; and (2) fuel economy testing and calculation procedures under section 32904(c) of title 49, United States Code, the fuel economy of motor vehicles using the test fuels described in subsection (a) or (b) shall be determined on an energy-equivalent basis, which shall be equal to the product obtained by multiplying— (A) the measured fuel economy; and (B) the quotient obtained by dividing— (i) 114,086 British thermal units per gallon; by (ii) the volumetric energy density of the test fuel. 263. High-octane vehicles (a) Warranty requirements Manufacturers of motor vehicles described in section 261(b) shall warrant to the ultimate purchaser and each subsequent purchaser that each such motor vehicle is designed— (1) for model years 2028 through 2032— (A) to operate with gasoline containing 10 and up to and including 25 percent ethanol by volume; and (B) to meet the design requirements under subsection (b)(1); and (2) for model year 2033 and later model years— (A) to operate with gasoline containing 10 and up to and including 30 percent ethanol by volume; and (B) to meet the design requirements under subsections (b)(1) and (c)(1). (b) Design requirements before model year 2033 (1) Manufacturers The manufacturer of a motor vehicle described in section 261(b) shall design each such motor vehicle— (A) to use gasoline with a 95 research octane number or higher; and (B) to incorporate such devices or elements of design (including physical or other barriers, devices, or technological systems) as are determined by the Administrator to be— (i) necessary to prevent the introduction of gasoline with a research octane number that is lower than 95 into that motor vehicle