R it's a good question and I'm glad you brought it up. Also, thanks for posting the reply.
The intent of the Classic Category is to run the old mechanical stuff and not modern computers that manage everything on the motor in real time. A good example would be the O2 sensor. The sensor sends data to the ECU in milliseconds, along with a myriad of other data, and the ECU tweaks the EFI injectors to provide a precise AFR. Any aftermarket system like that would be illegal. Classic Category wants you changing the Hilborn pill after the run and not an ECU controlling injectors during the run. Nevertheless, you can still legally use an O2 sensor to record data to be used for analysis after a run. Also, a stock ECU system before 1981 is legal.
However, in later years aftermarket ignition system have become sophisticated and are managing themselves in real time without driver input. Good examples are the MSD series 7 and 8 systems. They provide, automatic boost retard, various ignition curves, and other automatic triggers all input by a driver before the engine is started. The key here is that once the motor is started the unit is standalone and there is no other sensor feeding information to the unit that will change its behavior.
Historical Reference up to 2010:
2.Q Computer: Vehicles may be equipped with a computer which affects engine operations ONLY, e.g., Timed fuel injection, etc., except in Vintage Engine classes, see section 2.A.1.
This rule has always been excluded or barred from the Classic Category.
Historical Reference 2011 to date:
2.Q Computer: Vehicles may be equipped with a computer which affects engine operations ONLY, except in Vintage Engine classes, see section 2.A.1.
The wording Timed fuel injection has been deleted in all rule books since 2011. I think it has added confusion to the Classic Category because the original intent still stands. No computer management of engine parameters from sensor feedback.
In the case of the MSD unit or a Boost control device, these are individual modules that are responding to inputs, or decisions, made by the driver before engine start. In some cases the driver may be able to change them during a run. But it is being managed by the driver and not a computer.
My apologies for the log post. I tried the best I could. Your comments are valued.