I think that the US had already determined to enter the war by the time the Russian Revolution began, so there was little impact. If Russia had withdrawn from the war and the US had NOT entered it, then the outcome might have been different.
What many do not know is that the US sent troops to Russia to fight the Bolsheviks. The Americans were sent to Archangel, in northwest region. The British sent troops farther to the east.So, a related question would be: "What impact did USA and Britain have on the Russian Revolution?"
For more history on the American expedition to Russia, see: http://bentley.umich.edu/bhl/mhchome/polarb.htm