Many people dream of owning a Ferrari, cruising in it through Monaco and going in it to play Blackjack in a casino. They don’t realize that Ferrari ownership comes with $5,000 maintenance appointments, $400 tires and the frustration that they will get from sitting in traffic and looking for parking will be much higher compared to owning a regular car.
It works in a very similar way with advertisements of new flashy products that you see in magazines and online. A straight-through exhaust may look great on your car and even add 10-20 horsepower, but it will also turn a quiet luxury car into a loud endlessly buzzing vehicle. The expense of replacing a simple catalytic converter will also be much higher after you install the exhaust system while the 10-20 horsepower addition will only happen at the very top peak of the rpm range.
The reality behind car modifications that improve the performance of your car is such that these modifications always come with compromises. In the example with the exhaust system, your car will look better and gain more horsepower, but the driveability would suffer because of the additional noise and the torque in the midrange, which is where your engine is on most days when you drive in traffic, would go down.
In the same way, a spring and shock absorber modification would most likely hurt ride quality while at the same time improving control in corners.
A turbo kit that can give you a lot of extra power will need a new clutch, an upgraded fuel system, gauges and more. In addition to these extra expenses, you will lose the engine warranty, which means more expenses if something happens to the engine.
The list of such examples could go on and on. The conclusion here is simple: when investing in a performance upgrade for your car, do your homework and make sure you understand where your car will become better and what sacrifices you will have to make.