What is the difference between a Porsche 911 and 911s?

I guess your talking about the 911S and 911L? Porsche basically introduced three letter designations in 1967-68 to name the different variants of the basic 911 they were introducing. They ranged from lowest to highest in power and luxury. The 911S was Porsche's "Sport" model 911 between 1967 and 1978. It had a more powerful engine than just the base 911 and included fancier trim, sporting the first Fuch alloys when it was introduced instead of the old 356 inspired wheels on the base 911. The "Sport" model was to receive the newest updates, including mechanical fuel injection, while the 911T was still stuck with a carburetor. The next step down was the 911L (it switched letters to 911E after a short time). It was basically a basic 911 model that sported the 911S trim, was a little less expensive than the 911S, and had a little more horsepower than the 911T, but a little less than the 911S. It was sandwhiched between these two models and was the middle of the road 911. The difference is that it was not as powerful as the S, and received new updates a little later than the S. That's about all I know. If your interested look it up.