[racer]

I think its different shapped piston domes. I know on the 2.0l motors, the difference in compression is a function of the flat domed (euro) piston vs the american ones that have a recess on the top.

it would make sense that the US (California) spec cars used different motors to meet more stringent emission needs. Lower compression was a good start.

http://www.pelicanparts.com/914/914QA/914Q_euro_vs_usa.htm
http://www.pelicanparts.com/catalog/shopcart/9144/POR_9144_ENGpis_pg1.htm#item2

I thought the "thing/181" didn't use a type IV motor..