Is it time to send the old naturally aspirated engine to an early grave as modern engines adopt the turbocharger?
I love a good naturally aspirated (NA) engine, especially on a high-performance model. The high-revving nature of the motor and the unfiltered sound from the exhausts are addictive, but non-turbo engines may have had their day...
A naturally aspirated engine has fewer moving parts than a turbocharged motor, therefore many will expect its proven technology to hold the edge in terms of reliability. What's more, a century's worth of engine efficiency development and driver education has rendered the free-breathing engine economical to operate as long as a measured driving style is the order of the day. However, despite improvements in engine technology, such as the introduction of variable valve timing, to name but one example, naturally aspirated (petrol) engines cannot match their turbocharged (petrol) counterparts in terms of delivering maximum torque at low rpm. And it's an impression borne from driving turbo- and non-turbo vehicles randomly, as we motoring journalists do.
My average daily drive features a mix of start/stop traffic. There's a hustle-and-bustle dual carriageway that requires ducking between stopped buses and taxis and a short stint on the freeway. I imagine this is not too dissimilar to most people’s average commute. I’ve driven hundreds of different cars down this stretch of road during the past 6 years and I can tell you I dread having to drive a car with a naturally aspirated engine, especially in short succession to a turbocharged (petrol) motor. Now, I’m not talking about high-performance naturally aspirated engines (such as those in Lamborghinis), those still have their place in sportscars and supercars (more on this later), what I’m talking about is the run-of-the-mill 1.2, 1.6, 2.0-litre and all the variants in between.
Even BMW M engines have moved into the realm of the turbo
Most people know that in order to keep fuel consumption down you need to change gears at low revs, use smooth throttle inputs and generally keep the engine rotating as few times per minute as possible. It’s very easy to do, shift early, maintain speed and become a pro at predicting traffic lights. Of course, you still have to compromise between how slow you’re willing to go and how late you intend to be. I try to maintain a decent compromise but, unsurprisingly, err towards the faster side of things, while trying to stay to the speed limit as best as possible.
This is where the naturally aspirated engine is found wanting. Keep a low rpm and try and accelerate quickly and… nothing happens. Work the gearbox down a couple gears, get the engine spinning at mid to high rpm and you get some kick. It’s a hard graft having to do that over and over on a commute. It’s not much better on the freeway either, if you lose a bit of momentum behind another car, you’re back to working the box and revs to get back up to speed. It’s not just about having to work the gearbox – you can get an automatic to do that for you if you want, it’s the aforementioned vital torque statistic that lets it down as well. By contrast, a car with a smaller-capacity turbocharged engine can produce the same (or more) torque lower down in the rev range.
Here’s a quick comparison between a pair of small crossovers that we had in our fleet at the same time: the Suzuki Vitara's 1.6-litre naturally aspirated engine produces 86 kW and 151 Nm – a decent power output, but maximum torque is at 4 000 rpm. A 1.2-litre 3-cylinder turbocharged Citroen C4 Cactus produces 81 kW and 205 Nm of torque, where maximum torque kicks in at 1 500 rpm. That means, as long as you’re travelling in the teens in terms of engine speed (revs), when you put your foot down, you get maximum torque – without needing to shift gears or spin up the motor.
Citroen Cactus uses a 1.2-litre turbo motor
Then there’s the fuel economy factor. The official claimed fuel consumption figures of small-capacity turbocharged engines seem very optimistic and are usually better than those for similarly-powerful, bigger-capacity petrol motors, but I’m not a big believer in the former numbers. I’ve found that turbo-engined compact cars do tend to use more fuel than what their manufacturers claim, but in the case of the Citroen, the higher consumption (relative to the crossover's performance characteristics/general drivability) was quite acceptable. Let me explain: We reset test cars' trip computers when they arrive at our office and monitor the fuel efficiency readouts of their onboard computers (granted, this is another can of beans waiting to be opened) so that we can record readings upon completion of the tests. The Suzuki, after 3 800 km, averaged 6.7 L/100 km and the C4 Cactus, after 5 100 km, averaged 6.5 L/100 km.
It’s a reasonable comparison: both cars were driven by the entire test team on long and short journeys. The funky Citroen is 55 kg lighter than the more practically-packaged Suzuki and its indicated consumption figure is 1.8 L/100 km higher than what its manufacturer claims; the Suzuki proved anything but thirsty (we achieved a figure just 0.9 L/100 km higher than what the Japanese firm says it should be). However, given that the indicated consumption figures of the cars were within a whisker of one another, and the C4 Cactus offers more responsive and flexible performance, I prefer its engine to the Vitara’s.
Suzuki Vitara features a 1.4-litre turbopetrol motor in the UK. I have driven one and its engine performance is much perkier.
It’s not like turbocharging is new. As far as petrol engines in South Africa are concerned, the technology went on hiatus for a couple of decades. However, whereas the turbopetrol motor was synonymous with performance in the '80s, these days it's the flagbearer for downsized efficiency, especially in compact cars. It started locally with the Ford Ecoboost 1.0-litre engine, then came the Renault 0.9-litre 3-pot and since then it has crept through to just about every manufacturer. Even the premium brands have adopted turbocharged triples: BMW has a 3-cylinder powering a 3 Series and Audi has a 1.0-litre A3.
What is apparent, however, is that the Japanese and Korean manufacturers have been less eager to introduce small turbocharged engines in their line-ups, especially on the local market. There are a number of factors to consider: those firms pride themselves on reliability/low warranty claims and turbocharged engines, which are more complex and mechanically stressed than their tried-and-trusted naturally aspirated counterparts, present a higher risk of failure (and would be expensive to fix if/when they break). The extra complexity adds to the production costs of turbopetrol motors and, therefore, the units in which they're installed. And, needless to say, the profit margins are tight in the as-much-spec-as-possible compact hatchback and small crossover segments.
But the market never stands still. Hyundai and Kia have selectively rolled out the 1.6-litre turbocharged GDI motor, Honda recently introduced a 1.5-litre turbopetrol in the Civic sedan, Toyota (having introduced a forced-induction 2.0-litre in its Lexus line-up) has a 1.2-litre turbopetrol in the pipeline that might debut in the C-HR small crossover. Meanwhile, Mazda is sticking to its guns with its SkyActiv engine efficiency technology and as for Suzuki, the upcoming Baleno compact hatch may be offered with a 1.0-litre turbopetrol motor – at some point, but that remains to be seen.
Audi's R8 V10 is possibly the last bastion of the naturally aspirated engine
Yes, not every single petrol engine needs to be turbocharged, but I would argue that most of them do. Just as technological advancements in smartphones (and the data networks through which they operate) have raised users' expectations of their handsets to such an extent that their consumption patterns are based on market activity rather than their actual needs, "the turbo era" is breeding a generation of motorists who want instant torque and good efficiency.
The disadvantage of a naturally aspirated engine is that although conservative buyers will duly expect excellent reliability from it, a test drive in a "free-breathing" car directly after one in a direct "turbo'd" rival will leave them feeling somewhat short-changed. Drivability/driving satisfaction may not be equally important to all consumers, I realise, but once naturally aspirated engines are in the minority, they will seem increasingly undesirable to car buyers who are all too happy to leave worries about reliability to the companies that underwrote the (often lengthy) warranties that come included with brand new cars.
I do believe naturally aspirated engines have their places. One is in bare-bones budget cars and the other is where they can deliver the maximum enjoyment and the fewest drawbacks – high-performance machines. A naturally aspirated motor that can be revved until it bounces off a limiter north of 7 000 rpm is a treat and, for a petrolhead, few sounds can match the V10s or V12s built by supercar producing firms whose wares can bring tears to grown men’s eyes. These "free-breathers" should either bring mobility to the masses or joy to enthusiasts. But in an everyday car or family car? No thanks, I’ll stick with the turbo.
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