504355 / 504355 - Application Notes Weights: Stock Exhaust Muffler Section - 26.8lbs (highly inefficient) Y-Pipe - 11.6lbs Resonated Y-Pipe - 15.6lbs Total: 54.0lbs 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 Also note that the weight is at the lowest point of the car, over the rear wheels, which will increase traction.