The natural gas engine company cut its guidance as customers sharply reduced inventory amid economic worries and delays in the availability of liquefied natural gas infrastructure.
Westport said it now expects revenue to come in between $340 million and $350 million, down from earlier guidance for between $400 million and $425 million.
The company earned $264 million in revenue in 2011.
"We have a strong balance sheet and our asset-light business model allows us to remain competitively positioned," Westport chief executive David Demers said in a statement.
"To help mitigate further contraction in overall transportation markets, we expect a number of key product launches in our automotive, trucking and off-road applications in 2013."
Westport is to release its financial results after the close of markets on Nov. 8.
The company announced deals earlier this year with General Motors and Caterpillar Inc.
The agreement with General Motors (NYSE:GM) will focus on light-duty vehicles, while the Caterpillar deal is for the development natural gas technology to fuel off-road heavy equipment that typically uses diesel.