The Turbo Problem

  • September 7, 2023

You may have noticed that many new vehicles – most of them, actually – come standard with a turbocharged engine. It used to be generally true that only high-performance cars came with turbocharged engines.

There was a reason for that.

And it’s reasonable to be leery about why that reason has changed.

Turbos used to be used to make an engine a high-performance engine; often, the engine was already a performance engine. The classic example is the Porsche 911’s six cylinder “boxer” engine. It was already powerful – without the turbo. Adding the turbo made it even more powerful.

A turbo does this by using exhaust gas pressure (which spins a compressor) to pressurize the incoming air charge; instead of sucking it in – this is what naturally aspirated engines do – it is forced in. The additional air (and fuel) makes for a more powerful power stroke within the engine when the mixture is lit by the spark plug.

The end result is more power.

But also more pressure – on everything inside the engine. A more forceful explosion applies more force to the pistons and rings and then to the crankshaft and bearings – and so on. If the engine is small, it will typically have smaller surfaces to absorb all of this pressure, which concentrates the pressure.

The result – almost inevitably – is a shorter-lived engine.

Porsche 911 Turbos are fantastic cars but they are not generally cars that run reliably for 150,000-plus miles. That’s the price you pay for driving a 911 Turbo. It’s kind of like the price paid by body builders who take steroids.

They get pumped – but it doesn’t last.

So why do so many family cars – even economy cars – all of a sudden have turbocharged engines? The answer is straightforward: They don’t have enough engine. The turbo is there to make up for that. And you get to pay for it – in the form of a higher buy-in price and an increased likelihood of a shorter-lived engine

You can thank the government for it.

As an example – one of many – this week I am test driving a new Mercedes-Benz GLC 300, which is a crossover SUV that weighs 4,167 pounds. If it were 2013 rather than 2023, a vehicle this heavy would have come standard with a V6 engine around 3.5 liters in size. In fact, that is exactly what came standard in the 2013 Mercedes ML350, which was very similar to the current GLC. It was a little larger – and a little heavier – but the point is it came standard with a 3.5 liter V6 that didn’t need a turbo to move its more-than-two-tons of steel, glass and plastic.

The ’23 GLC 300 does – because all it’s got to move its two-tons-plus of steel, glass and plastic is a 2.0 liter four cylinder engine, which isn’t enough engine to move that kind of weight, without an assist.

Enter the turbo. It applies pressure when the driver imparts pressure – to the  accelerator. Without the pressure – from the turbo – there would be little in the way of acceleration coming from just 2.0 liters of engine, all by itself. The turbo makes up for what’s not there anymore.

Bu why is it not there?

Especially here – in a Mercedes?

2013 ML350

The ’23 GLC 300’s 2.0 liter four makes less power (255 hp) even with the assist than the old ML 350’s V6 (302 hp). It touts higher gas mileage: 23 city, 31 highway vs. 18 city, 23 highway for the old ML.

But do people who buy $50k Mercedes-Benzes care about that difference? Probably not many. But Mercedes has to care about it – because Mercedes has to deal with the government.

The otherwise insufficient 2.0 liter four that comes in the GLC300 is turbocharged to make the power people who spend $50k-plus on a Mercedes expect. But the underlying reason the 2.0 liter four is there is because a smaller engine scores higher on government fuel economy and lower on on government “emissions” tests. The latter in air-fingers-quote marks to mock the use of the term to describe non-reactive gasses that don’t pollute (carbon dioxide) as “emissions.” Which is kind of like using the word “vaccine” to describe a drug that doesn’t immunize.

Without the turbo, 2.0 liters would be a hard sell – in a $50k car.

Or even a $30k family car, such as a car like the Honda Accord – which also used to come with a V6 for that money. It now comes standard with – wait for it! – a 2.0 liter turbocharged four. So do many others. Some come with even less, as for example the 2024 Buick Envista I reviewed about a week ago. It only has 1.2 liters (and just three cylinders) to move about 3,200 lbs.

It wouldn’t move – without a turbo.

Without the boost.

But that comes with pressure – and that comes at a cost. It’s one almost everyone who buys a new vehicle will pay because adding a turbo and the peripherals (these include a specialized exhaust system and a higher-capacity cooling system to defray the additional heat produced by the turbo) costs money. And it is much more likely buyers will pay again, down the road – when the pressure results in a failure.

You could try sending the government the bill.

. . .

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