I have been playing with electrical things since I was 10 years old or so, now I am 52, retired from the USN in electronics, was a union electrician, etc.
Though I have not conducted my own scientific tests I have seen dyno runs with some minor improvements from reliable sources. BUT, very very minor. I thought this over and decided on my last project car to do some testing in a limited way, seat of the pants, made a simple 8 gauge kit, you could hardly tell it was there, the car ran just the same to me, took it off, tried other locations, not a bit of percieved improvement. '
This was on a 1ZZ with 13PSI and stock internals, it was quite fast but I raced it often(only time I usually drove it) and believe I could tell if it ran better, had more power, etc. but it did not to me.
I must say I also had already upgraded the battery to alt wire to 4 gauge and the bat ground to chassis and block to 4 gauge as well, this is the most imporatant you can do. I was setting it up for a big audio install I never got around to, had to much fun racing instead
Rick