var value = "AYRTON SENNA-12345678901";
var index = value.IndexOf('-');
var result = value.Remove(0, index + 1);
ou um split
var value = "AYRTON SENNA-12345678901";
var values = value.Split('-');
var result = values[1];
http://www.linkedin.com/pub/murilo-kunze/44/191/455