Bullitt347, I reeeeally don't want to offend you, man. If you start to feel angry about my counterpoints, I will stop... Just let me know.
No problem, I enjoy a good debate/discussion as well as the next guy.
Efficiency is not measured in this way. You're referring to specific heat... not efficiency. And, you're right, the difference in specific heat of water vs. air is about 4:1.
http://www.iun.edu/~cpanhd/C101webnotes/matter-and-energy/specificheat.html
Ice or no ice, there is no way to reduce the air charge to less than ambient without bringing the water to below ambient AND there is no way to do that using the atmosphere to cool the water. Whether you use ice, colder water, or frozen carrots to cool the liquid heat exchanger doesn't matter. You can't do it continuously for long periods of time while driving on the street. You're limited to short bursts.
I have watched the data-logs real time on an air/water supercharged car have 58* air inlet temp and seen outside ambient temp be 65* while cruising...not in boost...with no ice in the tank.
Packaging is the largest reason for going with a water to air heat exchanger. Another acceptable reason is short bursts of cooling before the water is heat soaked.
This is why I have an 8 gal water tank in the trunk............huge heat sink!
Careful. Without constantly adding some other cold medium, all intercoolers must eventually use the surrounding atmosphere, and are thus subject to the same concerns.
"efficiency ratio" is not the correct term, as laid out above. That's not true... At least the "4 times larger" part. Specific heat ratio does not necessitate that you need 4 times as much air in the intercooler, or a system 4 times as large.