I have been trying to build HHO generators for some time without much success. I do have success tho with a Zero PMW. The recurring problem I see is that introducing O2 with the Hydrogen causes the sensors to inject more fuel to overcome the excess. and then we have to compensate with EEIFE. Recently, in my web searching on the subject, I ran across the fuelcellstore.com web site. There is a "stack on" unit AS15 that produces .25 L of pure Hydrogen per minute at 7amp 12V. O2 is produced in another chamber. This is 15 L Hydrogen per hr and 7.5 L O2 per hr. Not much .75 L of HHO per minute. BUT, if only Hydrogen is introduced into the intake, there will be no need to try to fool the computer.

These units can be chained or "stacked" for more production. The store is dedicated to fuel hydrogen cells and also sells a pressurization tube for 30 psi output. These are cheaper than most units I've seen.