Getting a boost: Types of turbos

Getting a boost: Types of turbos

Types of turbos - car engine

Forced induction is often a quick way to eek out as much horsepower from a car as possible.

Coupled with an intercooler, a turbocharger (or turbochargers) is a very effective component utilised by manufacturers and enthusiasts alike to add performance.

What might surprise some is just how much choice is available on the market – so when you’re looking into boosting your pride and joy, there might just be a little more homework to do than you thought.

There are six main types of turbo, all offering their own set of benefits and drawbacks – let’s dig into what they are.

Single Turbocharger

The most commonly used type of turbocharger, a single turbo will be most people’s view of this component.

A single turbo is quite flexible in how it can be manufactured and, as a result, how it can affect your car’s performance.

Compressor wheel size and a turbo’s turbine can both lead to inherently different characteristics of a turbocharger. In addition, the overall size will also play a big part in what a single turbo can offer.

While a smaller single turbo will give you great low-down torque thanks to their fast spool speed, a large single turbo will offer you greater top-end power.

Single Turbo Advantages

  • Cost-effective way to increase engine power & efficiency
  • Simple construction allows for easy install
  • Great for allowing smaller engines to challenge larger naturally-aspirated power units

Single Turbo Disadvantages

  • Narrow rev range; will need to choose between low-end grunt vs high-end power
  • Turbo response can be sluggish in comparison to other turbo setups


As you might expect, this is where an additional turbo is added into the mix.

Twin-turbocharging brings with it extra flexibility, as well as additional power – the ability for sequential turbocharging, for example, sees one turbo deal with low-end torque, while the other brings the power in the top end.

Alternatively, for V-type engines, one turbo can be added to one bank of cylinders and the second turbo to the other.

Twin-Turbocharger Advantages

  • Sequential turbocharging allows for a flatter torque curve, giving useful torque in the low end, while power doesn’t tail off at high revs

Twin-Turbocharger Disadvantages

  • Doubling the turbos means double the cost, and twofold complexity
  • Not necessarily the answer to such needs twin-turbocharging can bring

Twin-Scroll Turbocharger

Now things start to get a little more complicated – twin-scroll turbochargers are an intelligent form of forced induction, where air is being fed through on a cylinder-by-cylinder basis.

An example of this would be where, on a four-cylinder engine, cylinders one and four could feed to one scroll of the turbo, while two and three feed to the other.

With this in play, the gases are moving around much more efficiently, resulting in purer, denser air hitting each cylinder.

Twin-Scroll Turbocharger Advantages

  • Much more effective than single-scroll turbos
  • Creates more impactful energy into the exhaust turbine to conjure more power
  • Wider rev range boost can be made available

Twin-Scroll Turbocharger Disadvantages

  • Far more complex than traditional turbo designs
  • Needs a specific engine layout and exhaust design to work

Variable Geometry Turbocharger (VGT)

Moving onto a very specialised type of turbo, VGTs are a touch costly but are incredibly effective at forced induction.

A VGT makes use of internal vanes which are in place to alter the area-to-radius (A/R) ratio to match the engine’s revs.

Down in the rev range, the A/R ratio is kept low to spool up the turbocharger quickly – then, as the RPM gets higher in the range, the A/R ratio widens to allow for increased airflow.

VGT Advantages

  • Similar to twin-turbocharging, a VGT can offer versatile boost to across the whole rev range
  • Only requires a single turbo, removing complexity

VGT Disadvantages

  • Not really for petrol-powered application, and only typically found in diesel-powered powertrains where the vanes can’t be damaged by heat
  • Costs to make them effective for a petrol-powered vehicle are high, as exotic metals are required to help reliability

Variable Twin-Scroll Turbocharger (VTS)

Combining the best of a twin-scroll turbo and a variable geometry turbo, a variable twin-scroll turbocharger (VTS) allows for use more easily in a petrol-powered car than a VGT, thanks to its cheaper and more robust design.

A VTS can work in two ways – either redirect the exhaust airflow to a single scroll, or vary the amount its valve opens to allow for the gases to split to both scrolls.

VTS Advantages

  • Notably cheaper to manufacture than the VGT equivalent
  • Can be applied easier to petrol engines
  • Wide, flat torque curve

VTS Disadvantages

  • Still particularly more expensive than a single turbo or traditional twin-scroll
  • Hasn’t necessarily caught on as a technology

Electric Turbocharger

If there’s one thing that people might have a moan about when it comes to turbos, it’s lag.

However, if your turbo has an electric motor in the mix, lag quickly becomes something of the past, as does the likes of not having enough exhaust gases or perhaps a lack of low-end torque.

In an electric turbocharger, the motor is there to spin up the turbo’s compressor from the off to immediately boost low-end torque – then, when power from the exhaust volume is high enough, this can take over as normal.

Electric Turbocharger Advantages

  • Practically eliminates turbo lag
  • Increases the RPM band that the turbo will effectively work within
  • Potential to recover wasted energy (see Formula 1)

Electric Turbocharger Disadvantages

  • Issues around cost and complexity are immediate, thanks to the addition of the electric motor
  • Adding a battery into the mix (to power the motor) requires additional thought when packaging the components
  • You’ll find slightly comparable benefits with a VGT or twin-scroll turbo for a lot less money