There are three levels each for Stage 1 and Stage 2. Stage 1 can get you up to 63 additional ponies and 70 lb.-ft. of additional twist, while Stage 2 can boost the numbers by 70 and 90 respectively. The AccessPort can also save your stock ECU data and reflash it when you decide you're finished with all that extra gumption. According to a GT-R owner who tried it out, you can be blowing past all those regular GT-Rs in less than an hour.
And that's not all: you can store multiple engine mapping programs, remove trouble codes, install reduced-power valet and economy modes, and update maps over the Internet. It seems like a ridiculously easy proposition for making your supercar that much more super. So if you got one of those GT-Rs that are a little low on horses, this could be just the ticket.
[Source: Bespoke Ventures]