Sigh... You know the basic underlying concept of the kit, is based on a good practice of grounding everything to a central point. And this is where it starts on the marketing of them.
However, you have to treat the ignition system a bit differently. Due to the fast rise times of the pulses, it's important to keep the high voltage spark circuit as short as possible. So a separate coil for each cylinder mounted close to the spark plug means the path is short through the wire to the plug and then the return path is through the head. So a ground wire shouldn't impact this energy side of the ignition at all, as it's an isolated circuit. (more or less, other than impedance effects through the coil to the primary) The shorter, the better to make sure the rise time of the pulse is as steep as possible and current once the arc is drawn, is the maximum due to the lowest impedance possible at the frequencies that make up the pulse.
Yet at the same time, the coil leads these days are resistor type, to slow this pulse edge down, so I suppose the trade off is keeping the noise down. Slowing this down, removes the higher frequency energy to reduce the chance of ignition noise. The shorter path of the coil being close to the plug, would also reduce this noise. (It also means the coil can recover in time for the next ignition pulse at high rpm, better, which is another reason to have a coil on each plug.)
So how would the ground wire affect this? It shouldn't... On the primary side of the coil, there should be already be a substantial ground path through the same ground wire that's used to allow the starter current needed to start the engine.
I'm just trying to work this through in my head, yet again... I've seen these kits before and every time I go through this, I've yet to find anyone who can truly explain why one of these kits would work, if the automobile is already properly designed. I have good confidence in Nissan's design, especially the engine and it's systems, as it's very well put together.
Any EE's with RF experience, or Physicists want to comment on this? I love being proved wrong, as it usually means I've learned something in the process.
b0xdesigns, I apologise if my first comments came off as disrespectful, I must admit, I did overreact, due to previous visits with those grounding kits, and my opinion of them...
In the meantime, I'm going to send a note to the Admin about the pictures... It's annoying when they give links instead of showing up. This happened in the Nav section too, with Generator's post and we got that fixed.