John,
I've been doing Industrial controls since 92 or 93. Mostly the hardware design, but I have been known to do programming also. The last 7 years have been designing build equipment for seat manufacturing and calibration/verification test equipment for air bag deployment. This is sort of a lie as I have been working as an engineer for the last three years at a float glass plant, but as a side job I contract myself out to a company that does the seat equipment.
I have thought about using a PLC in a car for years, but have never had the reason to do so. I've never put down the amount of N2O that you guys are using and I don't race competitively, so I didn't have a need. I did hear that Monster trucks were using a PLC to shift the transmission.
Something to look at. I’m not an AB sales man here, but use their equipment. The Micrologix 1400 controller (1766-L32BXBA) would be a good candidate. It uses 24VDC for the power input. It has (6) 100K High Speed inputs, (4) voltage analog inputs, and (2) voltage analog outputs. I believe that it can be expanded with I/O modules.
The down side to this is that it’s AB and you have to purchase their software, but if you have RSLogix 500 and RSLinx available it might be a good choice. Again there is the problem of a 24VDC system for the controller. 2 batteries can take care of that problem. Most guys seem to run two anyway. You can run them in series to get 24 VDC for the PLC and use a heavy duty voltage divider for the rest of the car. The starter might be a problem as I do not believe the starter motor could take the 24VDC, but a heavy duty Zener Diode and shunt the excess voltage (above 14volts) to ground. OK there you have it a very expensive and complex way to put a PLC into you car.
It looks like the Carbon fiber in Scotts show set up is covering just the power source. Probably a 120/24VDC power supply. I'm betting that the HMI has the PLC built in.
John