 250 degF out of the turbo, and we want that down 
to ambient (or lower).  That's about a 150 deg drop.   I don't think the 
A/C system is going to produce that kind of temp drop at those flows.

> 18 psi.  And, yes, I've grounded the fuel shut off relay.  A word here to
> those struck with horror at the idea of defeating a factory initiated

Horrors, Aaaaaaahhh!!

> surroundings will no doubt notice the difference between normal
> acceleration and if our car should suddenly accelerate like an F-18 on a
> catapult shot.  If it does, then something in the system is behaving
> abnormally,

"Abnormally?"  I'd say, my new turbo was working well.  :-)  F-18 
acceleration is exactly what I'm looking for BTW.

> increased performance then take responsibility for same.  If your engine

Oh yeah, that responsibility thing.  Oh well.  It was a nice dream while 
it lasted.

> or intermittent problems, but machinery in never capricious or moody. 
> (Yeah, yeah, I know.)

Apparently you haven't owned an Audi for very long.  :-)

> Except for the installation instructions, which were written by someone far
> too familiar with the unit's operation

and unfamiliar with the English language (or even American for that 
matter...)  :-)

Later,
Graydon D. Stuckey

"There's alot more to Jazz than just wrong notes"