The math behind a 2s is fairly simple. The 4s is a bit more complex because to do a 30 amp discharge with 1ohm resistors requires a combination seroes parallel circuit. OHMS law states voltage= amps X resistance. Or to rewrite it to figure out how much current you are drawing amps = voltage / resistance. The voltage somewhat varies if you are not using a icharger regenerative discharging so just use the peak voltage of the battery for the safest route. Resistance can be calculated a couple different ways the easiest way for me to explain it is by using resistors of equal value. Using this formula (1 / n ) X (value of resistor) where n is the number of resistors you put in parallel so if you use 4 resistors in parallel you get (1 / 4 ) X 1 = .25 OHMS and putting that into ohms law you would get 8.4/.25 = 33.6 amps. Watts law is power= amps X voltage you get 8.4 X 33.6 = 282 watts which is quite high. That power would be distributed across 4 resistors equally so each resistor dissipates 70.5 watts which is why I recommend 100 watt resistors for safety. The fans and the heat sinks are to help control that much heat.