2000 Chevy Cavalier 2.2 automatic. This is the one that I got 129 miles to a gal. out of. I used the dimmer switch from a old Toyota truck and a couple diodes. Went through a few however, they burn up at that 5. volt mark. The car would stall or buck if under a moderate to heavy load under 3.5-3.75 volts. But the sweet spot was 4.5 volts. Heavy acceleration or upgrades would need 7-9 volts. Coasting at 70 on flat highway or downhill, I would turn off the fuel pump completely and still be running normal, between 2800-3400 rpm, no engine light, all normal on the scanner outside of the O2's being blank or next to.
By the way, the cars fuel injected, in tank pump, federal emissions, 223,000 miles. No modifications outside the HHO and fuel pump power being limited. No efie, map enhancer, nothing. But it's now our daughter's car back to original.
Its done right or its not done !
Hail HHO.