First Event In A Supercharged Miata: Shenandoah Circuit

Published: July 22, 2015

I picked up a Kraftwerks Rotrex supercharged Miata on Thursday and took it to Shenandoah Circuit event sanctioned by WDCR SCCA on Saturday and Sunday. The result was a lot of grins and some disappointment.

The Car

The car was a reasonably well put together street Miata with a supercharger. Some highlights:

  • Flyin' Miata springs and shocks package
  • Stock brakes with mystery street pads
  • Kraftwerks supercharger with ~9 psi peak boost
  • Stock cooling system
  • Air conditioning

Street Test Drive

I test drove the car before buying and was impressed with the power level. In second gear the acceleration was basically insane, at least for a Miata. Third gear was winding out quickly and with it the legal limits were rapidly approached.

I elected to purchase the car and see what it can do on the track.

Track Manners

The car is mountains of fun at the track. It has enough power to pass just about everything sensibly once a point-by is received. Shenandoah generally brings out low power car clientele, hence I have not yet had opportunity to battle well driven Porsches and Corvettes (with one exception).

The extra power transforms Miata into a medium power car at the very least. It still qualifies as a high grip car, thanks to 245/40-15 Maxxis RC-1 tires I thoughtfully packed, but it most certainly does not run naturally aspirated Miata lines without modification.

This supercharged Miata, only having street springs and shocks, not to mention street alignmnet, did not handle as good as my naturally aspirated track Miata. I intend to move the track suspension to the supercharged Miata eventually, and at that point I expect the supercharged Miata to be as fast or faster than the naturally aspirated Miata anywhere on any track.

Cooling

One lesson that I learned was that the stock cooling system is completely worthless at the track.

I did not expect the car to last 30 minutes at a time, but I certainly expected it to last 15. Unfortunately the weekend was extremely hot - peak ambient temperatures above 90 degrees F - and except for a single session on Saturday morning in rain the car ran for one lap before the temperature gauge was pegged hot.

To combat the overheating we removed the thermostat on Saturday afternoon and then air conditioning condenser on Saturday evening but this barely changed the cooling situation.

A race radiator and a coolant reroute are a must for tracking the car. So are warning lights (first time the car overheated I noticed it because it died...).

Brakes

One of my concerns was brakes not lasting a full session before fading. The brakes has not caused a problem on track because the coolant had much lower usable life than brake pad material. That said, even in the few laps I did run I felt what I would describe as pad fade. Forced induction Miatas need aftermarket brakes.

Traffic

With an estimated 170-200 whp and 245 width R compounds the supercharged Miata laid waste to the advanced run group. Less than properly advanced drives in high power cars do not stand a chance.

My most pleasing achievement was passing an instructor friend in C5 Z06 Corvette. I had to work for it, which was expected, but being able to pass instructors in high power cars makes the aggravation of dealing with forced induction worthwhile. I figure a well driven supercharged Miata can be in the top 5-10% of the instructor group at a typical track day.

Conclusion

The car is plenty of fun and with proper cooling, brakes, better suspension and - maybe - even some aero it should be a beast!