Why do you suggest this for turbos only?

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

It will work with the 300D NA (I have one in my car). However, it's most or more noticable in the turbo. So, I guess I should have been a smidge more clear. My bad. In other words, it will work in your car also. I popped mine in about a month ago and it was noticable -- even for a 300D NA. I am targeting the turbo folks and mod'd turbo folks since it's a really nice upgrade.