[Phantom]

Headers can help at lower speed driving but it depends on how bad your stock headers are. On my car the stock header is welded on the inside adding a turbulent restriction as the exhaust leaves the cylinder, from there the inside of the primary is between 10-18% smaller than the one on the rear this makes for slightly uneven power. Opening this up to match the back frees power and balances the performance. Some people that have replaced this report a small increase in MPG but they are driving for performance not economy.

Remember that this will not hold on all cars and each situation needs to be evaluated separately.