[Chrysler kid]

Well in my insomnia fueled learning binge I still have questions

Do only VTEC models run on 12 valves then switch to 16 valve operation under high throttle? I would think there would be more of a difference in mileage without VTEC if that was the case

Lean burn refers to the way the head is designed to let air ignite with fuel directly at the plug. Technically the car is always using the lean burn intake valve design but only restricts fuel during ideal conditions. It sounds like a very early form of direct injection which would explain why the cars are still viable today

No answer on egr valves however I believe it has to do with the lean burn and emissions. The intake manifold design cause the car to always run slightly lean and to meet emissions standards they included that on US lean burn models.

The d15b sounded Like it was the completion of the primary engineers design. He began working on it in 1988 to build it in the 1.5 and after all the logging for fuel maps was able to run the d15b on a 4 wire 02 sensor with ore programmed throttle settings stored in the ecm where as the 1.6 needed the 5 wire to program settings on the go.

My assumption is that Honda killed the 1.5 motor and the cost to develop the 1.6 into a 3 stage VTEC was too great to adapt to the large us market as it was mentioned several times the project was nearly killed before nearing completion in 1991