FX has made the following recommendations: 

• FXE659501: FX 2100 Tuned Pipe (Top Speed):
  
  
  
  
  • FXE659700: Short Manifold, Small Radius
    
  • FXE659701: Medium Manifold, Small Radius
    
  • FXE659702: Long Manifold, Small Radius
  
  
• FXE659502: FX 2108 Tuned Pipe (Bottom End):
  
  
  
  • FXE659704: Medium Manifold

Manifold Suggestions:

• Short: Suggested to be used for tracks with long main straights and to achieve the highest RPM but lower performance from bottom.
  
  
• Medium: Suggested to be used for medium or standard tracks.
  
• Long: Suggested to be used for short tracks where the performance from bottom is required but the RPM will be lower.