Tube and fin FTW - more effecient but a tad more expensive.
WMI - it basically works by cooling the intake and cylinder charge temperatures.. ie, the cooler th air, the more dense, ie more OXYGEN enters th cylinder, the Methanol has a supercooling effect in the cylinder. thats how you get more HP, because the combustion is alot more effecient. The engine burns more cleanly.
best used if youre going to use an aftermarket ecu otherwise th stocker may richen it up more...