What is the best air intake for a Mazda RX-7 FD?

Difficulty: Easy to Moderate

Upgrading the intake on the FD RX-7 wakes up the top-end power nicely and removes the cumbersome factory airbox ⁷. Because turbocharged rotaries generate significant under-hood heat, the "best" intake depends heavily on keeping hot engine bay air away from the turbos.

Here are the top options based on performance, design, and budget:

Enclosed / Cold Air Intakes (Top Recommendations)

These are generally considered the best options because they isolate the intake from engine heat and draw cooler air from the front of the car.

• AutoExe Ram Air Intake System: This is highly recommended as it pulls fresh outside air and completely blocks hot radiator and engine bay air. Because it is an enclosed box, it can amplify the sound of the stock blow-off valve and turbo transition. If you prefer a quieter ride, you can spray the inside of the box with an automotive sound/heat insulator (like LizardSkin) to dampen the noise and further reduce heat transfer ⁷.
• M2 Airbox (or CX Racing Replica): The M2 is a highly sought-after carbon fiber box that draws cold air directly from the bumper inlet. Original M2 boxes are rare and expensive, but CX Racing manufactures a viable replica. Keep in mind that the M2 box will not fit with a GReddy V-mount intercooler without heavily modifying the box ⁷.

Open Element / Pod Filters

These kits look great and free up engine bay space, but you must fabricate a custom heat shield and fresh air ducting; otherwise, they will suck in extremely hot air, reducing your intercooler's efficiency.

• A'Pexi Power Intake & HKS Super Power Flow: Both are dual-cone setups that replace the factory airbox. The HKS is known for its excellent design, but it requires filter replacements roughly every 6,000 km. The A'Pexi replacement filters are non-washable and run over $80 each ⁷.
• Pettit Racing: This system uses dual K&N filters but includes an aluminum heat shield designed to block engine heat and coerce cooler air from the front of the vehicle ⁷.

The Stealth / Budget Option

• Modified Stock Airbox ("Cheap Bastard" Mod): If you are on a budget or need to pass a visual emissions inspection, you can modify the factory airbox. By capping the hole in the top of the stock duct and dropping in a high-flow K&N panel filter, you can improve the air supply to both the turbos and the intercooler while keeping a completely stock appearance ⁷.

Verdict: If your budget allows, the AutoExe or M2/CX Racing enclosures are the most efficient off-the-shelf options for keeping intake air temperatures down. If you run open-element pod filters like HKS or A'Pexi, ensure you build a heat shield and run a cold air duct to get the most out of them.