Several ideas here that need to be thought about.
Read sfi spec you can have holes in tubes. The size of the hole depends on the diameter of tube. Mike, Monte's within rules.
There are many approaches to grounding. Floating grounds have their place and most of the time the term is misused. Many in the real electronic industry have different ideas. We used floating grounds in radio and tv. You have to isolate with test equipment. In the home ground requirements change every year.
If your negative battery bus is not tied to chassis it is not ground. Ground is related to earth ground and is made theough carbon in rubber tires. I could see where there may be benefits to using an isolated negative. This way no current is traveling through chassis. The main rail the crank trigger wire is in is a non current carrying ground, well actually if chrome moly a resister. Pretty slick, if you understand why you did it.
Two things.
Rulebook does state holes are legal, but "Visible reinforcement around any hole in any SFI Spec chassis (not just the roll cage) mandatory." Granted, Monte didn't build the chassis and it wasn't up to him to take care of that. And powdercoating is a pain to grind up and touch up after a weld repair, especially the vein stuff.
I believe earth in an automotive system is the negative post on the battery. I've always heard that if powerlines fall on your car, the rubber tires prevent you from being electrocuted as long as you don't step out and touch the ground. Using an isolated ground system like that makes the chassis basically inert as far as the electrical system is concerned. Not having stray current running through the chassis on something with a lot of noise sensitive electronics makes sense to me. Imagine a chassis constructed from a non-conductive material, it would need to have the same design ground system.
I also enjoy doing my electrical systems from scratch rather than any kits and have specific ways of doing things. I have no problem incorporating others' good ideas and techniques. None of mine have been on anything as complex as an EFI, traction-controlled, boosted car though. Still, there's a right way of doing things even on something stupid simple.
