I just bought a 81 300D with a frozen motor (sellers statement) is it desirable to replace this non turbo with a newer turbo model?

Yes, more power is always good.

Depends on how much work you want to do. I don't think it's a real hard swap, but others can fill you in better than I.

This is a sedan? Where do you live? Put it in your profile, and maybe someone who lives close would be willing to help out.

__________________
1979 240D, 4spd manual, Power Sunroof, manual windows, 147k miles, Pastel gray/Black MB Tex.
1991 300D 2.5 - Smokes like it's on Crack!

The transmission would need to be swapped as well....as the non-turbo trans is not intended to handle an extra 40+hp.....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Just find a shift kit that will adjust the VB to add more line pressure that will create more grip on the clutch disks. It might be risky on an old unit with poor maintenance but on a healthy trans a shift kit should be OK.

There has to be some simple modification to the trans to support the extra 40hp. I heard someplace that the non turbos get better fuel mileage. I can't see that but I'm new also.

__________________
Mad_Matt's Current Stable:
Oil Burners:
09 Jetta TDI The highway queen @ 105k
83 300D. Sold
Gassers:
16 A4 sport line
10 Passat
83 Recaro Trans AM WS6 Bone Stock Survivor
11 Harley Ultra

not to mention that the non-turbo models don't have a vacuum modulator while i believe the turbo models, or models after a certain indent year did have it

yes stock 240d's get better mileage than stock turbo w123's

Turbo 300d's are the most fuel efficient of the W123's.

Some 1981 W123's had a one-year-only trans that used vacuum controls but no bowden cable. I believe these transmissions start out in second gear as the older ones with the control rod do.(pre '80?)

I would think it better to stay with the transmission matched to whatever engine you decide to install.

If you install a turbo engine, remember to get the exhaust off the donor car , it is different.

With a turbo, you will probably want to go to the 3.07 or 2.88 rear diff also.

Dont forget to get the speedometer out of the donor car to match the rear diff. ratio