That is a noble thing to do and I salute you for doing it. The reality is that your performance will be significantly diminished by the blood donation for some time. An average endurance trained man may have 5-6 units (.5 liter) of blood (blood volume increase is one of the effects of endurance training). When you donate a unit you’re down 10% in volume. The immediate effect will be similar drop in oxygen carrying capacity. The plasma will be replaced within a day or so. But the red blood cells can take up to a month to completely come back to the same level as before. During that time your aerobic performance will be negatively impacted.