The only way to increase your water pressure is to install a pump. A common misconception is that smaller pipe will increase your water pressure. Actually the opposite is true. What causes the water to squirt further when you put your finger over the end of the hose is velocity, which will not improve the sprinklers performance. The only way your water pressure will increase from what you start with at the water meter or well head is to go downhill. Keep in mind your water pressure deceases at the same rate going uphill. You gain or lose .43 PSI per foot of vertical fall or rise. So, the trick is to hold onto as much pressure as you can. Minimizing your pressure loss is all you can do. One way you do this is to use larger, not smaller pipe. This minimizes the drag on the water and you get more water to the sprinkler heads with a minimum of pressure drop.
If you have any more questions please call or stop by, we would be happy to answer them.