HHO Generator Kit Comparison: Best Kits of 2025 Reviewed

What We Tested

Six HHO dry cell kits were bench-tested for LPM output per amp at target operating conditions (12A, KOH electrolyte, 25°C starting temperature). Each was also installed on a test vehicle and monitored for fuel economy change over 500 miles.

Best Overall: 9-Plate Dry Cell with PWM

The best-performing kit in our tests was a 9-plate 316L stainless dry cell bundled with a 30A PWM controller, dual EFIE, and bubbler safety kit. Output reached 1.1 LPM at 12A — 21% better than the closest competitor. The complete wiring harness with relay and 30A fuse made installation straightforward. Fuel economy improvement on test vehicle: 18%.

Best Budget: 6-Plate Basic Kit

The 6-plate entry-level kit ($65) produced 0.68 LPM at 12A — adequate for 4-cylinder engines up to 2.0L. Plate quality was acceptable (though the supplier's "316L" claim should be verified). The kit lacks PWM or EFIE, which limits real-world effectiveness on fuel-injected vehicles. Fuel economy improvement without EFIE: 3% (ECU compensation canceled most gains).

Best for Diesel: 12-Plate Heavy-Duty Kit

The 12-plate diesel kit produced 1.85 LPM at 20A — the highest output in our test. Diesel test vehicle (6.7L Cummins) showed 19% fuel economy improvement. No EFIE needed on diesel — the most plug-and-play result in the test group.

What to Look for When Buying

• Verified 316L stainless certification
• Included PWM controller and EFIE for gasoline applications
• Complete wiring harness with fuse and relay
• Bubbler included or available from same supplier
• Customer documentation of actual LPM output