To say that hydrogen doesn't improve your fuel efficiency, as well as emissions and overall engine life is...well....wrong.
It may not work on onboard HHO electrolysers but it most certainly will help if you have a supply of compressed Hydrogen.
The best part is......you can use virtually any fuel! That's right....Propane, CNG, Gas, old crappy gas, ethanol, methanol, diesel, etc. just by boosting it with hydrogen.
It also reduces emissions and is said to reduce heat and engine wear.
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KP and look for roy mcalister's videos. They are awesome.