whats the bolt nut size for the turbo on a 1987 740?

 

Well, which bolt or nut do you mean (there are several), and is your turbo Garrett or Mitsubishi?

 

the parts diagrams I have just list the bolts and nuts by the volvo part number, no clue on the size. I imagine the exhaust side has to be good high temperature steel

this is a 1991 940 garret:
Turbocharger with connecting parts B230FT/GT garrett B230FT 1990- garrett B230FT/GT garret 1990- B230FT garret 1990- B230FT, B230GT garret 1990 garrett B230GT/FT. Fits: 1991 Volvo 940 2.3l Fuel Injected Turbo | VolvoPartsWebstore.com

and 91 mitsubishi
Turbocharger with connecting parts mitsubishi B200FT mitsubishi B230FT mitsubishi 1990- B230FT, B230GT mitsubishi 1990 B230FT 1990- mitsubishi TURBO mitsubishi. Fits: 1991 Volvo 940 2.3l Fuel Injected Turbo | VolvoPartsWebstore.com

there's other diagrams showing the exploded view of the turbos.