Ive got a turbo grand am and I was wondering what the bennifits of advancing or retarding the ignition timing would be

Advancing the timing generally increases chamber heat and can cause more negative work to be performed on the pistons. Retarding timing generally increases exhaust heat and decreases pressure generated on the piston. Turbo cars are a balance between increasing the timing for more efficiency and decreasing the timing to generate more heat to power the turbo. I've found that GM's timing for the 2.0 OHC engine is a bit agressive if you want to run increased boost. My manual trans equipped 'bird had so much timing at light load and low throttle angles that it would often buck violently.

-->Slow

so if I wanted to increase boost a bit should I retard it a bit

Yes, but the place to do it is in the chip, not at the distributor. Turning timing down at the distributor affects all the timing, which isn't so good for mileage or non-boost power.

-->Slow

ok what do I have to do to reach 250 275 hp