looking for input on an HHO system

[rollertoaster]

Ok, this is my first post here, so go easy on me. I'm looking to boost the fuel economy of my 06 Honda Element AWD AT. I do what I can to improve my mileage, but my lifestyle contradicts it a bit. I'm an avid mountain biker, which means I usually have gear in my car, and bikes on the rack. I run my tires at about 35psi, and take my rear seats out of the car most of the time.

I drive 33mi each way to work and I drive too fast. I average between 20-22mpg. My mileage was better before the switch to ethanol mix. I turbo'ed the element last winter, and believe it or not it did not negatively affect my mileage. Basically, I've more than doubled my power with the same gas mileage. Now I'd like to improve my mileage and keep my horsepower. I have a piggyback computer on the car and a wideband a/f meter, so I can alter my A/F ratio to whatever I want, retard my timing etc...

I want to build an HHO generator to supplement my fuel usage. I want to system to only inject under part load (no idle or boost). My injectors are large at 650cc, and I can not decrease my duty cycle any further at idle. I don't want to add any during boost because I like my pistons and I don't want any holes in them. What kind of a/f ratio do I need to run with a HHO mixture?

Ok, so lets say at highway speed (70mph) my injector duty cycle is at 7-9% engine speed around 3000rpm. at my fuel pressure, that would equate to approx 180-200cc/min. How much HHO do I need to generate? I'm still reading up on HHO cells and I don't know what type to build yet, but I do not want it to draw more than 20 amps. I will be using a PWM regulator on the generator.

that's all I can think of for now. I'll update this more later as I think of more.