We've spent a lot of time testing cooling systems on our dyno, and this is one of the spinoffs. Read our testing results
We started with a laser-cut aluminum shroud to maximize efficiency of the fans. It ensures that all the air gets pulled through the radiator - and we mounted the shroud far enough away from the radiator to make sure the whole core gets air. Some of the shrouds on the market are far too close to the rad, meaning that only about half of the core gets airflow. We also added some flaps that allow air to bypass the shroud at high speed without affecting the draw of the fans. The shroud is made with threaded inserts to make life easier and comes with spacers to ensure proper standoff from the core.
A pair of Spal fans were chosen not only for their flow, but their ability to pull air through a stack of heat exchangers such as an intercooler and A/C condenser. Most fans are rated for their flow at 0 pressure and their performance drops off rapidly as they have to work harder. Not these! They're also low-profile enough to clear most intercooler piping. The end result is a compact package that does an excellent job of cooling high-power Miatas. They're not slim-line fans and pull a fair bit of power - but that's because they have the torque to get the job done.
There are other fan/shroud combinations on the market, but none of them have the same dyno-proven ability to pull large amounts of air through your radiator - and A/C condenser and intercooler, if applicable. Do your homework and don't get fooled by cheap alternatives.
Our Stage 1 kit pulls 4540 m3/h at 0 pressure, and is low-profile enough to fit almost anything. NA6 airflow kits include extra wiring to handle the draw of the big fans.
For non-crossflow radiators only. There's a special kit for crossflow radiators.