It used to be that engine displacement told you loads about the power output or a particular motor. Now, it’s a different story with turbocharged engines. Small displacement motors can now produce power and torque figures that rival and even beat naturally-aspirated engines with a larger displacement.
So, are turbochargers all good? Are naturally-aspirated motors obsolete? Which is better? Well the preliminary answer to all that is, it depends. There are several pros and cons to having one or the other. Let’s go over a few of them.
If you’ve done some research, you’ll know that turbocharged engines lag before they reach peak torque. If you’re starting at lower RPMs, exhaust gasses aren’t moving fast enough to spin the impeller that produces boost pressure. If you exercise a bit of patience or keep your engine speed up, the response is more immediate at the right RPMs.
There is no lag whatsoever on a naturally-aspirated motor. The only things standing between the air and combustion chamber are the air filter, throttle body, and intake valves. As your engine goes up in RPM, it sucks in more air, which is then supplemented by more fuel. Peak power is made higher up in the RPM range, and most new engines in the market come with variable valve timing that increases torque and efficiency at lower RPMs, and power and torque at higher RPMs.
Though, a counter-argument for turbo lag will be to go with a smaller turbo, a twin-turbo, or twin-scroll turbo. Variable turbos are also part of the equation and the main goal of these technologies and advancements is to eliminate lag and increase response. There is a case to be made.
Maintenance & Reliability
Whenever maintenance and reliability come up, a simpler system will more often be more reliable and more easily maintained. Fewer parts, mean fewer things to worry about, and naturally-aspirated cars are simpler than a turbocharged motor.
Turbocharged motors need oil lines routing to the turbine. It needs more vacuum hoses and space to fit in the turbocharger, the intercooler, and all the plumbing. Not to mention that a turbocharged car will definitely come with a different computer to accommodate all those sensors.
Now, no matter how many strides are made with regard to reliability, manufacturing, and engineering, natural aspiration is just simpler and easier to maintain than a turbocharged motor simply because it’s simple. Oh, and down the line, it’ll cost less to repair a turbocharged engine if and when it breaks.
Here’s where turbocharged motors can win over its naturally-aspirated rivals in a very simple way. There could be certain exceptions to the overview, however. Let’s compare a turbocharged 1.5L between an engine producing 2.4L worth of naturally-aspirated power.
See, with 1.5-liters of displacement, at idle, the engine will consume fuel enough to keep its smaller displacement running. Meanwhile, a 2.4-liter at idle will need more fuel to ignite 2.4-liters' worth of displacement to keep idling. When you get up and running, a naturally-aspirated motor will produce 2.4-liters worth of power, while a turbocharged motor will produce 2.4-liters worth of power, if not more. These are just estimates and simplifications, however.
The examples we’ve used here are the current and prior-generation Honda Accords, which have very different engines under the hood. As per our reviews, the old Accord was able to pull out 6.4 km/L in the city, and 16.1 km/L on the highway. In contrast, the new Accord netted 7.4 km/L in the city, and 17.4 on the highway. The marked improvement could be chalked up to the CVT transmission for the highway stride but is harder to deny while crawling in city traffic.
Power & torque
There is no doubt that turbochargers add power to an engine. Naturally-aspirated mills have less air to go by without a helping of boost. Torque figures are also substantially increased once a turbo finds its way into the engine bay. Adding a denser charge allows for a more explosive bang once the spark plug fires off, allowing for more force to push down on the piston, which in turn produces more torque.
On the flip side, certain strides are being made to alleviate the lack of torque from naturally-aspirated motors. Variable valve timing is one of the developments that helped engines have good low-end power, but high compression ratios have become a very effective way of extracting more torque out of a naturally-aspirated mill.
Mazda is a prime example of this. While other manufacturers are turning to turbo technology and electric motors to give their cars a boost, Mazda went back to the drawing board and took a page out of a diesel engine’s design book. The SkyActiv series of engines are proponents of this line of thinking. Making sure that the air-fuel mixture in the combustion chamber is as cramped together as possible allows for a more efficient bang once the spark plug goes off. New developments like the SkyActiv-X motor develops comparable figures to turbocharged engines.
In the vein of performance driving, the linearity of a naturally-aspirated motor allows the engine to lack an element of surprise. It is easy to predict an NA motor’s behavior because there are no spool-times, nor are there times when you drop out of boost. When you step on the gas, what power and torque you have is what you get.Turbo engines, when they spool up, produce a wave of torque that propels its speed all the way to redline. This surge of power may surprise and unwittingly break traction if a little too much gas is given.
In modern cars, however, traction control can smooth out throttle inputs, mitigating the turbocharger’s potency when the driver gets a little too excited.