Car and motorcycle tuning.

I used to be a Yay-sayer. I've spent thousands of dollars on extra parts for numerous bikes and cars. Looking back, barely a single add-on has ever worked as well as I'd been told it would. 
Manufacturers really know what they are doing. They work very hard to make their products as good as possible, within the price range, with standard equipment. If you want more performance, go up in price range, don't buy add-ons.