On flowmasters site it says that it is the one designed for smaller engines.
And I quote:
The 60 Series Performance muffler is designed specifically to bring Flowmaster performance to smaller cars and trucks with small displacement 4 and 6 cylinder engines. All 60 Series mufflers feature Delta Flow technology for increased torque, horsepower and reduced interior resonance.
Application Recommendations:
HighPerformance Street/Strip applications
Small Displacement 4 and 6 Cylinder vehicles
Sport Compact
http://flowmastermufflers.com/60_series.html