Rated at between 21/28 (2.5l, manual) and 27/34 (2.0l, auto), the Nissan Sentra is a fairly efficient car, albeit rapidly falling out of contention with its new 40 MPG competitors. Using a computer simulation, the developers of the “split-cycle” Scuderi engine showed that their unique, downsized, turbocharged engine can improve up to a 35% improvement in a “stock” Sentra’s fuel economy, when paired with the firm’s AirHybrid system. It’s not clear, even after listening to a podcast with VP Steven Scuderi, which engine-transmission combination was simulated as the “stock” baseline, but for practical purposes the best-performing Scuderi engine (tuned to match the “stock” engine’s power) achieved between 40 MPG and 32 MPG combined (around 50 MPG CAFE combined, or approaching the 2025 standard). Or, not. The EPA city test reportedly does not show improvements with idle fuel shutoff (stop-start), but Scuderi’s simulated stop-start system shows a 14% improvement over the non-start-stop “stock” Sentra on the same FTP-75 test. Was Mazda bluffing (it’s since said it would bring stop-start to all its cars), or is Scuderi’s simulation off? Scuderi (which has nondisclosure agreements with 11 OEMs and is in discussions with 4-5 more) says it will release more information next week at the Engine Expo 2011 in Stuttgart, Germany.