Here's a couple of links about the hydroxy boosters. As many of you probably know, they don't actually make straight hydrogen gas but HHO gas (hydroxy >>> 2 hydrogens with 1 oxygen).
http://www.smacksboosters.110mb.com/
New Release of OU Electrolyzer Plans
I am going to start gathering the parts for a Smackbooster today, but I am starting out with putting it on my Ranger's 230k mile V-6.
Here are a couple links to Powerstrokes with them.
This one is a '01 E350 van, there is a lot of info there, but it's a little sketchy about the details.
Report:Robert Pritchett's Mileage Results from Hydroxy Boost Addition - PESWiki
These two are You-Tube videos from a guy who built and installed one in a '02 Powerstroke pickup.
testing
YouTube - 14 cell hydrogen generator
installed
YouTube - 14 cell hydrogen generator installed
It sounds like you need a PWM (pulse width modulation) device to be able adjust the current through the Booster for best gas production, but they are available, and I don't think a lot of money. On the fuel injected gas engines with computers, sounds like you also have to be able to override the O2 sensor, or possibly get what they are calling a EFIE device (I think this means electronic fuel injection enhancer, but not postive about this). On the diesels, have not found out what, if anything, you have to do concerning the computer. (As you know, be discerning about what you read about and see on the internet.)
Now you basically know what I know about it, which ain't much.