How do we value performance? Is it simply about power? When it comes to performance motoring, power is undeniably important. 0-100km/h timings, bhp figures, it's all part and parcel of the gamesmanship that comes with owning a performance car.

But power isn't an infinite, abstract quality. It exists in the real world, and that means coming to terms with the fundamental laws of physics.

So, how much power can a compact performance car have? How much should it have? 10 years ago, a Mk6 Golf GTI had 207bhp. Five years ago, the number seemed to be somewhere north of 300bhp. With the ever expanding arms race, we've now reached the point where a compact, 2.0-litre car is pushing upside of 400bhp.

Say what?

This here is the new CLA45 S, the newest fire-breathing member of the AMG family.

The car isn't shy about its performance capabilities. With its aggressive front fascia, stout stance, flared arches and quad-exhaust rear, the CLA45 is certainly eye-catching. Good-looking? I'm not sure. The grille is a little too shouty for my personal tastes. But, it's fitting that this car's loud looks match its loud character.

The interior is familiarly AMG - a modern, high-tech Mercedes cabin dotted with sporty (read: red) detailing.

Performance, then...

Let's get the big numbers out of the way first. The 2.0-litre engine pumps out a slightly ridiculous 416bhp and 500Nm of torque. 0-100km/h takes just four seconds (FOUR!). Top speed is 270km/h.

For some perspective, this car has more power (and just a tad less torque) than a C43 with a 3.0-litre engine, and has the same 0-100km/h timing as a (albeit heavier) C63 S with its 4.0-litre engine. Both of those cars are facelifted 2019 models. So, what the actual hell.

The outright performance capability of this CLA45 is shocking. Full bore acceleration kicks you violently in the back of the head on each upshift, and the car absolutely embarasses just about anything else on four wheels. 

The car rides firmly but reasonably, and handling is sharp and assured, thanks in part to the all-wheel drive system. However, if you have your foot fully down, I'm 100% sure that you're not thinking about anything else other than how damn fast you are going.

The CLA45 is massive out of corners, too. The 4MATIC+ system smartly shuffles power around, so when you put your foot down early, the car just shoots out of a corner in a way that is sometimes mind-bending. It's not exactly delicate, but damn is it effective.

Is there such a thing as too much power, though? 

This engine is extremely boost reliant, and it has to be. The laws of physics still hold, after all. To extract this much power of a (relatively small) 2.0-litre, Mercedes has done a ton of complicated fiddling with the engine.

It does mean that the car's feral character only comes alive above 3,000rpm. Below that, it's slightly lacklustre, as you wait for boost to build. This also means that if you leave it in the wrong gear while driving manually, power can take quite a while to come - sometimes, you can be on 50% throttle and still be waiting for the power to come. 

Sounds a little mad... 

To fully appreciate and use the car's monstrous performance, you have to drive it in Sport or Sport+ mode, and let the car do the complicated job of hunting the right gear such that you're always on boost. Do that, and the CLA45 is a right hoot.

What the car lacks in delicacy or driving nuance, it makes up for in sheer power and raw pace. And hey AMGs have never been known as delicate machines, eh? As a feat of engineering, the CLA45 is impressive. That Mercedes has managed to wring this much power out of a 2.0-litre engine is nothing short of black magic. Right now, it can claim the 'most powerful series production compact car' crown.

I'm personally unconvinced by this formula. Perhaps I don't judge performance simply via power figures, but I don't think a compact car should have this power. But then again, I'm exactly the sort of buyer that AMG doesn't care for.

In this arms race, numbers matter. And for drivers who care about these things, this car is sure to tingle their senses. Having the most powerful 2.0-litre engine ever produced is undeniable bragging rights.

And all those people who pull up next to you at the red light muttering on about how power isn't everything? Hit the gas, and they'll be far too small in your rear view mirror for you to hear them.

Need to see just what 416bhp means in this CLA 45S? We have just the thing...

How do we value performance? Is it simply about power? When it comes to performance motoring, power is undeniably important. 0-100km/h timings, bhp figures, it's all part and parcel of the gamesmanship that comes with owning a performance car.

But power isn't an infinite, abstract quality. It exists in the real world, and that means coming to terms with the fundamental laws of physics.

So, how much power can a compact performance car have? How much should it have? 10 years ago, a Mk6 Golf GTI had 207bhp. Five years ago, the number seemed to be somewhere north of 300bhp. With the ever expanding arms race, we've now reached the point where a compact, 2.0-litre car is pushing upside of 400bhp.

Say what?

This here is the new CLA45 S, the newest fire-breathing member of the AMG family.

The car isn't shy about its performance capabilities. With its aggressive front fascia, stout stance, flared arches and quad-exhaust rear, the CLA45 is certainly eye-catching. Good-looking? I'm not sure. The grille is a little too shouty for my personal tastes. But, it's fitting that this car's loud looks match its loud character.

The interior is familiarly AMG - a modern, high-tech Mercedes cabin dotted with sporty (read: red) detailing.

Performance, then...

Let's get the big numbers out of the way first. The 2.0-litre engine pumps out a slightly ridiculous 416bhp and 500Nm of torque. 0-100km/h takes just four seconds (FOUR!). Top speed is 270km/h.

For some perspective, this car has more power (and just a tad less torque) than a C43 with a 3.0-litre engine, and has the same 0-100km/h timing as a (albeit heavier) C63 S with its 4.0-litre engine. Both of those cars are facelifted 2019 models. So, what the actual hell.

The outright performance capability of this CLA45 is shocking. Full bore acceleration kicks you violently in the back of the head on each upshift, and the car absolutely embarasses just about anything else on four wheels. 

The car rides firmly but reasonably, and handling is sharp and assured, thanks in part to the all-wheel drive system. However, if you have your foot fully down, I'm 100% sure that you're not thinking about anything else other than how damn fast you are going.

The CLA45 is massive out of corners, too. The 4MATIC+ system smartly shuffles power around, so when you put your foot down early, the car just shoots out of a corner in a way that is sometimes mind-bending. It's not exactly delicate, but damn is it effective.

Is there such a thing as too much power, though? 

This engine is extremely boost reliant, and it has to be. The laws of physics still hold, after all. To extract this much power of a (relatively small) 2.0-litre, Mercedes has done a ton of complicated fiddling with the engine.

It does mean that the car's feral character only comes alive above 3,000rpm. Below that, it's slightly lacklustre, as you wait for boost to build. This also means that if you leave it in the wrong gear while driving manually, power can take quite a while to come - sometimes, you can be on 50% throttle and still be waiting for the power to come. 

Sounds a little mad... 

To fully appreciate and use the car's monstrous performance, you have to drive it in Sport or Sport+ mode, and let the car do the complicated job of hunting the right gear such that you're always on boost. Do that, and the CLA45 is a right hoot.

What the car lacks in delicacy or driving nuance, it makes up for in sheer power and raw pace. And hey AMGs have never been known as delicate machines, eh? As a feat of engineering, the CLA45 is impressive. That Mercedes has managed to wring this much power out of a 2.0-litre engine is nothing short of black magic. Right now, it can claim the 'most powerful series production compact car' crown.

I'm personally unconvinced by this formula. Perhaps I don't judge performance simply via power figures, but I don't think a compact car should have this power. But then again, I'm exactly the sort of buyer that AMG doesn't care for.

In this arms race, numbers matter. And for drivers who care about these things, this car is sure to tingle their senses. Having the most powerful 2.0-litre engine ever produced is undeniable bragging rights.

And all those people who pull up next to you at the red light muttering on about how power isn't everything? Hit the gas, and they'll be far too small in your rear view mirror for you to hear them.

Need to see just what 416bhp means in this CLA 45S? We have just the thing...