There are two things for fitment. The header portion that bolts to the block and then the back portion to the exhaust. I know there are customers that purchase these headers to put on the E60 525 (non turbo) models because the block in the same. Then they add a couple of inches to the back end so that it connects to the exhaust. You can imagine it is easier to extend a couple of inches in straight pipe than to do the primaries from the scratch. In your case of the Z4, although the head may be the same, the exhaust portion may not. And until I can test and confirm this personally I will not sell it as such.
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Andy
- trader-nas