The difference between BBR Tuning Racing Series Stages 1,2,3 and 4 is the high-performance parts added to the kit. They have the same base engine but each has different added high-performance parts included.
Stage 1:
Bonus- BBR Tuning Billet Aluminum High Compression Cylinder Head
Stage 2:
Bonus- BBR Tuning Billet Aluminium High Compression Cylinder Head
Bonus- BBR Tuning Speed Carburetor Air Filter (color subject to availability)
Stage 3:
Bonus- BBR Tuning Billet Aluminum High-Performance Cylinder Head 66/80cc
Bonus- 66/80cc High-Performance Carburetor
Bonus- NGK B5HS Spark Plug
Stage 4:
Bonus- BBR Tuning Billet Aluminum High-Performance Cylinder Head 66/80cc
Bonus - 66/80cc High-Performance Carburetor
Bonus – Expansion Chamber, Expansion Chamber with Muffler, or High-Performance Expansion Chamber
Bonus - NGK B5HS Spark Plug