Driver Knowledge Tests

How can you improve the acceleration of your car?

There are two ways to speed up your car’s acceleration:

  1. Improve its power output at the wheels
  2. Reduce any factors that are holding it back.

The driver

The driver has to choose the right gear for the speed, terrain and load (lower gears accelerate faster, but acceleration will tail off as revs reach their maximum).

The car could have different modes such as sport or comfort (sport mode will likely improve acceleration), or it might have a speed limiter.

Check that it’s not in ‘limp mode’ because something is wrong with the engine – there’ll be a red engine light on the dashboard.

The driver should be in the right seating position so that it’s possible to push the accelerator all the way to the floor, and there shouldn’t be anything stuck under the accelerator pedal. Finally, the handbrake should be fully disengaged.

Air conditioning takes power from the engine, so leave it off unless you really need it.

To get the best acceleration, learn about the characteristics of your car’s gearbox, and any features it has that might boost power. For example, a WRX STI has an intercooler spray that can be disabled or enabled (you’ll run out of water in the intercooler spray bottle frequently if you have it on all the time)

The mechanicals

Your car needs to have the right octane fuel to get the best out of the engine, but there are a multitude of other things that can be wrong with the engine that will cause sluggish acceleration, such as:

  • clogged fuel filter
  • malfunctioning mass air flow sensor or throttle position sensor
  • leaking or blocked hoses
  • clogged air filter
  • fouled spark plugs
  • blocked fuel injectors or fuel pump
  • timing belt out of alignment
  • faulty traction control sensors
  • worn clutch
  • clogged or blocked catalytic converter
  • carbon build-up in the intake manifold or other parts of the engine
  • leaking head gasket

A battery-powered car may not perform as well if the batteries are old or are depleted.

To get the best performance out of your engine:

  • ensure that all the above components are working properly
  • use good quality oil.
  • modify your engine (you can change the ignition timing, use a larger throttle body and injectors, increase the compression, and improve components that will reduce friction.)
  • make sure your tyres are pumped up to the correct pressure.
  • improve how your car breathes by fitting a turbocharger or supercharger (they force more air into the engine), or a velocity stack.
  • increase the size of your fuel line
  • install a dual-plane manifold
  • change the cylinder head

Obviously, some of those are expensive and may lead to a cascading need to improve other parts of your car, like the brakes and suspension.

Weight

If you’ve put bigger or heavier wheels on your car, they will take more energy to get moving. While wider tyres and wheels might give you more grip, they are also heavier.

If you’re carrying around unnecessary items in your boot, they’ll rob you of acceleration.

Balance weight in your car – lots of weight on one side makes it more likely your wheel will spin on the opposite side

If you’re carrying items on a roof rack, make them as aerodynamic as possible as wind pressure will fight against your car getting faster.

Therefore, to improve acceleration, get rid of weight. At the extreme end, you can swap out some metal components for lighter weight carbon fibre. Any easier option is to get rid of deadweight in your car.

Atmosphere

Three things conspire to rob you of power when you’re driving: temperature, altitude and wind.

A headwind will try to hold you back, and the air is less dense at higher altitudes and hotter temperatures which will reduce the efficiency of combustion in your engine.

Aerodynamics affects how the atmosphere will slow you down. The shape of your vehicle needs to be as slippery as possible – a roof rack, trailer, large spoiler and having your windows down will cause drag that will slow you down. You don’t need a spoiler unless you’re racing as they have limited effect under 80km/h, and they simply increase drag which increases fuel consumption, too.

To make your vehicle faster in hotter temperatures and at higher altitude, add forced induction (turbocharger or supercharger), or change the power source to batteries which aren’t affected by altitude.

Road

When the road is slippery the tyres will struggle for grip and will spin. Traction control can reduce the engine power and it will feel like you’re not accelerating as fast.

To improve this, use better tyres, make sure they are at the right temperature, don’t mash the throttle into the firewall, and try to avoid parts of the road with less grip (e.g. on a gravel road, a thicker line of gravel tends to accumulate in the middle, between the usual tyre tracks, and this will have less grip.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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