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You are begging for trouble with this one. Here is the deal: the engine and fuel systems are designed with a specific pressure in mind, that is to keep the mixture around say 13.8:1 under full power. Say the fuel pressure is 45PSI at this point under 10PSI boost. Now add another 5PSI to that and your fuel pressure is now down to 40PSI because of the pressure head on the business ends of the injectors. Your mixture may slide to say 14.5:1 and Exaust Gas Temps will rise another 30%. Now lets look at it from the end of the piston and rods. Lets say at 10 pounds the mean combustion pressures are 200 PSI with a spike at 600 pounds, add another 5 pounds and lean the mixture out a little you now have maybe 250 pounds mean pressure with a spike at say 850 pounds.
Moral of the story is an increase in air pressure to the cylinder is not always going to allow the fuel system to follow with this increase and the HP gain between 10 pounds and 15 pounds is not going to be substantial, in the case of the volvo electronic (bosch) system this holds true. There is not enough latitude in the regulator to allow this and the electronics are not going to allow and additional period of injector open time to stretch the fuel injection cycle. What will happen and I can speak from experience is your engine may handle it for a short period of time however repeated trauma of unheard detonation and additional heat will take its toll starting with the rings. When they begin to fail they will allow oil into the cylinder by "wicking" action and as the piston rises for the fire it will have an oily crown. Fire the mixture that is already hot and you end up with even more detonation. Nothing kills the octane rating faster than lube oil because it has an affinity to burn under elevated pressures. That additional spike in pressure will hammer out the rod bearings, ring the crank into a harmonic and at the least blow out the head gasket if you're lucky.
I went through this with a 740 turbo that had 54k miles on it. Ran great but I got greedy with both shift points and boost, changed the wastegate to a 20 PSI diesel model from a Cummins set and plugged the overboard dump. Went like a raped ape and very little could keep up with me when I started swimming at 4000. At the time I had no idea what was going on until it was explained to me in detail by my dad who is a mechanical engineer. For every 1 PSI head you increase the base inlet temp by 15 degrees over the inlet and another 75 degrees on the exaust side. How does 2300F sound going down the exaust pipe? This was explained to me during the ride home when my motor blew up during normal highway driving, no boost at that point.
Recommended reading on this is a book called "Turbochargers" written by Hugh MacInnes. This has been long considered the bible of turbocharged engines and applications and even goes into a little detail of a turbocharged volvo setup by Janspeed.
Any engine can be turbocharged beyond its thermal and mechanical limits.
Good Luck
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