02-16-2006, 11:46 PM
Join Date: Dec 2004
What I Drive: 2004 EAP SEX
FF Reputation: 1
Buy-Sell-Trade Rating: (1
This is the reason we have a Hanging Idle on cold starts:
Even with this broader torque range and horsepower boost, the vehicle still is certified to the stringent standards of the National Low Emission Vehicle (NLEV) program and complies with California's Low Emission Vehicle (LEV) standard. In Europe, the engine is certified to Stage IV emissions standards.
To accomplish this, engineers had to find a way to reduce the light-off time of the vehicle's catalyst. Catalysts must heat up to work effectively, and this can sometimes take up to two minutes with most modern engines. The easiest way to accomplish this is to put the catalyst as close as possible to the engine, which is especially helpful when the engine is run from cold at low speeds. But while that achieves faster light up, it can rob precious amounts of horsepower and create large amounts of unwanted backpressure on the engine.
SVE and Cosworth Technology engineers had to find a way to shorten this heating up period or light-off time without a trade-off in performance, while at the same time delivering on strict emissions requirements. A tuned 4-2-1 tubular exhaust manifold coupled to an underbody catalyst was used to achieve the performance and emission targets. The calibration retards the spark during cold start, heating up the exhaust to facilitate faster converter light off to provide a clean exhaust.