[BLSTIC]

Well lets see. The project car weighs about 1100kg (incredibly light by modern standards). The hyrogen system weighs 10kg all up, absolute max (this is bubbler and electrolyser, both full of water. No automatic filling system. Wiring weight is negligible). This is around 1% of the mass of the car. Assuming zero energy recovery (through longer coast distances) it would take 1% more energy to accelerate the car, and nothing to keep in moving (1% change in mass would be undectible when it comes to rolling resistance). Under a worst case scenario (such as continous accelleration, or uphilll) the system will use 1% more fuel through mass alone.

If it makes 1% difference in economy. Even if I carried around an extra 20L of water (standard jerry can size) the MAXIMUM weight induced penalty would be 3%.

I would say that if the system changes combustion at all it will be worth the weight penalty.

That said, you all have to wait (until after I have converted my prelude loom from OBD1 to OBD2b plugs so I can use the (not so) plug in link that's in the shed) for results