REGISTRATION RIGHTS AGREEMENT

Exhibit 10.10

REGISTRATION RIGHTS AGREEMENT

This Registration Rights Agreement (the “Agreement”) is made and entered into as of this 29^th day of April, 2011 by and among Power Solutions International, Inc., a Nevada corporation (the “Company”), and Gary Winemaster, Kenneth Winemaster and Thomas Somodi (the “Stockholders”).

The parties hereby agree as follows:

1. Certain Definitions.

As used in this Agreement, the following terms shall have the following meanings:

“Business Day” means a day, other than a Saturday or Sunday, on which banks in New York City are open for the general transaction of business.

“Common Stock” means the Company’s common stock, par value $0.001 per share, and any securities into which such shares may hereinafter be reclassified.

“Investors” means the Stockholders and any transferee of any Investor who is a subsequent holder of any Registrable Securities and who complies with the provisions of Section 6(c).

“Person” means an individual, a limited liability company, a partnership, a joint venture, a corporation, a trust, an unincorporated organization or a government or any department or agency thereof or any other legal entity.

“Private Placement Investors” means the “Investors” as such term is defined and used in the Private Placement Registration Rights Agreement.

“Private Placement Registrable Securities” means the “Registrable Securities” as such term is defined and used in the Private Placement Registration Rights Agreement.

“Private Placement Registration Rights Agreement” means that certain Registration Rights Agreement, dated as of even date herewith, by and among the Company, the investors named therein and Roth Capital Partners, LLC.

“Prospectus” means (i) the prospectus included in any Registration Statement, as amended or supplemented by any prospectus supplement, with respect to the terms of the offering of any portion of the Registrable Securities covered by such Registration Statement and by all other amendments and supplements to the prospectus, including post-effective amendments and all material incorporated by reference in such prospectus, and (ii) any “free writing prospectus” (as defined in Rule 405 under the 1933 Act) relating to any Registration Statement.

“Register,” “registered” and “registration” refer to a registration made by preparing and filing a Registration Statement or similar document in compliance with the 1933 Act (as defined below), and the declaration or ordering of effectiveness of such Registration Statement or document.

“Registrable Securities” means (i) any shares of Common Stock held by any of the Investors, or issuable upon exercise, conversion or exchange of any securities held by any of the Investors, at any time on or after the date hereof, and (ii) any other securities issued or issuable with respect to or in exchange for any such shares of Common Stock, whether by merger, charter amendment or otherwise; provided, that a security shall cease to be a Registrable Security upon (A) sale pursuant to a Registration Statement or Rule 144 under the 1933 Act, or (B) such security becoming eligible for sale without restriction or limitation by the Investor holding such security pursuant to Rule 144.

“Registration Statement” means any registration statement of the Company filed under the 1933 Act that covers the resale of any of the Registrable Securities pursuant to the provisions of this Agreement, amendments and supplements to such Registration Statement, including post-effective amendments, all exhibits and all material incorporated by reference in such Registration Statement.

“Required Investors” means the Investors holding at least 66 2/3% of the Registrable Securities. For purposes of this definition, an Investor shall be deemed to hold any Registrable Securities then issuable upon conversion, exercise or exchange (as applicable) of any securities held by such Investor.

“SEC” means the U.S. Securities and Exchange Commission.

“1933 Act” means the Securities Act of 1933, as amended, and the rules and regulations promulgated thereunder.

“1934 Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder.

2. Rights to Piggyback Registration.

(a) If, at any time following the date of this Agreement that any Registrable Securities are outstanding, the Company proposes for any reason to register any shares of Common Stock under the 1933 Act (other than pursuant to a registration statement on Form S-4 or Form S-8 (or a similar or successor form) or pursuant to Section 2(a) of the Private Placement Registration Rights Agreement) with respect to an offering of Common Stock by the Company for its own account or for the account of any of its shareholders, it shall at each such time promptly give written notice to the holders of the Registrable Securities of its intention to do so (but in no event less than fifteen (15) days before the anticipated filing date) and, to the extent permitted under the provisions of Rule 415 under the 1933 Act, include in such registration all Registrable Securities with respect to which the Company has received written requests for inclusion therein within fifteen (15) days after receipt of the Company’s notice (a “Piggyback Registration”). Subject to Section 2(c), such notice shall offer the holders of the Registrable Securities the opportunity to register such number of shares of Registrable Securities as each such holder may request and shall indicate the intended method of distribution of such Registrable Securities.

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(b) Notwithstanding the foregoing, (i) if a Piggyback Registration is an underwritten public offering, the Investors must sell their Registrable Securities to, if applicable, the underwriter(s) at the same price and subject to the same underwriting discounts and commissions that apply to the other securities sold in such offering (it being acknowledged that the Company shall be responsible for other expenses as set forth in Section 2(d)) and subject to the Investors entering into customary underwriting documentation for selling shareholders in an underwritten public offering, and (ii) if, at any time after giving written notice of its intention to register any Registrable Securities pursuant to Section 2(a) and prior to the effective date of the registration statement filed in connection with such registration, the Company shall determine for any reason not to cause such registration statement to become effective under the 1933 Act, the Company shall deliver written notice to the Investors and, thereupon, shall be relieved of its obligation to register any Registrable Securities in connection with such registration.

(c) Notwithstanding the foregoing, (i) if a Piggyback Registration is an underwritten primary registration on behalf of the Company (including any such offering that is also proposed to include securities to be sold on behalf of holders thereof) and the managing underwriters advise the Company in writing that in their opinion the number of securities requested to be included in the registration jeopardizes the marketing of the proposed offering, the Company will include in such registration: first, the securities that the Company proposes to sell and the Private Placement Registrable Securities requested to be included in such registration by the Private Placement Investors, second, the Registrable Securities and any other shares of Common Stock requested to be included in such registration pursuant to registration rights substantially similar to those set forth herein, pro rata among the Investors and the holders of such other shares on the basis of the number of Registrable Securities and shares of Common Stock owned by the Investors and such holders, respectively, with further successive pro rata allocations among the Investors and such holders if any such Investor or holder has requested the registration of less than all of the Registrable Securities or shares of Common Stock such Investor or holder, as applicable, is entitled to register, and third, any other securities requested to be included in such registration; or (ii) if a Piggyback Registration is an underwritten secondary registration solely on behalf of holders of the Company’s securities (other than the Private Placement Investors) and the managing underwriters advise the Company in writing that in their opinion the number of securities requested to be included in the registration jeopardizes the marketing of the proposed offering, the Company will include in such registration: first, the securities requested to be included therein by the holders requesting such registration, the securities that the Company proposes to sell, and the Private Placement Registrable Securities requested to be included in such registration by the Private Placement Investors, second, the Registrable Securities and any other shares of Common Stock requested to be included in such registration pursuant to registration rights substantially similar to those set forth herein, pro rata among the Investors and the holders of such other shares on the basis of the number of Registrable Securities and shares of Common Stock owned by the Investors and such holders, respectively, with further successive pro rata allocations among the Investors and such holders if any such Investor or holder has requested the registration of less than all of the Registrable Securities or shares of Common Stock such Investor or holder, as applicable, is entitled to register, and third, any other securities requested to be included in such registration.

(e) The Company will pay all expenses associated with each registration, including filing and printing fees, the Company’s counsel and accounting fees and expenses,

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costs associated with clearing the Registrable Securities for sale under applicable state securities laws and listing fees, but excluding fees and expenses of any counsel to the Investors and discounts, commissions, fees of underwriters, selling brokers, dealer managers or similar securities industry professionals with respect to the Registrable Securities being sold.

3. Company Obligations. The Company will use commercially reasonable efforts to effect the registration of the Registrable Securities in accordance with the terms hereof, and pursuant thereto the Company will:

(a) provide copies to and permit counsel designated by the Investors to review each Registration Statement and all amendments and supplements thereto no fewer than three (3) Business Days prior to their filing with the SEC and not file any document to which such counsel reasonably objects;

(b) furnish to the Investors and their legal counsel (i) promptly after the same is prepared and publicly distributed, filed with the SEC, or received by the Company (but not later than two (2) Business Days after the filing date, receipt date or sending date, as the case may be) one (1) copy of any Registration Statement and any amendment thereto, each preliminary prospectus and Prospectus and each amendment or supplement thereto, and each letter written by or on behalf of the Company to the SEC or the staff of the SEC, and each item of correspondence from the SEC or the staff of the SEC, in each case relating to such Registration Statement (other than any portion of any thereof which contains information for which the Company has sought confidential treatment), and (ii) such number of copies of a Prospectus, including a preliminary prospectus, and all amendments and supplements thereto and such other documents as each Investor may reasonably request in order to facilitate the disposition of the Registrable Securities owned by such Investor that are covered by the related Registration Statement;

(c) prior to any public offering of Registrable Securities, use commercially reasonable efforts to register or qualify or cooperate with the Investors and their counsel in connection with the registration or qualification of such Registrable Securities for offer and sale under the securities or blue sky laws of such jurisdictions requested by the Investors and do any and all other commercially reasonable acts or things necessary or advisable to enable the distribution in such jurisdictions of the Registrable Securities covered by the Registration Statement; provided, however, that the Company shall not be required in connection therewith or as a condition thereto to (i) qualify to do business in any jurisdiction where it would not otherwise be required to qualify but for this Section 3(c), (ii) subject itself to general taxation in any jurisdiction where it would not otherwise be so subject but for this Section 3(c), or (iii) file a general consent to service of process in any such jurisdiction;

(d) use commercially reasonable efforts to cause all Registrable Securities covered by a Registration Statement to be listed on each securities exchange, interdealer quotation system or other market on which similar securities issued by the Company are then listed;

(e) promptly notify the Investors upon (i) the issuance of any stop order with respect to, or other suspension of effectiveness of a Registration Statement, (ii) discovery that, or

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upon the happening of any event as a result of which, the Prospectus includes an untrue statement of a material fact or omits to state any material fact required to be stated therein or necessary to make the statements therein not misleading in light of the circumstances then existing, or (iii) the Company’s determination to delay the disclosure of material non-public information concerning the Company, the disclosure of which at the time is not, in the good faith opinion of the Company, in the best interests of the Company; and

(f) otherwise use commercially reasonable efforts to comply with all applicable rules and regulations of the SEC under the 1933 Act and the 1934 Act, including, without limitation, Rule 172 under the 1933 Act, file any final Prospectus, including any supplement or amendment thereof, with the SEC pursuant to Rule 424 under the 1933 Act, promptly inform the Investors in writing if, at any time during the Effectiveness Period, the Company does not satisfy the conditions specified in Rule 172 and, as a result thereof, the Investors are required to deliver a Prospectus in connection with any disposition of Registrable Securities and take such other actions as may be reasonably necessary to facilitate the registration of the Registrable Securities hereunder; and make available to its security holders not later than the Availability Date (as defined below), an earnings statement covering a period of at least twelve (12) months, beginning after the effective date of each Registration Statement, which earnings statement shall satisfy the provisions of Section 11(a) of the 1933 Act, including Rule 158 promulgated thereunder (for the purpose of this subsection 3(f), “Availability Date” means the 45th day following the end of the fourth fiscal quarter that includes the effective date of such Registration Statement, except that, if such fourth fiscal quarter is the last quarter of the Company’s fiscal year, “Availability Date” means the 90th day after the end of such fourth fiscal quarter).

4. Obligations of the Investors.

(a) Each Investor shall furnish in writing to the Company such information regarding itself, the Registrable Securities held by it and the intended method of disposition of the Registrable Securities held by it, as shall be reasonably required to effect the registration of such Registrable Securities and shall execute such documents in connection with such registration as the Company may reasonably request. At least five (5) Business Days prior to the first anticipated filing date of any Registration Statement, the Company shall notify each Investor of the information the Company requires from such Investor if such Investor elects to have any of the Registrable Securities included in the Registration Statement. An Investor shall provide such information to the Company at least two (2) Business Days prior to the first anticipated filing date of such Registration Statement if such Investor elects to have any of the Registrable Securities included in the Registration Statement.

(b) Each Investor, by its acceptance of the Registrable Securities agrees to cooperate with the Company as reasonably requested by the Company in connection with the preparation and filing of a Registration Statement in which such Investor has requested inclusion of any of its Registrable Securities pursuant to Section 2(a).

(c) Each Investor agrees that, upon receipt of any notice from the Company of the happening of an event pursuant to Section 3(e) hereof, such Investor will immediately discontinue disposition of Registrable Securities pursuant to the Registration Statement covering such Registrable Securities, until the Investor is advised by the Company that such dispositions may again be made.

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5. Indemnification.

(a) Indemnification by the Company. The Company will indemnify and hold harmless each Investor and its officers, directors, members, employees and agents, successors and assigns, and each other person, if any, who controls such Investor within the meaning of the 1933 Act, against any losses, claims, damages or liabilities, joint or several, to which they may become subject under the 1933 Act or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon: (i) any untrue statement or alleged untrue statement or omission or alleged omission of any material fact contained in any Registration Statement, any preliminary Prospectus or final Prospectus, or any amendment or supplement thereto; (ii) any blue sky application or other document executed by the Company specifically for that purpose or based upon written information furnished by the Company filed in any state or other jurisdiction in order to qualify any or all of the Registrable Securities under the securities laws thereof (any such application, document or information herein called a “Blue Sky Application”); (iii) the omission or alleged omission to state in a Blue Sky Application a material fact required to be stated therein or necessary to make the statements therein not misleading; (iv) any violation by the Company or its agents of any rule or regulation promulgated under the 1933 Act applicable to the Company or its agents and relating to action or inaction required of the Company in connection with such registration; or (v) any failure to register or qualify the Registrable Securities included in any such Registration Statement in any state where the Company or its agents has affirmatively undertaken or agreed in writing that the Company will undertake such registration or qualification on an Investor’s behalf and will reimburse such Investor, and each such officer, director or member and each such controlling person for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, liability or action; provided, however, that the Company will not be liable in any such case if and to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement or omission or alleged omission so made in conformity with information furnished by such Investor or any such controlling person in writing specifically for use in such Registration Statement, Prospectus or Blue Sky Application.

(b) Indemnification by the Investors. Each Investor agrees, severally but not jointly, to indemnify and hold harmless, to the fullest extent permitted by law, the Company, its directors, officers, employees, shareholders and each person who controls the Company (within the meaning of the 1933 Act) against any losses, claims, damages, liabilities and expense (including reasonable attorney fees) resulting from any untrue statement or alleged untrue statement of a material fact or any omission or alleged omission of a material fact required to be stated in any Registration Statement, Prospectus or preliminary Prospectus, or amendment or supplement thereto, or any Blue Sky Application, or necessary to make the statements therein not misleading, to the extent, but only to the extent that such untrue statement or omission or alleged untrue statement or alleged omission is contained in any information furnished in writing by such Investor to the Company specifically for inclusion in such Registration Statement or Prospectus or amendment or supplement thereto or Blue Sky Application. In no event shall the liability of an Investor be greater in amount than the dollar

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amount of the proceeds (net of all expenses paid by such Investor in connection with any claim relating to this Section 5 and the amount of any damages such Investor has otherwise been required to pay by reason of such untrue statement or omission) received by such Investor upon the sale of the Registrable Securities included in the Registration Statement giving rise to such indemnification obligation.

(c) Conduct of Indemnification Proceedings. Any person entitled to indemnification hereunder shall (i) give prompt notice to the indemnifying party of any claim with respect to which it seeks indemnification and (ii) permit such indemnifying party to assume the defense of such claim with counsel reasonably satisfactory to the indemnified party; provided that any person entitled to indemnification hereunder shall have the right to employ separate counsel and to participate in the defense of such claim, but the fees and expenses of such counsel shall be at the expense of such person unless (A) the indemnifying party has agreed to pay such fees or expenses, or (B) the indemnifying party shall have failed to assume the defense of such claim and employ counsel reasonably satisfactory to such person or (C) in the reasonable judgment of any such person, based upon written advice of its counsel, a conflict of interest exists between such person and the indemnifying party with respect to such claims (in which case, if the person notifies the indemnifying party in writing that such person elects to employ separate counsel at the expense of the indemnifying party, the indemnifying party shall not have the right to assume the defense of such claim on behalf of such person); and provided, further, that the failure of any indemnified party to give notice as provided herein shall not relieve the indemnifying party of its obligations hereunder, except to the extent that such failure to give notice shall materially adversely affect the indemnifying party in the defense of any such claim or litigation. It is understood that the indemnifying party shall not, in connection with any proceeding in the same jurisdiction, be liable for fees or expenses of more than one separate firm of attorneys at any time for all such indemnified parties. No indemnifying party will, except with the consent of the indemnified party, consent to entry of any judgment or enter into any settlement that does not include as an unconditional term thereof the giving by the claimant or plaintiff to such indemnified party of a release from all liability in respect of such claim or litigation. Unless the indemnifying party has failed to assume the defense of a claim in accordance with the requirements of this Section 5, no indemnified party shall settle any action, claim or proceeding effected without the prior written consent of the indemnified party; provided, however, that the indemnifying party shall not unreasonably withhold its consent. Following indemnification as provided hereunder, the Company shall be subrogated to all rights of the indemnified parties with respect to all third parties, firms or corporations relating to the matter for which indemnification has been made.

(d) Contribution. If for any reason the indemnification provided for in the preceding paragraphs (a) and (b) is unavailable to an indemnified party or insufficient to hold it harmless, other than as expressly specified therein, then the indemnifying party shall contribute to the amount paid or payable by the indemnified party as a result of such loss, claim, damage or liability in such proportion as is appropriate to reflect the relative fault of the indemnified party and the indemnifying party, as well as any other relevant equitable considerations. No person guilty of fraudulent misrepresentation within the meaning of Section 11(f) of the 1933 Act shall be entitled to contribution from any person not guilty of such fraudulent misrepresentation. In no event shall the contribution obligation of a holder of Registrable Securities be greater in amount than the dollar amount of the proceeds (net of all expenses paid by such holder in connection

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with any claim relating to this Section 5 and the amount of any damages such holder has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission) received by it upon the sale of the Registrable Securities giving rise to such contribution obligation.

6. Miscellaneous.

(a) Amendments and Waivers. This Agreement may be amended only by a writing signed by the Company and the Required Investors. The Company may take any action herein prohibited, or omit to perform any act herein required to be performed by it, only if the Company shall have obtained the written consent to such amendment, action or omission to act, of the Required Investors.

(b) Notices. Notices. Unless otherwise provided, any notice required or permitted under this Agreement shall be given in writing and shall be deemed effectively given as hereinafter described (i) if given by personal delivery, then such notice shall be deemed given upon such delivery, (ii) if given by telecopier, then such notice shall be deemed given upon receipt of confirmation of complete transmittal, (iii) if given by mail, then such notice shall be deemed given upon the earlier of (A) receipt of such notice by the recipient or (B) three Business Days after such notice is deposited in first class mail, postage prepaid, and (iv) if given by an internationally recognized overnight air courier, then such notice shall be deemed given one Business Day after delivery to such carrier. All notices shall be addressed to the party to be notified at the address as follows, or at such other address as such party may designate by ten days’ advance written notice to the other party:

If to the Company:

c/o The W Group

655 Wheat Lane

Wood Dale, Illinois 60191

Attention: Chief Financial Officer

Fax: (630)  ###-###-####

With a copy to:

Katten Muchin Rosenman LLP

525 West Monroe Street

Chicago, Illinois 60661-3693

Attention: Mark D. Wood, Esq.

Fax: (312)  ###-###-####

If to any Investor:

to its address in the stock records of the Company.

(c) Assignments and Transfers by Investors. The provisions of this Agreement shall be binding upon and inure to the benefit of the Investors and their respective

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successors and assigns. An Investor may transfer or assign, in whole or from time to time in part, to one or more persons its rights hereunder in connection with the transfer of Registrable Securities by such Investor to such person, provided that such Investor complies with all laws applicable thereto and provides written notice of assignment to the Company promptly after such assignment is effected, which notice contains an agreement of such transferee to be bound by the provisions hereof.

(d) Assignments and Transfers by the Company. This Agreement may not be assigned by the Company (whether by operation of law or otherwise) without the prior written consent of the Required Investors; provided, however, that in the event that the Company is a party to a merger, consolidation, share exchange or similar business combination transaction in which the Common Stock is converted into the equity securities of another Person, from and after the effective time of such transaction, such Person shall, by virtue of such transaction, be deemed to have assumed the obligations of the Company hereunder, the term “Company” shall be deemed to refer to such Person and the term “Registrable Securities” shall be deemed to include the securities received by the Investors in connection with such transaction unless such securities are otherwise freely tradable by the Investors after giving effect to such transaction.

(e) Benefits of the Agreement. The terms and conditions of this Agreement shall inure to the benefit of and be binding upon the respective permitted successors and assigns of the parties. Nothing in this Agreement, express or implied, is intended to confer upon any party other than the parties hereto or their respective successors and assigns any rights, remedies, obligations, or liabilities under or by reason of this Agreement, except as expressly provided in this Agreement.

(f) Counterparts; Faxes. This Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. Any signature page to this Agreement may be delivered via facsimile or other form of electronic transmission, which signature page so delivered shall be deemed an original.

(g) Titles and Subtitles. The titles and subtitles used in this Agreement are used for convenience only and are not to be considered in construing or interpreting this Agreement.

(h) Severability. Any provision of this Agreement that is prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof but shall be interpreted as if it were written so as to be enforceable to the maximum extent permitted by applicable law, and any such prohibition or unenforceability in any jurisdiction shall not invalidate or render unenforceable such provision in any other jurisdiction. To the extent permitted by applicable law, the parties hereby waive any provision of law which renders any provisions hereof prohibited or unenforceable in any respect.

(i) Further Assurances. The parties shall execute and deliver all such further instruments and documents and take all such other actions as may reasonably be required to carry out the transactions contemplated hereby and to evidence the fulfillment of the agreements herein contained.

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(j) Entire Agreement. This Agreement is intended by the parties as a final expression of their agreement and intended to be a complete and exclusive statement of the agreement and understanding of the parties hereto in respect of the subject matter contained herein. This Agreement supersedes all prior agreements and understandings between the parties with respect to such subject matter.

(k) Governing Law; Consent to Jurisdiction; Waiver of Jury Trial. This Agreement shall be governed by, and construed in accordance with, the internal laws of the State of Illinois without regard to the choice of law principles thereof. Each of the parties hereto irrevocably submits to the exclusive jurisdiction of the courts of the State of Illinois located in Cook County and the United States District Court for the Northern District of Illinois for the purpose of any suit, action, proceeding or judgment relating to or arising out of this Agreement and the transactions contemplated hereby. Service of process in connection with any such suit, action or proceeding may be served on each party hereto anywhere in the world by the same methods as are specified for the giving of notices under this Agreement. Each of the parties hereto irrevocably consents to the jurisdiction of any such court in any such suit, action or proceeding and to the laying of venue in such court. Each party hereto irrevocably waives any objection to the laying of venue of any such suit, action or proceeding brought in such courts and irrevocably waives any claim that any such suit, action or proceeding brought in any such court has been brought in an inconvenient forum. EACH OF THE PARTIES HERETO WAIVES ANY RIGHT TO REQUEST A TRIAL BY JURY IN ANY LITIGATION WITH RESPECT TO THIS AGREEMENT AND REPRESENTS THAT COUNSEL HAS BEEN CONSULTED SPECIFICALLY AS TO THIS WAIVER.

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IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized officers to execute this Agreement as of the date first above written.

[Signature Page to Shareholder Registration Rights Agreement]