I made my own CAI. See here:
http://ecomodder.com/forum/showthrea...ctd-22770.html
We got into some of the efficiency details too. The effect is fairly small, but basically a diesel like colder air for better efficiency up until the point the combustion gets significantly retarded due to the longer ignition delay. i, personally wouldn't get too concerned until ambient temps get at least below 20 deg F. We recently had temperature dip below zero here, so I temporarily plugged mine. I was getting some white smoke of start ups without my grid heater.