CFM vs. displacement and CFM calc.

[TwinTurbo]

So after reading page after page these last few day I am wondering why we determine the amount of HHO necessary by engine size instead of how much air it moves? Since different engines of the same displacement use different amounts of air because they run at different RPM's, it seems that it would be more accurate to figure this way. For example, a 2L that runs between 2500 to 3000 rpm flows 66-79 cfm. but a higher reving one, say 3500-4000 flows 86-99 cfm. The rpms that the engine runs at for the majority of driving time will greatly influence the required amount of hho would it not? Is there an optimum ratio of HHO to intake air? Here is a link to a CFM calculator that also allows you to factor in Volumetric efficiency for NA or forced induction as well as two or 4 cycle engines. https://www.aiproducts.com/catalog/CFMCalculator.htm Your thoughts? I apologize if this as already been discussed, but I have yet to find anything about it.

[Stevo]

Good points and even more relevant when you consider the airflow based on horsepower. A 150 HP Ford Focus engine is going to flow a lot less than my 300HP turbocharged Subaru Boxer engine. I think that it is easier for most people to do the simple math: liters / 2 = x L/min. That is probably why it isn't discussed so much on these forums. I've always thought it to be mostly useless in determining your required injection volume, so trial by fire has been my approach. I think airflow relative to horsepower and displacement absolutely should be discussed more.

On the other hand.. I still believe that we should continue striving for a way to measure gas potency as not to nullify the above.

[BioFarmer93]

Stevo, excellent points..
I have a feeling that the "rule of thumb" of (liters / 2 = x L/min) probably emerged as a starting point for big, slow turning V-8's that typically got terrible mileage. We have observed often enough here that different folks are getting different results with less/more, wet/dry gas on the same type of engines & ignition systems. I have often thought that high revving engines needed some way to increase gas flow as rpm increased even more than their slower turning cousins. It might behoove us to do some fixed RPM testing with some known & well functioning reactor & engine (vehicle) combinations so that gas to rpm functionality (notice I didn't say efficiency :D) could be evaluated & determined.