Due to nerve damage in my left leg resulting from aggressive radiation to combat cancer in my lymphatic system, I progressively lost feeling and then control of my lower left leg. Due to this result, I stopped racing cold turkey. The cars went in storage or were sold off. During this progressive deterioration of feeling in my leg, I managed to develop a left hand actuated clutch for my Porsche Boxster S and 996 Carrera 4 with LS3 conversion. While this worked for basic street driving, more hands were needed and much quicker response was needed to drive a race car.
I first developed the prototype of my air clutch on a 1964 MG Midget with 1380cc (“big bore”) engine and 5 speed Datsun gearbox. I still have this car.
My next step was to start vintage racing. Although I had bought a roller 1959 Austin Healey Sprite “Bugeye” to prep for racing with CVAR – Corinthians Vintage Auto Racing, I got impatient and wanted to go to novice school quickly. I bought an old 1969 SCCA FP car from another racer and got to work converting it. I attended the school and on the last day managed to come in contact with a spinning car and knock the front right fender and suspension off the car. How embarrassing, but the first “race weekend” with the new air clutch was a success!
For the rest of my novice season, I raced with CVAR group 7 (mid bore) as my car was too heavily prepared (coilovers, four wheel disks and flares) to run with the standard FP cars in group 2. The club where aware that my goal was to have the group 2 legal “Bugeye” ready to race the following year.
I have now been racing with CVAR for 6 years and am one of the group 2 reps. With the exception of two electric pressure switches corroding in our Gulf Coast humidity and easily changed at the track in about 2 minutes, I’ve had no issues with my design. I do keep spares for EVERYTHING used in this system in my race trailer, just as I keep spares for all the mechanical parts in my car. I would not travel to an out of town race without a spare transmission and engine. This is how I roll.
My shifts are fractionally slower than standard cars with straight cut gears and standard synchros, but I still managed to win the VSCDA Sprite Midget challenge for my class this year (2023), the CVAR FP class, and also podiumed all races with the SVRA at COTA in November 2025. My best year yet! If CVAR would allow it, I would use a dog box and only use the clutch for taking off from a standstill, but we must use a synchronized gearset. The dogbox would be much faster shifting……………..I know because I have one in the yellow car now and use it for fun track days at MSR-Houston. The Bugeye still has a straight cut synchro box to maintain legality in CVAR events.
The air driven clutch in my cars is very basic. It supplements the standard hydraulic clutch system with no alteration to the hydraulic master, slave, disc, pressure plate, throughout bearing, plumbing or pedal assembly. If an able-bodied person wanted to drive my car, they could do so by only turning off the air compressor and removing the two air lines from the air cylinder attached to the clutch pedal.
The system consists of:
-100% duty cycle air compressor (12 volt)
-1 to 2 gallon reserve tank with manual pressure relief valve
-pressure switch (on/off for compressor)
-pressure gauge (in line of site for driver)
-solenoid panel (two solenoids, circuit breaker, relay, bleed valves, etc)
-driver actuated stage switch (grid/race)
-stage indicator led light (Blue)
-shift knob with momentary push button (Twisted Shifterz sourced)
-air cylinder for pedal (race Bugeye shown)
-dead pedal with hook to prevent “bad” legs foot from moving under clutch pedal in race situations. Not needed if the driver is missing his/her leg.
The pneumatic automation parts are sourced from Automation USA. They are awesome and ship very quickly. The compressor, tank and pressure switches are from Viair. These are the same units used by the airbag suspension builders or guys running train horns in their jacked-up trucks. The interface brackets for the air cylinder to the body must be fabricated and must be stout.
I have included a spreadsheet with a typical bill of materials as well as a basic schematic. The air ram for the pedal will need calculation/estimation in terms of diameter based on the position of the mounting fulcrum on the body and the position on the pedal. Diameter must be matched to force needed. The length is easier. I use double acting cylinders for speed, so it is forced out for clutch actuation and forced in when the button is released. Speed is important in a racing situation.
The tank mounted air compressor is activated as soon as the race car’s kill switch is powered on. I let it pressure up prior to starting the car. There is very little leak down in the system and only the initial fire up of the day takes a couple of minutes. The compressor is generally mounted in the tail section of the car to keep the noise down, but it does need some air space to keep cool on enduros.
To leave from a dead start, the driver will make sure the stage switch is in the grid position (blue light off) and only needs to hold down the momentary button on the shift knob prior to selecting first (or reverse). To set off, the driver will need to release the switch and accelerate. This takes a little practice as you are relying on the slow bleed of the cylinder on the pedal to “feather” the clutch on the way out. If you need to stop while in first, just push the button and hold it. This allows the pedal to move down quickly when the momentary switch on the shift knob is pressed and back up slowly when it is released. The speed down is really a product of the line pressure, but the slow speed back up (feather) is a product of the inline bleed valves (needle valves).
When the driver is up to speed in first gear leaving grid and ready to shift to second gear, the stage switch must be thrown to the race mode (blue dash light illuminated). This allows the pedal to move down quickly when the momentary switch on the shift knob is pressed and back up quickly when it is released. The speed down and up is really a product of the line pressure.
I am always happy to share the particulars of my medical disability with others and my solutions. Just ask.
See you all at the track. If you see me trying to climb to the top step of the podium, please give me a hand…..Hah!
Submitted by David Lee
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