It'll advance or retard the cam timing, which will affect mechanical timing as well as the ignition. If you want to advance ignition timing, just turn the distributor and watch the timing marks with a light. Remember to disconnect the SPOUT jumper (gray or black block by the TFI module). If you don't, the ECU will control the spark timing, and that won't look right when you're trying to tweak it. DO NOT move the timing belt by one tooth on the cam: that's equivalent to 12 degrees of mechanical time, and your engine will run like it's missing a cylinder. I personally run 12 degrees BTDC on the ignition timing. Stock is 8. I also run premium gas, so don't be messing with the timing much unless you want to stick better fuel in.