924Board.org

[ricomartinez]

Gotta comment again. Like you have said, displacement is figured by calculating bore x stroke x number of cylinders. Do a search on "engine displacement" and all the sites will say this. Read any book on the subject, and it will say the same. It is simply the volume that a piston displaces. Nowhere is combustion chamber volume (CCV) or compression ratio (CR) an issue.

Question: If CCV or CR affects displacement, does a 1978 924 at 8.5 CR have less displacement than a 1981 at 9.0 CR? No. They both displace 1984 CC's.

How about a little more abstract thinking. Someone said that if the CCV gets smaller, the displacement decreases. Well, if we make the CCV zero, is the displacement now zero? How about if we make the CCV infinite, does that make the displacement infinite? No. The piston still "displaces" a given volume.

Now, yes, you might have to add more fuel if you increase only CR. But there is something else at work other than a change in displacement.
Some possibilities:
-Maybe the CR change improved the piston's ability to pull in the intake charge thereby requiring more fuel.
-If you remember your gas laws, cramming the intake charge into a smaller volume will create more heat. More fuel might be required to prevent detonation or burning a piston.

There might be many more variables at work here...