The extra 25 horsepower comes from additional lift and duration on the intake camshaft, and the necessary fuel mapping programming differences to accompany it. That's it. All other equipment on the engine is exactly the same. Early Northstars (like 1993-1995 engines) had stiffer valve springs on the Touring models, but starting in 1996-1997, all Northstars were equipped with the stiffer springs, so that difference went away.
Increased performance is due to the extra horsepower and the shorter gearing (the Touring models have 3.71:1 final gearing and the "base" models have 3.11:1 final gearing).
Well, the question was where does the HP come from. That comes from the camshaft differences and the necessary programming. Assuming he may have also been asking why the Touring models are faster, I wanted to mention the differences in gearing, because they all play a part in the final outcome.
Since this is such a popular topic, would someone care to write up a small article for me to post up on the site? It doesn't need to be just one person, either.. I'd just like something set for easy reference.. Maybe even for a "most frequently asked questions" forum...