The Harley Davidson Sportster is a popular choice among Harley Davidson fans. You can get an 883 Sportster or a 1200 Sportster. The only difference between the 883 and 1200 Sportster is their emblems that indicate which model they are. The 883 and 1200 Sportster are actually built with the same exact parts and there is no way you can tell just by looking if a model is an 883 or a 1200 aside from the emblem.
The only difference between the 883 and 1200 Sportster is the displacement of the engine. As we all know, a higher displacement engine produces more power as it imparts larger amounts of torque to the crankshaft via the pistons with each combustion cycle. The engines of the 883 and 1200 Sportster are no different in size if you looked at it outside. It simply has larger bores; approximately 3.5 inches to the approximate 3 inch bore of the 883. Simply put, the 1200 Sportster engine has a bit more material and weighs slightly more than the 883 engine; the difference in weight is too small though to make a significant effect on performance.
If you have an 883 Sportster and you want to turn it into a 1200 Sportster, some shops are able to do it for a price. The process is quite intensive and requires the disassembly of the engine. It is then re-bored to increase the displacement and the pistons are then replaced to match the new bores. Other aspects and parts of the engine are then tuned to match the modifications of to the bore, and the end result is an engine that is very similar to a 1200 Sportster with a matching performance increase.
Although you can upgrade an 883 to match the 1200 Sportster, it involves a lot of work and the end result greatly depends on the work quality of the one who did the work. Needless to say, it also voids any warranty you have with your Sportster.
Summary:
The emblems are the only telling difference between the 883 Sportster and the 1200 Sportster
The 1200 Sportster has greater displacement than the 883 Sportster
The 1200 Sportster has a greater bore than the 883 Sportster
The 1200 Sportster engine is slightly lighter than the 883 Sportster engine
The 883 Sportster can be upgraded to equal a 1200 Sportster