wy103: The Nosram and LRP are the same engine. The 12 size is manufactured by Picco and the 21 size by SH according to Nosram/LRP spec. I have been running the Nosram RS12 and RS21 - Special, both the engine run great and they are fast. However when running the the RS12, just make sure that you allow the engine to rev.
berky: Yes, the SH is indeed cheaper than the Nosram/LRP engine, but I believed they are some diff in quality and timming between them.