The grounding subject has been brought up before.
Due to many possible issues, when wiring a race car, especially with EFI and electronics, you should avoid grounding to the chassis and/or engine. The best approach is a single grounding location for all the electrical and components, directly to the battery ground.
Since several ground points will creates a ground loop it is probably the reason why the car that was mentioned earlier magnetized.
You are asking the chassis and engine block to carry electrical loads and DC power requires to travel both ways, positive and negative. When you have a single point for all the grounds to the battery you are minimizing the chances to have a grounding issue.
When you have a ground loop, most electronics do not behave properly because the reference to ground is different and can make a sensor output measure incorrectly.
A friend of mine that builds chassis cars such as Top Sportsman and Comp Eliminator cars, had issues with some of the electronics on the new cars and he kept adding grounds. After he called me to ask about the issue, I suggested he used a single point ground. After doing so, all the issues went away.
Just remember, in the early days, we had carburetors and points distributors, and later on, electronic distributors. Nowadays, the cars are loaded with all kinds of ignition boxes, EFI and electronics, therefore, the electrical power demands have increased exponentially and just adding additional or higher voltage batteries does not solve the issue. Many chassis cannot ground properly because of corrosion, paint, rubber isolators, etc...
Although I do not support the product they sell, the link below has some great information and guidance about race car electrical systems.
"https://moretraction.com/2018/12/31/2416/"