Originally Posted by motoguy128
The changes made to the pwoertrain ot attain ULEV and SULEV are mostly related to cost than specifically engine performance. A manufacturer might use a more expensive O2 sensor or multiple sensors to achieve tighter control o nteh air/fuel ratio. The second change is a more expensive and/or complex catalytic converter. Some Cat's cost more because they contain more of one or another perticular metal catalyst and may have a more restrictive design to achieve more complete conversion of certain emissions.
TO control manufacturing costs, I wouldn't expect there to be any mechanical changes to the VTEC. Only small changes to the fuel mapping or program.
You are correct sir. The SULEV has a much cleaner cat and has a special 'A/F Ratio Sensor' mounted in the front of the header as opposed to the regular O2 sensor mounted in the side of the head on ULEV models.
VTEC really has nothing to do with it.