[dvldoc]

To really get better fuel economy you need at least a 10% to 15% gain in overall power. More power at less rpms is the only way to save on fuel, You will normally need to add alcohol to the mix if you want any real fuel savings, Good old washerfluid is great for doing the job.

If this is a turbo diesel then it should not be a problem to get this with just water, but if this is a gas N/A vehicle then it might be a strech to get the same power without adjusting timing.