Don't even think about it!
Lies, Lies, Lies. Advancing the timing on your NSX is free, will not produce 20HP, and can be done buy a good tech. Best of all... it's easily reversable in the same five minutes it takes to advance it.
I have this done on my NSX and it feels more responsiveness and smoother.
Be sure to run only the best fuel at all times, especially after doing this.
If you're going to buy a chip, get something like the Dali chip.
[This message has been edited by ilya (edited 18 March 2002).]