A quick review of the BMW Performance Intake. For install instructions, please see the DIY section. Seriously, it is simple, but there is one step that you need to see the DIY to make it work correctly.
Specifically to a ZHP, this intake adds a small amount of sound. It really took about 2 days to notice the difference. I don't know if that is because the Computer changed something once it registered the extra airflow, or it was just me. I like the added sound. Also, appearance in the engine bay is an added plus. As far as performance, i did not notice a difference. There may be some improved throttle response, but again, negligible. I noticed a major improvement in gas mileage for the first 3 tanks. About 2 mpgs. I do almost exclusive city driving, and so about 300 miles per week. I calculate my mileage every fill up, and am not relying on the cpu. After the first 3 fill ups, mileage has lowered again, but is still up about 1 mpg. This may also be due to CPU adjusting for the extra air. I am not smart enough to know for sure.

All in all, i am happy with the intake, and would recommend it to those looking for the items noted above. If you are installing it to increase HP, it might not be the best place to spend your money.