I am going to swap out an 85 in the place of my 81 turbo on the 300SD but noticed a few minor differences. The 85 has what looks like a vacuum fitting on the front of the unit. Can this just be plugged or does it even need that?

Is there any other difference that one might need to be aware of? I know it is in a slightly differnt case so the air cleaner and connecting pipe will need to be changed also.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

I think there are some good threads on this... perhaps in those which were talking about rebuilding a turbo... maybe search for " waco"...
81-84 mostly the same , 85 different....The sticky on vacuum diagrams may help also....

Seem to have changed. I tried adding some boolean logic e.g. AND but the search did not modify the results.
There are just tooo many threads when you do a straight search for turbo...

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

I have an 85 300 SD. I think you are referring to the Air recirculation valve on the front of the turbo. The ARV and the EGR have small vacuum lines running to both for emission purposes. Both according to several threads can be bypassed.