An investor group boosted its bid for Conrail.

Conrail Acquisition Corp., led by First Boston Corp., raised its bid for Consolidated Rail Corp. to $1.8 billion from $1.65 billion, putting new pressure on Congress to reject a Reagan Administration plan to sell the federally owned freight railroad to Norfolk Southern Corp. for $1.2 billion. Conrail Acquisition, the group organized by the New York investment firm to bid for Conrail, said the amended offer was based on Conrail’s strong financial performance last year, when it made $442 million.