Why is engine heat coming into the cabin of my Mazda RX-7 FD?

In the Mazda RX-7 FD, cabin heat usually radiates from the exhaust and transmission directly through the thin metal of the firewall, floorboards, and transmission tunnel. This is exceptionally noticeable if the car has a stripped interior or removed sound deadening.

To resolve this, it is highly recommended to install heat shielding underneath the car rather than trying to insulate the interior. Shielding the undercarriage reflects the exhaust and drivetrain heat before it can absorb into the metal of the cabin ¹.

Here is how you can address the heat transfer:

• Underbody Shielding: Apply a thermal barrier directly to the firewall and transmission tunnel from underneath the vehicle. Products like DEI floor and tunnel shield or Heatshield Products HP Light Floor Shield are effective for this ¹. Before installing any adhesive barriers, you must thoroughly clean and degrease the surface to ensure it sticks properly ¹.
• Transmission Heat Shields: Add physical heat shields between the exhaust and the transmission to cut down on the localized radiant heat ¹.
• DIY Floor Buffer: If you are primarily feeling the heat through your feet, you can build a DIY buffer out of wood stock to space your feet slightly off the bare floorboards. Even a very small air gap makes a massive difference in the heat transferred directly to your feet ¹.

Difficulty: Easy. The thermal shielding materials are generally easy to work with, though the job will require safely raising and supporting the car to access the transmission tunnel, as well as spending the time to thoroughly degrease the undercarriage.