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High Performance vs Fuel Economy

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What are the differences between turbocharging and supercharging? Is there an opportunity cost to driving an engine powered by one rather than the other? We weigh the pros and cons

Turbocharging and supercharging function as air compressors, to force feed additional compressed air into the combustion chamber. Resulting in larger volume of air to combust which equals to more power.

Turbocharging is powered by outgoing exhaust air to power the turbines, that compress the same exhaust air back into the combustion chamber. In essence, it recycles unused air that would otherwise be lost.

The turbocharger remains dormant below a certain RPM. To engage, an approximate range of over 3000RPM (Revolutions Per Minute), is needed to reach about 1.5 to 2bar (metric unit: 1bar = 14.5psi), of compressed air to provide the additional boost of power. The time taken to compress the air, causes a delay before the power is released. This is called turbo lag. Therefore, the additional turbo power is not delivered immediately and instantaneously. There are solutions to overcome turbo-lag.

Higher Power Output

Supercharging uses turbines, powered by the engine, that forces compressed air into the combustion chamber. The point to note is that power is taken away from the engine, therefore resulting in less fuel efficiency. The advantage is that power to the turbines is readily available. Therefore, the additional supercharge power is delivered immediately and instantaneously.

Power gains are significant. Conservatively, adding a turbocharger to a naturally aspirated engine will increase power by 30-50% and up. Adding a supercharger will increase power by 50-70% and up. Note that there are other factors to consider, which are not discussed, including many aftermarket products for turbo- and super- chargers.

For family cars, manufacturers can offer small- to mid-size car options with larger cabin and boot space, powered by smaller turbocharged petrol or diesel engine.  This offers more pulling power without sacrificing fuel economy.

For high performance, turbocharging offers engine-tuning opportunities across the torque range. There are OEM and aftermarket tuning workshops and products readily available. A thriving market, popular upgrades include products like intercoolers, bigger turbochargers, re-mapping software, and many others.  For modification guidelines, please refer to the Land Transport Authority (LTA) website.

Before making any modifications, you are advised to carefully review the vehicle owner’s manual or consult your dealer for the manufacturer’s recommendations. These recommendations are crucial as they ensure the optimal performance and safety of your vehicle. The modifications must comply with LTA’s guidelines, which ensures that road safety and standards for exhaust gas and noise emissions are not compromised.

Unauthorised modifications, including aftermarket turbocharging and tuning, can result in severe consequences.  Under the Singapore law, any person, including workshops, who illegally modifies or uses such vehicles can be fined up to $5,000, imprisoned up to 3 months, or both. The penalties for repeat offenders are doubled.
Hence, to avoid committing an offence, do not carry out unauthorised modifications to your vehicle.

Higher Costs

On the downside, the additional turbocharged power cannot be sustained for long periods. Moreover, when the turbocharger activates, fuel efficiency drops. The engine, and related parts, are constantly exposed to induced high pressure and heat.  Therefore, parts used in a turbocharged engine require better materials, bringing up cost. Maintenance cost, including parts and services, are higher as specialised knowledge is required.  Longevity of turbocharged engines relies on how the engine is managed.

Supercharging in family sedans is not common.  As the engine also powers the supercharger, they are paired with engines of higher capacities, often above 3- to 5-litres.  Mostly found in luxury sports cars and SUVs, poor fuel efficiency is expected.

The issue is further compounded by manufacturers choosing to go with the turbocharge route. Mostly because turbocharging offers comparatively better fuel efficiency. Therefore, with less supercharge powered engines, prices to buy one are higher which also increases maintenance costs.

Which is better? It is dependent on the manufacturers’ objectives for their various models. It is also a matter of market preferences, high performance vs. fuel economy, for family sedans or high performance cars.