What dis??

My fella bought my wreck off me and then bought the crashed one from the auctions. Both 6's are 03 model except mine was a month older.
The thing is... one has K2 (the younger one I think??) on the engine and the exhaust... the other has K1 on the engine and exhaust.
WTF is K1 and K2? does that make a difference to any of them?
The thing is... one has K2 (the younger one I think??) on the engine and the exhaust... the other has K1 on the engine and exhaust.
WTF is K1 and K2? does that make a difference to any of them?