accelerations). These catalysts apparently have about 60 percent NOX conversion efficiency on the
Japanese test cycle, and represent practical solutions that are already commercially available.
Toyota did not believe that this type of catalyst is suitable for U.S. conditions, as it is easily
poisoned by fuel sulfur, which is very low in Japan but high in the United States. Nevertheless,
such a solution is available if EPA requires reformulated gasoline to meet new sulfur
specifications of 10 ppm, equivalent to the sulfur content of Japanese gasoline.The Mazda catalyst is a “lean-NOx” zeolite catalyst with platinum, rhodium and iridium as the
noble catalytic materials. The catalyst is used on the Protege model and has a volume of 1.7 liters,
as compared with 0.5 liters for the conventional catalyst on the nonlean bum Japanese model.
Mazda claims a NOX reduction efficiency of over 50 percent in the lean regime.^56Price Effects of Engine Improvements and Advanced Engines.
Many of the potential improvements to piston engines, both gasoline and diesel, have been
introduced commercially in a few models in Europe and Japan. In cases where these technologies
are available in mass-market cars, and available from more than one manufacturer, the option
price should reflect the true RPE effect on average.Four-valve engines are already widely available, with an average price differential of$110 to
$120 relative to an overhead cam (OHC) four-cylinder two-valve engine of equal performance,
not equal displacement.^57 A two-stage variable resonance manifold was estimated at $30 to 35
relative to a one-stage manifold.The RPE for the two-position Variable Valve Lift and Timing (VVLT) system by Honda is
estimated from several available models at $250 to $300 for a four-cylinder engine. These
comparisons are based on the “adjusted” RPE for an equal power engine. The actual price
increment is higher for many models because the VVLT system improves horsepower by 15
percent and torque by 7 to 8 percent (at low rpm). The Mitsubishi MIVEC V-6 with both VVLT
and valve shutoff has an adjusted RPE in Japan of about $700 to $750, but Japanese prices are
higher owing to higher taxes than in the United States, and an equivalent U.S. RPE maybe in the
$530 to $600 range, for a V-6. Prices for a four-cylinder should scale approximately as the ratio
of number of cylinders, although an in-line six-cylinder engine could have lower costs for VVLT
and valve deactivation.Lean-bum engines have also been recently commercialized in Japan by Mitsubishi, Honda, and
Mazda. For each of these cases, there are comparable “three-way catalyst” equipped models, and
the RPE for lean-bum varies from $300 to $360 (calculated at 110 yen to the dollar). It appears
that about half the price increase is associated with the lean-bum catalyst. These costs could
decline with the “learning curve” effect and the RPE decrease to about $250 in the future.