UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (date of earliest event reported): May 25, 2016

FUEL SYSTEMS SOLUTIONS, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (646) 502-7170

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

On May 25, 2016, Fuel Systems Solutions, Inc., a Delaware corporation (“Fuel Systems”), announced that the final exchange ratio has been determined for its proposed merger with Westport Innovations Inc. (“Westport”) and also reaffirmed the Fuel Systems Board of Directors’ recommendation to vote in favor of the proposed merger.

Fuel Systems stockholders will receive 2.4755 shares of Westport common shares for each share of Fuel Systems common stock owned upon completion of the merger, assuming the merger closes as anticipated on June 1, 2016. Under the amended merger agreement, the exchange ratio was calculated based on the volume weighted average price of Westport common shares on the Nasdaq Stock Market, as reported by Bloomberg, for the ten consecutive trading days ended on and including May 24, 2016 (the trading day five business days prior to June 1, the anticipated closing date of the merger).

As previously announced, if the merger is completed pursuant to the amended merger agreement, each share of common stock of Fuel Systems outstanding immediately prior to the effective time of the merger will be cancelled and automatically converted into the right to receive a number of Westport common shares equal to the exchange ratio. The value of any fractional interests of Westport common shares to which a holder of Fuel Systems common stock would otherwise be entitled will be paid in cash as provided in the amended merger agreement.

A copy of the press release issued by Fuel Systems is included as Exhibit 99.1 hereto, and is incorporated herein by reference.

Additional Information and Where to Find It

Fuel Systems has filed a revised proxy statement/prospectus with the U.S. Securities and Exchange Commission (the “SEC”). INVESTORS AND STOCKHOLDERS ARE URGED TO READ THE REVISED PROXY STATEMENT/PROSPECTUS, AND OTHER RELEVANT DOCUMENTS FILED WITH THE SEC, IN THEIR ENTIRETY CAREFULLY BECAUSE THEY CONTAIN IMPORTANT INFORMATION ABOUT WESTPORT, FUEL SYSTEMS, THE PROPOSED TRANSACTIONS AND RELATED MATTERS. Investors and stockholders are able to obtain free copies of the revised proxy statement/prospectus and other documents filed with the SEC by the parties through the website maintained by the SEC at www.sec.gov. In addition, investors and stockholders are able to obtain free copies of the revised proxy statement/prospectus and other documents filed with the SEC by the parties by contacting Westport Investor Relations at 1-604-718-2046 or invest@westport.com (for documents filed with the SEC by Westport) or Fuel Systems’ Investor Relations advisors, LHA, at 1-415-433-3777 or fuel@lhai.com (for documents filed with the SEC by Fuel Systems).

Participants in the Solicitation

Westport, Fuel Systems and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from the stockholders of Fuel Systems in respect of the proposed transactions contemplated by the revised proxy statement/prospectus. Information regarding the persons who are, under the rules of the SEC, participants in the solicitation of the stockholders of Fuel Systems in connection with the proposed transactions, including a description of their direct or indirect interests, by security holdings or otherwise, is set forth in the revised proxy statement/prospectus filed with the SEC. Information regarding Westport’s directors and executive officers is contained in Westport’s Annual Report on Form 40-F for the year ended December 31, 2015, and its Management Information Circular, dated March 11, 2015, which is filed with, in the case of the Annual Report on Form 40-F, and furnished to, in the case of the Management Information Circular, the SEC and can be obtained free of charge from the sources indicated above. Information regarding Fuel Systems’ directors and executive officers is contained in Fuel Systems’ Annual Report on Form 10-K for the year ended December 31, 2015 and its Proxy Statement on Schedule 14A, dated April 14, 2015, each of which are filed with the SEC and can be obtained free of charge from the sources indicated above.

Cautionary Note Regarding Forward Looking Statements

This filing contains forward-looking statements within the meaning of the U.S. federal securities law. Words such as “anticipates”, “believes”, “expects”, “intends”, “will”, “should”, “may”, and similar expressions may be used to identify forward-looking statements. Forward-looking statements are not statements of historical fact and reflect the Fuel Systems’ and Westport’s current views about future events. This filing contains forward-looking statements, including statements regarding the merger, the timing for the anticipated closing of the merger, the timing of the Fuel Systems stockholders meeting and related matters. These statements are neither promises nor guarantees,

but involve known and unknown risks and uncertainties and are based on both the views of management and assumptions that may cause our actual results, levels of activity, performance or achievements and ability to complete the proposed merger with Westport to be materially different from any future results, levels of activities, performance or achievements expressed in or implied by these forward looking statements. These risks and uncertainties include risks and assumptions related to our revenue growth, operating results, industry and products, the general economy, conditions of and access to the capital and debt markets, governmental policies, regulation and approvals, technology innovations, fluctuations in foreign exchange rates, operating expenses, the availability and price of natural gas, global government stimulus packages, the acceptance of and shift to natural gas vehicles, the relaxation or waiver of fuel emission standards, the inability of fleets to access capital or government funding to purchase natural gas vehicles, the development of competing technologies, our ability to adequately develop and deploy our technology, the actions and determinations of our joint venture and development partners, as well as other risk factors and assumptions that may affect our actual results, performance or achievements or financial position discussed in Westport’s Annual Report on Form 40-F for the year ended December 31, 2015, and Fuel Systems’ Annual Report on Form 10-K for the year ended December 31, 2015, and other filings made by the companies with securities regulators. Readers should not place undue reliance on any such forward-looking statements, which speak only as of the date they were made. We disclaim any obligation to publicly update or revise such statements to reflect any change in their expectations or in events, conditions or circumstances on which any such statements may be based, or that may affect the likelihood that actual results will differ from those set forth in these forward looking statements.

(d) Exhibits

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.