Other's may be interested in the technical aspect of making these measurements, so I'm replying to your post.
For laughs, I asked openAI (ChatGPT) this question;
"How to filter the broadband noise while measuring spark plug voltage and current in an experimental ignition system?"
I got the following response:
"When measuring the voltage and current of a spark plug in an experimental ignition system, it is common to encounter broadband noise. This noise can interfere with the accuracy of the measurements, making it difficult to analyze the ignition system's performance. Here are some techniques for filtering the broadband noise:
1) Shielding: One way to reduce broadband noise is to shield the wires and components that connect to the ignition system. Shielding involves surrounding the wires and components with a conductive material such as copper, which blocks electromagnetic interference (EMI). Shielding can be effective in reducing noise that is picked up by wires and other conductive components.
2) Filtering: Another technique for reducing broadband noise is to use filters. Filters are electrical circuits that attenuate or remove unwanted frequencies. For example, a low-pass filter can be used to remove high-frequency noise from a signal. Filters can be implemented using passive components such as resistors, capacitors, and inductors, or with active components such as operational amplifiers.
3) Grounding: Proper grounding is critical for reducing broadband noise. All components of the ignition system should be properly grounded to minimize noise induced by ground loops. Ground loops occur when different components of a circuit are grounded at different points, causing current to flow between the grounds, which can create noise. By grounding all components of the ignition system to a common point, ground loops can be eliminated, and noise can be reduced.
4) Twisted Pair Cables: Twisted pair cables can be used to reduce electromagnetic interference (EMI) and radio frequency interference (RFI). These cables are made up of two conductors that are twisted together, which creates a balanced signal. When EMI or RFI is present, the noise is picked up by both conductors equally, and the balanced signal is maintained. This allows the noise to be cancelled out at the receiving end of the cable.
5) Ferrite Beads: Ferrite beads can be placed around cables to reduce EMI and RFI. Ferrite beads are cylindrical pieces of ferrite that are threaded over a cable. The ferrite material absorbs high-frequency noise, reducing the amount of noise that reaches the cable. This technique is particularly effective at reducing common-mode noise, which is noise that is picked up by both conductors of a cable.
These are some of the techniques that can be used to filter broadband noise while measuring spark plug voltage and current in an experimental ignition system. By using these techniques, the accuracy of the measurements can be improved, allowing for more accurate analysis of the ignition system's performance."
Most of these are common sense, but I didn't think of using #5 Ferrite beads to filter the broadband noise from the spark current. I've used these for HIRF filtering on the IAPS, but found that printed circuit board capacitors and inductance of circuit traces made a perfect zero cost (board layer count impact) LC filter (about a 2cm trace between ground planes right at the connector entry point). However it required the ground plane of the board to be connected to a low inductance ground return (that was the hard part). Ferrite beads if I recall start kicking in around 20MHz, and their Bode plots are based on continuous wave tests, so I don't know how they would work with the broad band RF from the spark.
I also did a search on the "magic box" for "measuring spark plug energy from ignition system", and got some hits on SAE papers that cost $35 unless you have a subscription.
The first part of the paper is a brief review of the techniques needed for measuring the voltage and current during the ignition process. These techniques have been used in test rigs and an engine to gain insights into the breakdown and subsequent discharge development.New correlations are presented
There are other search suggestions.
This may be of interest;
The secret to being able to capture and analyze secondary ignition waveforms is understanding what is happening in the coil and at the spark plug, and how the scope measures and graphs the voltages and ignition event.
This talks about a capacitive scope probe, which from reading the article is test equipment used in automotive repair. This must be some procurable piece of equipment.