Quote:
MECHANICAL COMPONENTS
CYLINDER HEAD AND PISTONS
(Canada models only)
For improved fuel consumption, the combustion chamber has been changed from an open-type to a newly designed wedge shaped type. The intake port has also been changed to a low port type in order to improve fuel consumption by increasing the swirl effect. In conjuction with this combustion chamber modification, the piston has also been changed. That is to say, the concavity of the top land has been increased to maintain a certain compression ratio. The cylinder head and pistons are the same as those used in the 1977 U.S.A. B210 GFU model.
1977: Open chamber, Oval Port, 4mm dish
1978: Closed chamber, Round Port, 5mm dish