Yes. No.

Although there is some guy who used to post over in the diesel section about how he gets over 50mpg in a homebuilt HHO unit and 100mpg with an HHO motorcycle. YMMV. I've messed around with some setups before and while its cool and fun to tinker with, it doesn't really do anything. You're still using energy off of the alternator to produce the electricity to electrolyze the water which is a greater resistance on the engine anyway. Based on physics and chemistry (i.e. conservation of matter), it simply doesn't work.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth