Is there a way to add a turbocharger to a stock 93 850?
It would be easier to drop in a turbocharged engine from a turbo model of the same or close year. I don't think there is any economical way to do what you are asking to the stock model.
Honestly In my opinion it would cost you alot more to add all of the necessary parts to make it a turbo. It would add up very fast and you could purchase a used 850 turbo for anywhere $2500 - 4000. You can easily do it to an older "Red Block" motor the volvo's up until the 850 model came out due to them being cast iron engines, whereas the new "Whiteblock" 850 engines are completely aluminum which does not allow really for much room for advancement on the GLT motors (2.4 L). If you would like more information, http://forums.turbobricks.com/showthread.php?t=52466 it has alot about older volvo's (Redblocks) but it should still have some information on the newer style 850 motor's (Whiteblocks)
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