UrQ Intercooler Solutions

John Cody Forbes cody at 5000tq.com
Thu Feb 1 00:22:05 EST 2007

E. Roy Wendell IV wrote:
> Contrary to popular believe, intercoolers act much more like
> a heat sink than a heat exchanger. They absorb temperature spikes
> during boost and then shed much of the heat back into the intake air
> when off boost.

Exactly true. A larger pysical size and thick wall ala 951 intercooler does 
the street job great. I also agree that a fan most likely won't help much, 
other then to help remove extra heat when sitting at a traffic light and to 
prevent heat soak (which isn't a major issue with your setup anyway).

> As far as I'm concerned air-to-water is the solution for street and
> drag intercoolers.

I tend to have different opinions here. Water-Air systems do work well for 
short burst use, but there are even better ways to get the job done.

 For stree use a water-air system is a huge mass of schtuff that must be 
figured out, plumbed, and designed. Think of it, you have to route 2 
somewhat large hoses from your trunk to the engine bay all the while keeping 
them away from soucres of heat such as exhaust, road, engine, etc. Then you 
need a tank, a pump, a bit of wiring, maybe a thermoswitch or two in a well 
implimented system. Then you need a second water-air exchanger to take the 
heat out of the water, unless you just use the waters volume like a heat 
sink. Then to ever expect optimal results you need to add ice, which will 
(hopefully) bring your intercooler temps down into the high 30*F area. Of 
course they do have the advantage of the following setups of not needing to 
be refilled.

For drag use a water-air is better then it is for street because basically 
you build an intercooler in a box, then fill the box with an icy water mix 
and you are done. By the time the ice melts you are already drinking beer 
and (hopefully) holding your trophy.

I prefer an air-air IC with cooling assistance for street use. Water, CO2 
and N2O are both good for this purpose. Water spraying on an air-air 
intercooler, if done properly, can be exceptionally effective. Champion 
Racing employed water spray on both thier S4s and RS6s, I personally have 
inspected thier very well done systems. Basically you need a tank, some 
water, one very small hose, and a nozzle or two to spray the most fine mist 
you can possibly find, plus a pump and a way to turn it on. The evaporative 
cooling achieved here works wonders. Then comes the compressed gases. Both 
CO2 and N2O (yes, nitrous oxide) work really really well here. For these 
systems you need a small tank, one very small hose, one solenoid, and one 
nozzle, pls something to activate the solenoid. I'm not sure of the exact 
number on CO2, but N2O exits the nozzle at -127*F. Thats friggin cold. Of 
course the N2O option leaves the obvious choice of also injecting some 
directly into your intake air stream ;-). Even a teeny ammount injected into 
your intake air will be a huge increase, because even though the power boost 
from the N2O itself won't be much you will be cooling your intake air 
directly with a gas that is well below freezing.

Another option of course is installing a better intercooler ahead of the 
radiator. I'm not too up on who makes what, but I built and installed a 3" 
thick, 30" wide, 12" tall intercooler in the front of an A4 before, 
retaining A/C and all. 

Bottom line - for your A4 I wouldn't worry too much about any of these 
options, unless you are turning street racer on us ;-). If you enjoy the 
occiasional stoplight to stoplight power burst then maybe a simple water 
spray, or maybe even a compressed gas spray is right for you. If you want to 
have a better setup for track days then look for a better intercooler. 
Water-air systems are too involved for casual street use.

-Cody Forbes
'86 5k noT noQ
'86 5k noT noQ - Parting Out
'87 5ktq
'87 5ktq - Fast. Really Fast. 

More information about the quattro mailing list