From the
370z weight reduction thread you can see it gains 11.3 pounds but that can be offset will high flow cats
STILLEN Exhaust
Muffler Section - 39.6lbs (proven huge hp gains)
Y-Pipe - 11.3lbs
Resonated Y-Pipe - 14.4lbs
Total: 65.3lbs
Difference: +11.3lbs and 18whp
The Berk Cats are 5.5 lbs a piece for 11 lbs total, versus 21 lbs for stock.