The only difference between the 883 and the 1200 Sportster is the engine displacement. As we all know, a larger displacement engine produces more power as it imparts greater amounts of torque to the crankshaft through the pistons with each combustion cycle. The 883 and 1200 Sportster engines are no different in size if you look at it from the outside. It just has bigger holes; about 3.5 inches to the 883’s about 3-inch diameter. Simply put, the 1200 Sportster engine has a little more material and weighs a little more than the 883 engine; the weight difference is too small to make a significant effect on performance.
If you have an 883 Sportster and want to convert it to a 1200 Sportster, some stores can do it for a price. The process is quite intensive and requires the disassembly of the engine. It is then re-bored to increase displacement and the pistons are replaced to match the new bores. Other aspects and parts of the engine are then tweaked to match the drilling modifications, and the end result is an engine that is very similar to a Sportster 1200 with a corresponding performance increase.
Although you can upgrade an 883 to match the 1200 Sportster, it is a lot of work involved and the end result depends largely on the quality of the work of the person who did the work. Needless to say, it also voids any warranty you have on your Sportster.
The badging is the only difference between the 883 Sportster and the 1200 Sportster.
The 1200 Sportster has a larger displacement than the 883 Sportster.
The 1200 Sportster has a larger bore than the 883 Sportster.
The 1200 Sportster engine is slightly lighter than the 883 Sportster engine
The 883 Sportster can be upgraded to match a 1200 Sportster