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                                                                   EXHIBIT 10.41

         AMENDMENT NO. 4 TO AMENDED AND RESTATED BUSINESS LOAN AGREEMENT

This Amendment No. 4 to Amended and Restated Business Loan Agreement dated as of
December 12, 2001 (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 Technologies, Inc. (the "Subsidiary
Borrower").

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

     1. 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 terms are hereby amended and restated in
their entirety beginning on the effective dated of this Amendment as set forth
below:

         "Offshore Margin" means 4.00%.
          ---------------

         "Prime Rate Margin" means 2.25%.
          -----------------

         "Unused Commitment Fee Rate" means 0.35%.
          --------------------------


     2. Amendment to Section 1.2. Section 1.2 of the Loan Agreement is hereby
        ------------------------
amended by deleting the reference to "November 30, 2001" and substituting in
place thereof a reference to "January 31, 2002".

     3. 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, with the substituted
language set forth in bold and underscored text for the convenience of the
reader:

"(b) The Borrower will repay principal in three (3) successive quarterly
                                          ---------
installments of Six Hundred Thirty Five Thousand Three Hundred Six Dollars
($635,306) each commencing June 30, 2001. On January 31, 2002, the Borrower will
                                             ----------------
repay the remaining principal balance plus any interest then due."

     4. 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, with the substituted
language set forth in bold and underscored text for the convenience of the
reader:

     5. "(b) The Borrower will repay the principal amount outstanding on
Facility No. 3 in one installment, equal to $109,375.00, payable December 31,
                  -----------------------------------------------------------
2001. On January 31, 2002, the Borrower will repay the remaining principal
----     ----------------
balance plus any interest then due."

     6. Amendment to Section 5.1. Section 5.1 of the Loan Agreement is hereby
        ------------------------
amended to provide that, beginning on the effective date of this Amendment, the
interest rate payable with respect to prime rate loans under each of the
Facilities shall be the Prime Rate plus the Prime Rate Margin.

     7. 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
optional interest rate payable with respect to Portions under each of the
Facilities shall be the IBOR Rate or the LIBOR Rate plus the Offshore Margin.

     8. Amendment to Section 5.4(a). Section 5.4(a) of the Loan Agreement is
        ---------------------------
hereby amended and restated to read in full as follows, with the substituted
language set forth in bold and underscored text for the convenience of the
reader:

"(a) The interest period during which the IBOR Rate will be in effect will be no
                                                                              --
longer than 14 days. The last day of the interest period will be determined by
-------------------
the Bank using the practices of the offshore dollar inter-bank market."

     9. Amendment to Section 5.5(a). Section 5.5(a) of the Loan Agreement is
        ---------------------------
hereby amended and restated to read in full as follows, with the substituted
language set forth in bold and underscored text for the convenience of the
reader:

"(a) The interest period during which the LIBOR Rate will be in effect will be
no longer than 14 days. The first day of the interest period must be a day other
----------------------
than a Saturday or a Sunday on which the Bank is open for business in
California, New York and London and dealing in offshore dollars (a "LIBOR
Banking Day"). The last day of the interest period and the actual number of days
during the interest period will be determined by the Bank using the practices of
the London inter-bank market."

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     10. Amendment to Section 11.3. Section 11.3 of the Loan Agreement is hereby
         -------------------------
amended and restated to read in full as follows, commencing with the quarterly
period beginning August 1, 2001:

"[[[Intentionally Omitted]]]"

     11. Amendment to Section 11.4. Section 11.4 of the Loan Agreement is hereby
         -------------------------
amended and restated to read in full as follows, commencing with the quarterly
period beginning August 1, 2001:

         "[[[Intentionally Omitted]]]"

     12. Interim Increase in Availability.
         --------------------------------

         a.   It is acknowledged that as of the date hereof, the Borrower has
              consented to a reserve against the lending commitments of Lender
              in the amount of $2,500,000 until such time as the Borrower has
              demonstrated to the satisfaction of Bank that cash and cash
              equivalents in the amount of the required liquidity reserve
              required by Section 11.7(k) of the Loan Agreement are in its
              possession. During the period beginning on the effective date of
              this Amendment and ending on January 31, 2002, the Borrower and
              the Subsidiary Borrower may borrow under Facility No. 1
              additional funds of up to $1,500,000 of such reserve, or up to a
              total maximum of $14,000,000, to the extent that the Borrower and
              the Subsidiary Borrower have filed tax refund requests as set
              forth below.

         b.   The Borrower and the Subsidiary Borrower may obtain advances
              hereunder upon providing the Bank with copies of filed state or
              federal tax returns confirming the amount of the anticipated tax
              refund. The aggregate amount of advances made hereunder shall not
              exceed the aggregate refund amounts requested in tax returns
              provided to the Bank.

         c.   Advances made hereunder shall be repaid upon receipt by the
              Borrower or the Subsidiary Borrower of the applicable tax refund
              relating to such advances. Once repaid, amounts borrowed
              hereunder may not be reborrowed.

         d.   Each advance hereunder shall bear interest at the rates provided
              in Section 5 of the Loan Agreement for loans under Facility No.
              1.

     13. 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.   An amendment fee paid by the Borrower to the Bank in an amount
               equal to $50,000; and

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

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

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

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16.      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: W. Brian Olson
                               ----------------------------------

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


                            QUANTUM TECHNOLOGIES, INC.


                            By:  Syed Hussain
                               ----------------------------------

                            Title:  CEO
                                  -------------------------------


                            BANK OF AMERICA, N.A.


                            By:  Jeff Thom
                               ----------------------------------

                            Title:  VP
                                  -------------------------------

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