<PAGE>

                                                                   Exhibit 10.49


              AMENDMENT NO. 8 TO AMENDED AND RESTATED BUSINESS LOAN
                                    AGREEMENT

           This Amendment No. 8 to Amended and Restated Business Loan Agreement
dated as of March 31, 2002 (this "Amendment") is executed with reference to the
Amended and Restated Business Loan Agreement dated as of April 30, 2001 (as
amended, the "Loan Agreement") among Bank of America, N.A. (the "Bank"), IMPCO
Technologies, Inc. (the "Borrower") and Quantum Fuel Systems Technologies
Worldwide, Inc. (under its former name, Quantum Technologies, Inc.) (the
"Subsidiary Borrower").

           The parties hereby agree to amend the Loan Agreement as follows:

           Defined Terms. All initially capitalized terms used in this Amendment
without definition shall have the respective meanings assigned thereto in the
Loan Agreement. The following defined term is hereby amended and restated in its
entirety beginning on the effective date of this Amendment as set forth below:

           "Offshore Margin" means 5.00%.

           New Defined Term. The Loan Agreement is hereby amended to add the
following new defined term:

           "Swap Agreement" means the ISDA Master Agreement dated as of December
2, 1996, between Borrower and the Bank (under its former name, Bank of America
National Trust and Savings Association), as at any time amended.

           Amendment to Section 1.1(a). Section 1.1(a) of the Loan Agreement is
hereby amended to read in full as follows:

           "(a) During the availability period described below, the Bank will
provide a line of credit ("Facility No. 1") to the Borrower. The amount of the
line of credit (the "Facility No. 1 Commitment") is Nine Million Five Hundred
Thousand Dollars ($9,500,000)."

           Amendment to Section 1.2. Section 1.2 of the Loan Agreement is hereby
amended by deleting the reference to "March 31, 2002" and substituting in place
thereof a reference to "May 31, 2002".

           Amendment to Section 2.3(b). Section 2.3(b) of the Loan Agreement is
hereby amended and restated to read in full as follows:

           "(b) The Borrower will repay principal in one installment of Six
Hundred Thirty-Five Thousand Three Hundred Six Dollars ($635,306) payable March
31, 2002. On May 31, 2002, the Borrower will repay the remaining principal
balance plus any interest then due."

                                      - 1 -

<PAGE>

           Amendment to Section 3.4(b). Section 3.4(b) of the Loan Agreement is
hereby amended and restated to read in full as follows:

           "(b) The Borrower will repay the principal amount outstanding on
Facility No. 3 in one installment, equal to One Hundred Twenty-Five Thousand
Dollars ($125,000) payable March 31, 2002. On May 31, 2002, the Borrower will
repay the remaining principal balance plus any interest then due."

           Amendment to Section 5.2. Section 5.2 of the Loan Agreement is hereby
amended to provide that, beginning on the effective date of this Amendment, the
Borrower may only elect the optional interest rate with respect to Facility No.
2. The optional interest rate payable with respect to Portions under Facility
No. 2 shall be the LIBOR Rate plus the Offshore Margin.

           Obligations Secured By Security Agreements. Borrower and Subsidiary
Borrower hereby agree that the obligations secured by the security agreements
previously executed by each of them in favor of the Bank shall include any and
all obligations under the Swap Agreement, as defined herein.

           Cash Reserve. Borrower hereby agrees that it shall at all times
segregate and maintain a cash reserve in the amount of Two Million Dollars
($2,000,000).

           Investments in Subsidiary Borrower. Borrower's aggregate investments
in Subsidiary Borrower following the date hereof through the earlier of (i) May
31, 2002 or (ii) the Quantum Spin-off Date, shall not exceed Three Million
Dollars ($3,000,000).

           Conditions Precedent. The effectiveness of this Amendment shall be
conditioned upon receipt by the Bank of all of the following:

           a.  Counterparts of this Amendment executed by all parties hereto;

           b.  Receipt by the Bank of the amounts due and owing under Facility
               No. 2 and Facility No. 3 as of March 31, 2002, pursuant to
               Sections 2.3(b) and 3.4(b), as amended hereby;

           c.  Receipt by the Bank of an amendment fee in the amount of $15,000
               and payment of the Bank's legal fees and expenses of its counsel,
               including any outstanding invoices; and

           d.  Such other assurances, certificates, documents, consents or
               opinions as the Bank reasonably may require.

           Representations and Warranties. The Borrower hereby represents and
warrants that no default under Section 13 of the Loan Agreement has occurred and
remains continuing.

           Counterparts. This Amendment may be executed in counterparts in
accordance with Section 14.12 of the Loan Agreement.

                                      - 2 -

<PAGE>

           Confirmation.  In all other respects, the Loan Agreement is
confirmed.

           IN WITNESS WHEREOF, the parties hereto have executed this Amendment
as of the date first written above by their duly authorized representatives.

                                       IMPCO TECHNOLOGIES, INC.


                                       By: /s/ W. Brian Olson
                                           ------------------

                                       Title:  CFO
                                             ------------


                                       QUANTUM FUEL SYSTEMS
                                       TECHNOLOGIES WORLDWIDE, INC.
                                       (formerly known as Quantum Technologies,
                                       Inc.)


                                       By: /s/ Alan Niedzwiecki
                                           --------------------

                                       Title:  President
                                               ---------


                                       BANK OF AMERICA, N.A.


                                       By: /s/ David P. Maiorella
                                           ----------------------
                                       David P. Maiorella, Vice President

                                      - 3 -