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Intercoolers and Digital boost control
I've been on the road for the last ten days and am trying to catch up on
digest traffic so if this has been mentioned then excuse the redundancy.
The other day in Mobile I picked up a March/April '98 copy of "Audi Driver"
which contained an article on a twin-turbo A8 project by the Audi tuner,
MTM. Nice car! Twenty inch wheels are startling at first but visually
shrink the A8s size. Anyway... there was no room for an intercooler so
they came upon an interesting solution. Quoting a section on page 20,
where Roland Mayer relates: "Fundamentally, most car air conditioning
systems have excess cooling capacity. In the case of the A8, the system
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
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."
Corky Bell mentions both the added efficiency and added complexity of
liquid-to-air intercoolers, although usually using their own small water
cooled systems. I would not have thought of using the A/C working fluid
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
liquid-to-air cooler is significantly smaller than the air-to-air cooler,
perhaps it could be placed very nearly between the compressor output and
the throttle body. The remainder of the space where the old cooler went I
would use for an enlarged oil cooler. Any ideas?
The only high performance use I've thus far found for my A/C was defogging
my windscreen during the Sunday rains at Thunderhill last January.
The other topic is the use of digital non-ECU boost control. I've been
using an HKS EVC III to control boost in my '87 5kCSq for about a year now
and wish to report that it has no bad habits and is willing to learn. The
previous statement is with malice of forethought as the unit has a fuzzy
logic circuit that "learns" the boost characteristics of the engine/turbo
combination and adjusts the rate at which the wastegate opens such that the
"cracking" point is held off as long as possible. This results in a _much_
improved part throttle response.
I should explain that the unit contains a pressure sensor that is accurate
to 3.0 bar (absolute) and also has a great huge wastegate frequency valve
that replaces the OEM one. (Graydon Stuckey described the HKS frequency
valve as looking like a body part from The Terminator... and he is
correct.) The HKS unit completely takes over the boost control function
from the ECU.
This unit is adjustable such that two boost levels are available and
selectable by switches. I have them set at 1.8 and 2.2 bar or about 14 and
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
'safety' device. These cars are carefully designed by engineers and
lawyers to be successfully driven by idiots. And these idiots may
encounter a vast array of conditions and failures which may escape their
notice. Those of us who are more in tune with the physics of our
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, _take appropriate action_! If you are modifying your car for
increased performance then take responsibility for same. If your engine
blows to bits as you reach Mach 1 between stop lights then don't
complain... you knew something was different. Machinery may have complex
or intermittent problems, but machinery in never capricious or moody.
(Yeah, yeah, I know.) Pay attention... and enjoy the improvements to your
I find that running at these boost levels can reveal new challenges. I
find that 2.2 bar at WOT I have a miss/power loss that I can't explain.
Scott Mockry fixed my WOT switch at Thunderhill but I've not found the rest
of the problem. Suspecting that the knock sensor is chopping the ignition,
this afternoon I added two gallons of 115 octane racing gas to the tank and
was greeted with a nice strong pull in ranges where only stuttering had
previously occurred. Looks as if I now must address all potential causes
Except for the installation instructions, which were written by someone far
too familiar with the unit's operation, I am very pleased with my HKS boost
Regards, Gross Scruggs