When we put our ‘standard’ one size fits all HyCO 2DT (which we ordinarily use for 12-14 liter truck engines) on a 1.6 liter VW Jetta like this one http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=403the Jetta got a 40% increase in mileage when under load (traveling 70+ mph in Alberta).
BUT, when we installed our ‘standard’ one size fits all HyCO 2DT on a Class 8 truck, it’s power increased 14% in a dyno test… Which brought it to the MAXIMUM allowed by the engine manufacturer. If the power had increased any more, it WOULD have been grounds to void the engine warranty if anything went wrong with the engine (due to the power increase).
So, our experience says you can add enough HyCO 2DTs to equal 1 HyCO 2DT for each 2 liters of engine displacement. But… Keep the power increase consequences in mind, it’s your choice.