Friend of mine has a chipped GTi 1.8T, he swears by 112oct. But, when you say you are chipped, do you mean you have the "race" program? If you are not sure, you may want to speak with the shop that set you up with the software. Normally, if you do have high-octane setting, you can run 112 or 110 all day long. But, then, there is always the question of how many days in a row, right?
Sunoco sells a 104 octane unleaded fuel that you can safely run in all modern cars. It is kind of pointless to run though unless you have software to modify the ignition timing on the car to take advantage of the higher octane. You might be able to get small gains from it in extremely hot weather to prevent detonation and to keep the car from pulling timing, however a set of colder spark plugs like Autolite 3922's will do the same thing for way less $$$.
You can run leaded fuel safely, however w/ cars that have a cat you risk damaging the 02 sensors which aren't cheap to replace. Remove the cat and replace w/ a strait test pipe w/o 02 sensor bungs, and you will not have this problem.
With any luck, I will be running APR's V-Tune software in the next month, and with that you can adjust timing yourself. I will be replacing my cat w/ a test pipe and then playing with some C16 (117 - 118 octane) at the track to see how much timing advance I can get safely.....should be able to get a good bit. This stuff is really popular with the DSM and Supra guys......and the timing advance and increased boost they can run on it often shows huge gains.....I will not be adding boost though, simply more timing.
[ February 11, 2004: Message edited by: Big Dong ]