Porting & polishing are much less of an issue in a turbocharged application since the intake tract is pressurized.

On a gasoline engine, where the intake tract is under vacuum, any reduction to airflow resistance is most helpful.

I am not saying porting & polishing gives no benefit, but don't expect it to make your 300SD run like a 560SEL.

Just keep the modifications and their benefits in the correct perspective...Bert