How Much HHO

Revised 7 Feb 2012

First of all, let me start out by making a bold statement: Nearly all users of HHO systems are using too much HHO.

I frequently get asked about how much HHO will yield the best mileage gains for a particular car or truck. Years ago, we used the following formula: 1/4 liter per minute for each liter of engine size. For example, if you have a 2 liter engine, you need .5 LPM of HHO. In practice this is a pretty good formula to use, because most people measure HHO using ball meters or pop bottle test. These tests are not particularly accurate, and tend to read higher flow rates than actual. So with this in mind, the formula will work pretty well.

We have since found that the correct amount of HHO to use is closer to 1/8 of a liter per minute per liter of engine size. But the measurement of HHO flow must be made with more precise equipment calibrated for HHO. We have a flow meter from Alicat Scientific. It costs $1,500 retail, and has been calibrated for HHO specifically (as well as about 40 other gasses). It compensates the flow reading for 72 degrees Fahrenheit, no matter what the actual gas temperature is. When we compare the readings from the Alicat, to a ball meter, we find that the ball meter shows approximately double the flow rate as the Alicat. Pop bottle testing will also show higher flow rates than actual.

Now while it's true that some cells are more efficient than others, the difference isn't really very much, despite the wide divergence in reports from the manufacturers. In most cases, the difference is due to inaccuracies in the measurement process. In some cases, manufacturers will report wildly high flow rates. They probably aren't lying about what they read on their flow meters. However, in these cases you will find that they are over-driving their cells and making very hot output gas that includes a lot of steam. Just the fact of being hot will fool the flow meter, and can double the "flow rate". But this isn't actually more HHO. Its just a hotter gas which, because its expanded, will show an apparently higher volume. That coupled with the steam makes the gas much less effective at improving mileage than another cell producing 1/4 of the volume, but more HHO per amp. If you can't comfortably hold you hand on your cell after it has warmed, then it's a steamer.

So, given that the cell isn't being overdriven (we call these cells "steamers"), you can actually get pretty close to the correct amount of HHO by the amount of amps you draw. If the cell is drawing about 5 amps, that will work on a 1.5 to 1.8 liter engine. 12 amps will work fine on a 5 Liter engine, and 15 amps will work on larger 6 and 7 liter engines. For 15 liter semi trucks, we use 1.25 - 1.5 LPM, and we run at about 25 amps to get it.

In actual practice you should try adjusting your amperage to see which gives you the best mileage gains. There can be some variance in cell efficiency. But you will find that the correct amount of HHO will give you the best gain in MPG, and that more HHO will start to reduce that mileage. Add more and more HHO, and you can end up with lower mileage than when you started. We'll explain why further on in this article.

As another note, some suppliers get their cells tested and certified by the IHHOI (International HHO Institute). You can use the 1/8th LPM formula with these results, because they use an Alicat Scientific flow meter as described above for all of their flow testing. The results posted by the IHHOI people are the only ones I've seen that aren't inflated. Nearly all suppliers feel they have to show inflated numbers because otherwise their cell "isn't as good" as the other suppliers with inflated numbers. The whole industry is currently working on false standards of flow rate and efficiency. But you can undercut that in 2 ways: 1) Deal with suppliers who are certified by the IHHOI, or 2) Use amperage as your gauge of how much HHO to use, provided that the cell doesn't run hot to the touch after running for a while.

More Is Better, Right?

People new to this subject think that if some HHO is good, more is always going to be better. Others believe that the electricity used to make the HHO is actually "free energy" since the engine is turning anyway. Both of these statements are false, as I will describe below.

First lets look at the alternator. When the engine is running it transfers rotational energy, via a belt to the alternator, which then generates electricity. This energy is actually a measurable drag on the rotational energy of the engine, and it costs fuel to counter this drag. Even if you're coasting down hill, the distance you will coast will be less before you have to add gas again to maintain your speed. The bottom line? The electrical energy from your alternator costs you gas to create.

Now lets look at the gas. HHO, when burned, does not give back as much energy as the energy that was used to create it. There are several energy conversions involved. Since there is no such thing as 100% efficiency, energy is lost at each conversion. The conversions are: mechanical to electrical (alternator), electrical to chemical (electrolyser), and chemical to mechanical (burning the HHO). By the time all 3 of these conversions have taken place, when the HHO burns you'll get back about 20-25% of the energy used to create it. But don't despair just yet. Awesome gains in mpg are still achievable using this technology.

Where we get our gains is the fact that the HHO causes the gas to burn more efficiently. The majority of the energy in our petroleum fuel is wasted due to incomplete combustion during the power stroke. The HHO causes some of this waste to be used in the combustion process. We're not actually getting it all back either. It's just that there's so much waste, that even getting part of it recovered makes a large change in our mileage. This is what makes HHO so valuable in our engines.

However, only so much HHO will give us more efficiency in this way. If you add more HHO after that, you'll then start to lose mileage because of the efficiency losses described above. Now, as you add more and more HHO, your mileage gains will start to dwindle away. Now you'll be drawing more and more horsepower to make amperage, than you get back when the HHO burns. Since you've already tapped the latent power in the petroleum fuel, and since more HHO doesn't help you recover any more of the petroleum fuel's power, the overall result is that your mileage will diminish.

How Much HHO?

Since good accurate measurement of HHO flow is not available to the average user, we have provided an alternate way to work with this data. All things being equal, the HHO production is directly proportional to the amps.

What do I mean by "all things being equal"? There are a number of factors that have to be true in order for the chart below to be valid. First of all, you have to have a cell that is sized for the size of engine you have. For instance if you have a 6" dry cell with 7 plates and try to put it on a 25 liter engine, you will need to over-drive it to get the amps you need. You will be making a lot of steam. It will be inefficient. The chart will not work in that circumstance. Or another example: You build a home made cell from switch plate covers that you found online, and it has 2 neutral plates and some partial shorting across the plates. This is an inefficient cell and the chart below will not apply. But given a good reputable dry cell from a manufacturer that knows what he's doing, the charts below will apply. These charts work for our cells, and most good reputable cell manufacturers make a cell that is comparable.

Therefore this chart can be used to get your starting amp draw. Use this as a starting point. Test with more amps. Test with less amps. Let it run for a while so your engine can clean itself out, and then try again with more and less amps. Run for a full tank with each setting. Adjust to maximize your fuel mileage gains. Over time you will find the ideal amount of amps for your engine, driving conditions and driving habits.

Engine Size Liters12V Amps24V AmpsLPM


So, by trial and error of many years, many researchers in the HHO industry have adopted the formulas above. I hope I have helped you in your quest to get the best mileage from your vehicle. If you have more questions on this subject, please post them at our forum:

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