Guys, take a step back and look at this for a second. Parts of what most people are saying are right, and parts of what most people are saying is wrong. PV=nRT. Yes, that is true. ANd an increase in pressure will cause an increase in temperature, and vice versa. It is also true that a DECREASE in temperature will cause a decrease in pressure.
All of that is perfectly fine and repeatable - in an isolated system.
Guess what, fellas, we don't have an isolated system. THe fact that air is constantly moving in and out of the system means that a pressure drop will be caused by anything impeding flow. And the fact that the intercooler does not seal the two sides from each other means that they would be at the same pressure if there were no airflow. YOu put the two together, and you'll find out that the intercooler creates a pressure drop in the system by resisting flow, not by cooling the air charge. It is equivalent to a resistor in an electrical circuit. YOu don't like that example, it is like a nozzle on a garden hose.
Did I just agree with Mike? Wow.
But, I do take issue with the statement "pressure drop is not caused by a good intercooler, it is caused by a (crappy) one." THere are two critical factors when it comes to intercooler design - resistance to flow, and efficiency. Often, they work against each other (internal fins, like on an NPR, are a restriction, but they help dissipate heat better than one like a Volvo which is open).
NOw, another thing - volume kind of changes, but not really. If you have the same size pipes on the inlet and outlet, a cross section of each gives you the same volume. Yet one side has cold air, and the other has hot air. THey may very well be at the same pressure. The difference, as someone pointed out, is density. An intercooler will increase the density of the air charge. The only volume change occurs when you change shapes of things. An intercooler may be absolutely huge, which will increase the volume. What this does is slow down the air as it moves through the intercooler, which gives it more time to do its work. THIs helps things bcause you'll have a higher mass of air flowing over teh intercooler, meaning more abililty to move the heat out of the intercooler.
Now, the fact that we are flowing air in a non-isolated system is why mass flow is what is so important, not pressure. You can't compare an isolated system like a tire to ours, because they are totally different animals. If it were as simple as pressure, there would be no benefit to using a larger turbo. I mean, a T3 will boost our engines well over 20PSI. Why bother with a hybrid? Because it increases the mass of air that can be flowed because it is cooler, and therefore more dense. Then you get into the whole volume flow thing in the engine when talking about how much air you can actually flow into the engine, but that is another argument for another day.
BUt, to get back to the original question, my take on it is that both would be stellar. However, liquid (water, water/alky, alky, propane - whatever) injection has a few drawbacks in that (to my knowledge) it can't be duty cycled. So, it really only hits its peak operating condition at a point. Meaning, you can spray X/time flow of water in the system. AT 3000 RPM and 20 PSI, the amount of air cooled by teh water is a lot higher than the air cooled by the water at 6000 RPM. If you are saturating teh air at 5000 RPM, then at 6000 RPM, you need more, and 3000 RPM, you are not evaporating it all. Further complicating the situation is the variation in boost pressure. At 15PSI, a given system will inject more water than at 20 PSI (less resistance to water flow). If you have the ability to raise the water's pressure (as a FPR does) with boost level, then that isn't an issue. But, that makes it really messy.
But, water injection has other benefits, like raising your effective compression ratio, and less need for fuel enrichment.
The good thing about an intercooler is that you don't have to worry about oversaturating the air. If it cools it off before it is all of the way through the intercooler, there are no bad side affects. Bottom line is that the intercooler is just a lot simpler, and offers most of the same benefits.
IMHO....if I were setting up a system, I would only consider water injection AFTER I had an intercooler in place. I'd shoot for the best intercooler I could find, and if there is still potential for benefit for water injection, then I'd pursue it.
Hey, waitaminute, that IS what I'm doing!
