Track Day MX-5: the Supercharged Bathtub

1 minute read

miata

Over the years I’ve built cars for various purposes, and in doing so I’ve realized a few things…

Building cars for show is not something I’ll repeat.
Usable power is more fun than a number on a dyno chart.

For me, the intrigue of driving control and finesse is found in road racing (and perhaps rally). Lightweight nimble cars on technical circuits provide the most demanding arena for my personal growth as a driver. Because of this I decided to build a track car.

I chose the miata for its lightweight chassis and inexpensive aftermarket options. A decent way into building the car, I realized my size (6’ 3”) prohibited me from competing in racing organizations such as the SCCA along with a few other sanctioning bodies around the area that used the following rule…

“a drivers helmet must be 2” below a broomstick extending from the windshield to the rollbar/roll cage”

I tried mounting a kirkey racing seat shell directly to the floor pan but I was still too tall. I guess I wasn’t cut out to race a miata in officially sanctioned leagues. I did however proceed to turn the little bathtub into a phenomenal track day toy. I may not be allowed to compete in any sanctioned racing, but it rips up a small track better than any other car for the same money. Besides, I turned to shifter karts for some much more intense racing anyhow.

Maintenance

Hardtop

Rollbar

Suspension

Supercharger

Sensors, Gauges and Engine Management

Cooling

Intercooler and Radiator and custom aluminum cold air box.

Clutch

Custom Dual Throttle Bodies

The intercooler and associated piping would introduce air volume that acts a sort of slack in the throttle response. To compensate, my dad fabricated a set of custom bracketry to handle a second throttle body. By creating a staggered dual throttle body setup with slightly different cams, the throttle response is increased while the wide open flow rate remains the same.