Like H2OPWR, I am in it for the technology, though admittedly I started out because of gas prices.
The only gains I ever saw in my Saturn Vue, were due to the EFIE and not the HHO. I think until I get up around 5-6 LPM at a reasonable wattage, I won't see any gains from HHO. I do think the technology is viable, I just have to find the amount of HHO that will provide me the gains that are safe for the engine.
If I achieve better gas mileage then great. If not, then I have a portable HHO welding torch.
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Some days I get the sinking feeling that Orwell was an optimist!