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.