Yes, you can adjust the length of the rod. To do this, you go from underneath the car. If you slide your head up under about where the oil fiter is, you can look up and see the bottom of your turbo charger. You will also see a rod there that is fastened with safetywire to something going into the turbo. The rod has a locking nut on the same end. Undo the safety wire, and simply shorten the rod. This will increase the boost. The rule of thumb I heard was about two turns per psi of boost change. Lengthening will increase the boost.

Once you have made the change, go for a test drive. get the car in second gear at about 4000 rpm and floor it. If you here pinging, knocking, or hit the fuel cut off, lengthen the rod a little until it goes away. The adjustment may take an afternoon by the time you go through adjusting, warming the engine up, testing, letting stuff get cool enough to touch, then re-adjusting, etc.

BTW: The fuel cut off is the last line of deffense for the engine. Basically, Volvo put it in there so that if something went wrong with the wastegate, the engine will not be harmed.

To be really safe, you should check your plugs and get some idea how hot the motor is burning. You may be running too lean, not knocking and not pinging, but still burning exhaust valves.

So, how much boost can you run? If you modify the fuel system to deliver extra fuel at extreme boost, and you add water cooling, you can probably run about 25 to 30 psi of boost and put out somewhere on the order of 350 bhp. The motor will be reasonably reliable (good for 10 to 20k miles) before you have to rebuild it.

BUT! you will probably leave most of your driveline in a scrap yard before the engine blows. If you have a volvo turbo with a manual gear box, be careful about increasing the boost. You will really strain the clutch. You also run the chance of blowing up your transmition. The volvo turbos got alloy manual gear boxes. They tend not to put up with a lot of power being pumped through them in first or second gear. (The Homologated turbos ran homologated Getrag 5 speed racing gear boxes.)

Automatics tend to fair a bit better, but remeber, you are still putting a lot more stress on the whole driveline, including the u-joints and differential.