Would I have engine damage if I turbo charge a Volvo 240 with a b230fx engine ??
my mechanic says that the compression ratio is too high for a turbo

 

not familiar with B230FX, just B230F, FT(turbo).

your best bet would be to get a complete engine and harness and ECU/ICU and everything from a late model 940 turbo. the 94/95's have oil squirters inside the block to cool the piston skirts. the B230FT has lowered compression ratio, higher flow injectors, higher flow fuel pumps. the intercooler may be a tough fit in a 240, I dunno, 1992+ 940's got a bigger radiator and went all electric fans. lots of stuff changes with a turbo, the battery is relocated to the left side, the air cleaner is on the right side. there's additional coolant and oil plumbing to lubricate/cool the turbo. the oil cooler is relocated because the turbo is in the way of the side-of-block normal location. turbos have an AW71 automatic instead of the AW70, the '71 is beefier to handle the additional torque... or if they are stick shifts, they are M46 4 speed + overdrive, rather than M47 5-speed, same thing, M46 is sturdier.