Quote:
Originally Posted by noro
Before this post gets too carried away with an insane volume of misinformation let me just state a few simple facts.
The key differences between the two engines is the PISTON. While it's true that the bore and stroke of the engines is the same and the actual displacement (as in the diameter of the combustion chamber multiplied by its length) is the same. The amount of the fuel the engine will take in during piston extraction and the amount of the compress you will get during piston's travel back depends (among many parts) on the piston head itself (as in the top shape / and overall height).
So, the only way to make 320i = 328i, is to replace the pistons.
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In November last year, a technical training session on N20 engine was offered to selective customers by a BMW dealer in Beijing, China. During the session the BMW trainer basically confirmed that the top shape of the piston head is different in 20i and 28i models. This is consistent with what one would logically derive from the compression ratio formula - reduced clearance volume resulting in higher compression ratio (11: 1 as in the case of 20i).
Unfortunately the post in the hyperlink below is in Chinese. However I think the pics might still be interesting to have a look at. In addition to an N20 engine torn apart, one gets to see many of the key components in this engine, as well as a few close-up shots of the pistons.
http://club.autohome.com.cn/bbs/thre...7972169-1.html