I was looking into 2 speed fan controls using electronic controllers, resistors or swapping motors. What I ended up doing is to simply re-wire the stock system and replace one of the relays with a DPDT relay. This allowed me to wire the motors to operate together, but in series when the first relay kicks in. The motors operate at about 1/2 speed. When the second relay kicks in both fans operate on full speed. Simple.

I choose a fan switch for the head which is set just above the thermostat temp so the fans come on low when the engine comes up to temp. The computer (and an adjustable fan switch in parallel) then kicks the fans into high speed when the temp starts to climb.

I used a fan/motor/shroud setup from the 98-02 Camaros which uses the same fans and motors as stock, it simply adds a shroud. The trick here is to mount the assembly upside down to gain clearance at the steering gear box. Of course some trimming of the shroud and top radiator support is necessary but not a major deal. If a car came with the single fan this would be an easy way to add dual fans.

I am set to use the stock radiator with my 421 build and believe it will be sufficient. If not a larger radiator can be added and still utilize the fans and controls.

How soes his all work? Well I don't know yet. AFR has had my heads on order for about a month and will hopefully be ready by the first of June. Then the motor will have to be completed and installed so we may be looking at July here. A perfect time to "max test" a cooling system on a 500+ HP motor lol!