cross flow vs. up and down-aluminum radiators

fyi, they have a new technology for downflow rads. its called double pass and triple pass which means it goes up and down 2 or 3 times before it exits. i tend to disagree that aluminum is more efficient than copper/brass. at the same temp(180) copper/brass has a thermal transfer rate 2 times that of aluminum. for whats known as "steady state heat transfer" which is what a radiator does, copper will always yield a lower temperature. remember, copper is more dense than aluminum, so it will retain more heat for a bit longer, and in a sense take a bit longer to cool down. in my radiator, i moved the tubes from 1/2" on center to 3/8" on center, made it a 3 row and used a core that had the tubes "dimpled". this slowed the water flow down a bit in the radiator. the longer the water is in the rad, the more heat will be pulled(dissipated). a radiator is only as good as the air moving thru it, so a good fan and shroud is a good thing. aluminum is lighter for racing. remember to use a RADCAP!!!! this will stop the electroysis of all the dissimilar metals you are connecting by the water flow(copper, cast iron, aluminum, chrome, steel, etc.) see it at www.radcapproducts.com