I have hho boosted my car for more than 10 months now. I was so impressed with the results that I wrote a small website to share what I have learned. I even wrote software to analyze my car OBD-II data.
Check my site at www.greenfuelbooster.com ... my design plans are free, my software is free. I mention other tools I used on the site.
As far as new people posting and then going away as mentioned. Well, I found this site to discuss HHO specifically. I've reviewed multiple design and found one that I can build myself to match all that was suggestive needed to be accomplished in order to gain the benefits: one is the O2 sensor I have a 1897 Suburban I subject with all my experiments with save saving techniques. The HHO is by far the most efficient idea I've found. Thus far, I only have city driving data for MPG. I get 14MPG city with one HHO constructed from SS light switch cover from hardware store, PVC pipe and the necessary electrical system to run it. The cell consist of six light switch plates -NPPN- using SS hose clamp as the lead with shrink tube around the leads. All of these is housed in 4" PVC with rubber end cap and quick release access end cap at the other end with a wing nut. The O2 sensor I selder an extra sensor fitting which took the sensor away from the exhaust flow.