Two hours into my endurance race stint, my foot was on fire, literally. By the time I stepped out of the Total-D Miata, I had a second-degree burn. Welcome to the world of Miata hot foot.
What is Miata Hot Foot?
Early Miata’s have a driver’s side footwell heat issue termed ‘Miata hot foot.’ The headers and exhaust run between the transmission tunnel and the driver’s foot box, trapping heat that then soaks into the firewall and transmission tunnel.
This excess heat is a nussiance in a street car. Giving the driver a bit of discomfort. But in racing applications, this trapped heat becomes dangerous, even causing injury.
Want to See an Extreme Example of Miata Hot Foot?
During my two hour stint in the Total-D Miata, I noticed the right side of my right foot was getting hot. Then I noticed it was getting really hot. And then, well I knew my foot had suffered a burn from the heat.
But this was after I had placed the car in 1st place and was consistently banking the team time. So instead of pitting early, I moved my right foot away from the heat source by adjusting my inputs as much as possible. Minimizing the time my right foot was near the transmission tunnel. In the end I was able to finish the stint, lap the p2 car and walk out of the car with a second degree burn on the right side of my right foot.
Here’s what that looks like.
Not too bad I guess but the healing cycle of a deep blister can get painful and a little gross. Luckily, I will keep those images to myself.
What Causes Miata Hot Foot?
Miata hot foot occurs in both the NA and NB Miata’s where the headers and exhaust run on the drivers side. Because of this configuration, the sheet metal around the right foot and the transmission tunnel gets particularly hot. The absorbed heat from the exhaust radiates heat into the footwell.
The result in a racecar? A painfully hot foot, or in my case, after a two-hour race stint, a burned one. And with no interior or shielding, the sheet metal becomes to hot to even touch.
Solutions for Miata Hot Foot
Solving Miata hot foot is straight forward. We need to insulate the exhaust and then reflect as much heat as possible from the sheet metal. This will be done with a combination of heat wrap and heat reflective film. The heat wrap with cover the headers and exhaust up to mid transmission tunnel. The heat reflecting film will be placed under the car in the areas the exhaust runs closest to the footwell. (The firewall/transmission tunnel area.)
For the exhaust wrap I will use this kit from Sunplus on Amazon. I have used their heat wrap before and they work great and include the metal ties.
For the Miata firewall and transmission tunnel insulation I am trying this adhesive backed heat reflective sheet from BBTO. I will report back on effectiveness but the price is too good to not try out. The established brands sell heat reflective sheets at $33/sf where the BBTO offering is less than $2/sf.
Exhaust Wrap vs Ceramic Coating
I am using exhaust wrap but there are also coatings that can be applied to the exhaust to help with heat control. Namely, ceramic coating. And i found these two youtube videos very helpful in determining which route to go. They both demonstrate that the wraps work and that they outperform ceramic coatings when looking just at heat reduction.
Other benefits of the wrap is its DIY and way less expensive than coatings.
What If That’s Not Enough? Active Cooling Options
The wrap and heat reflecting should 100 percent solve the Miata hot foot issue in the racecar. But what if it doesn’t? The next enduro in the car is coming up and I have a third solution if these passive systems aren’t enough.
The third solution is to direct airflow via a small fan downward into the footwell. This will push cooler air over the radiant heat area. Effectively cooling it off on the drivers side. For this purpose a 12v boat style blower would be compact enough to mount under the dash and can be plumbed with a naca duct to move air around the footwell.
Conclusion
I had slightly burned my foot in the past driving my own Spec Miata but had never suffered the damage I did during the 2 hour stint in the Total-D Miata. Needless to say the passive solutions will be in place before the next endurance race and I will be equipped with the parts to install the active solution if there is even a hint of a chance at another burn.
