It increases the swept volume (capacity of your engine) by lengthening the distance the piston travels in the bore - its done by a modified crankshaft with a different set of pistons.
Gives you more torque, and more capacity to spin the massive turbo up.
man, I cannot WAIT until I get my car properly mapped and I am making that kind of power
When are you next on the dyno?
Ive been reading your buildup posts for ages and the car is looking awesome.
Do you have any other problems to fix or are you ready to get it tuned up now