Re: a2a OR w2a
No offense taken. I love to work out the brain cells! I am going to suggest you do some research. There are several books you can read and or information on several web sites.
Using my own personal experience, and that of my ol' boss, Gareth Howell (British Touring car guy). We can see it consistently on the engine dyno. Gareth likes to use the customers complete intake, exhaust and intercooling set up when tuning. The dyno cell also has its own chargecooling tank. We see more consistent temps as well as lower IAT's. Hands down water/air is the way to go. Water to air plus chemical intercooling... now we are talking! Now that I have touched on actual real world experience, I am going to break out some technical info I found with a quick search.
Water has a much higher specific heat value than air. The 'specific heat value' figure shows how much energy a substance can absorb for each degree temp it rises by. A substance good at absorbing energy has a high specific heat value, while one that gets hot quickly has a low specific heat. Something with a high specific heat value can obviously absorb (and then later get rid of) lots of energy - good for cooling down the air. Air has a specific heat value of 1.01 (at a constant pressure), while the figure for water is 4.18. In other words, for each increase in temp by one degree, the same mass of water can absorb some four times more energy than air. Or, there can be vastly less flow of water than air to get the same job done. Incidentally, note that pure water is best - its specific heat value is actually degraded by 6 per cent when 23 per cent anti-freeze is added! Other commonly-available fluids don't even come close to water's specific heat value.
The high specific heat value of water has a real advantage in its heat sinking affect. An air/water heat exchanger designed so that it has a reasonable volume of water within it can absorb a great deal of heat during a boost spike. Even before the water pump has a chance to transfer in cool water, the heat exchanger has absorbed considerable heat from the intake airstream. It's this characteristic that makes a water/air intercooling system as efficient in normal urban driving with the pump stopped as it is with it running! To explain, the water in the heat exchanger absorbs the heat from the boosted air, feeding it back into the airstream once the car is off boost and the intake air is cooler. I am not suggesting that you don't worry about fitting a water pump, but it is a reminder that in normal driving the intercooler works in a quite different way to how it needs to perform during sustained full throttle. However, the downside of this is once the water in the system has got hot (for example, after you've been driving and then parked for a while), it takes some time for the water to cool down once you again drive off.
Hope this helps,
Steven
