[straight5]

To the OP, I agree with you, that there are a lot of people out there that make claims of efficiency improvements - some small - some large. I don't doubt that some (at least a few) are real. Many of these claims are by people who seem to be quite knowledgeable and sincere. Those people generally aren't selling anything and it seems as if they have nothing to gain by convincing other people, except for the satisfaction of knowing that they have helped someone else.
I don't know what the real answers are.
There are probably a few that have made significant gains, but exactly how and why - I suspect that often they themselves don't understand the reasons.
.....Maybe another part of the equation is that people think that because "X" helped my mileage, then "X" will help yours - when we know that may not be the case at all.
Take Somender Singh's groove theory. Don't you think that his "grooves" would help in some instances, but would be detrimental in more cases than they helped?
Please don't think that I am trying to discourage you. I hope that you read what these guys have said and carefully consider the comments. People on this forum seem to me to be very willing to help others and I've been surprised many times at the time, effort, knowledge and resources that are freely shared here.
BTW - I still don't understand why there is generally no gain in mpg by introducing into an engine a small amount of browns gas, HHO, or whatever - unless of course you're using the alternator to power the device making it.