what is boost on a car

[SanKayden]

Boost refers to the positive pressure created by a forced induction system, like a turbocharger or supercharger, which forces more air into the engine's cylinders than it could draw in naturally. This is measured in pressure units like pounds per square inch (PSI) or bar. More air allows the engine to burn more fuel, which directly results in a significant increase in horsepower and torque without needing a larger engine displacement. It's the key to getting powerful performance from smaller, more efficient engines.

The primary goal of boost is to improve volumetric efficiency—how completely an engine can fill its cylinders with air. A naturally aspirated engine is limited by atmospheric pressure (around 14.7 PSI at sea level). A turbocharger, for example, uses exhaust gases to spin a turbine, which drives a compressor that packs air into the intake. If this compressor adds 10 PSI of boost, the engine effectively sees about 24.7 PSI of absolute pressure, a nearly 70% increase in air density.

It's not just about peak numbers; it's about how and when the power arrives. Turbochargers can suffer from turbo lag—a brief delay before boost builds when you press the accelerator. Superchargers, which are mechanically driven by the engine via a belt, provide immediate boost but are less efficient. Managing boost is critical, which is why systems have intercoolers to cool the compressed air (making it denser) and wastegates to control maximum pressure and prevent engine damage.

Here’s a comparison of how boost levels typically correlate with engine output in modern performance cars:

Boost Pressure (PSI)	Engine Type (Example)	Typical Horsepower Gain (Approx.)	Key Characteristic
5 - 8 PSI	Mild Turbo (e.g., many 4-cylinder sedans)	+20-40% over NA	Improved low-end torque, great for daily driving.
12 - 16 PSI	Performance Turbo (e.g., Volkswagen GTI, Subaru WRX)	+50-80% over NA	Strong mid-range power, noticeable turbo kick.
18 - 23 PSI	High-Performance Turbo (e.g., Mercedes-AMG 45, Porsche 911 Turbo)	+90-150% over NA	Extremely high power density, sophisticated cooling needed.
8 - 12 PSI	Roots-type Supercharger (e.g., Dodge Hellcat)	+50-100% over NA	Immediate throttle response, massive low-end torque.

Ultimately, boost is a brilliant engineering solution to the challenge of power versus efficiency. While it adds complexity, the trade-off is undeniable: you get the exhilarating performance of a much larger engine with the fuel economy of a smaller one when driving gently.

[GeorgeLynn]

Think of your engine like a big air pump. The more air you can shove in, the bigger the bang you get from the fuel. Boost is just forced air. A turbo or supercharger rams extra air into the cylinders. It's like giving the engine a shot of espresso. That's why a tiny 2.0-liter engine with boost can easily out-power a big old V8. You feel it as a shove in your back when the turbo kicks in.

[EmeryAnn]

When I first test-drove my car, the salesman talked about 'boost.' I didn't get it until I merged onto the highway. You press the gas, there's a second of calm, and then—whoosh—the car just takes off. It’s that surge of power that pulls you forward. For me, boost isn't a technical term; it's the feeling of having power in reserve. It makes passing slower traffic or getting up to speed effortless and, honestly, a lot of fun. It turns a boring commute into something exciting.

[CarlosFitz]

At its core, boost is about overcoming a fundamental limit. A normal engine breathes at atmospheric pressure. Forced induction creates pressure above that, increasing the air's density. More dense air means you can add more fuel, which translates directly to more power during combustion. The system's efficiency depends heavily on cooling that compressed air. An intercooler is vital because cooler air is denser and less likely to cause uncontrolled detonation, or 'knock,' which can destroy an engine. It's a precise balance of pressure, temperature, and fuel delivery.