Diesel cars with turbo lag: Is it really a deal breaker?

Turbo lag – a term one hears very often when discussing a diesel car. Buyers are confused when they hear a car has “turbo lag” – is it something to consider when buying a diesel car? Is it really such a big deal that it can make or break a purchase decision?

CarToq puts “turbo lag” in perspective for you and also lists the cars in order of the amount of turbo lag they possess, to help you make an informed decision.

Turbo lag is the jargon used to describe the slight lag in reaction time from when you press the accelerator pedal to the car actually surging ahead.

How to deal with turbo lag?

Dealing with turbo lag requires altering your driving style slightly. One needs to keep the car within its “power band”. What this means, is that you need to keep an eye on the tachometer and keep the engine rpm between 1800 rpm and 2500 rpm, where the most diesel cars develop peak torque. If you have to slowdown for a speed breaker for instance, downshift to second gear or even first if necessary to ensure the RPM is in this range, and you’ll be able to accelerate out quickly. Otherwise, you’ll lose a fraction of a second or so while the engine slowly builds up speed.

Some carmakers deal with turbo lag by reducing the gear ratio on the lower gears, which allows for the car to pick up faster in either first or second gear. Some more expensive cars employ a variable geometry turbo, which alters the rate of boost the turbocharger provides, thereby reducing the lag and allowing the car to get maximum torque across a wider rpm range. Smaller, inexpensive cars usually have a fixed geometry turbo, which have a very limited operating range and boost pressure.

If you are looking to buy a new diesel car, don’t let turbo lag influence your decision drastically. Turbo lag can be dealt with by a slight alteration in driving style – the Renault Duster 110PS for instance has notorious turbo lag, yet it is a fun-to-drive vehicle. The Volkswagen Polo too has quite a bit of lag, but is a very popular car.

Diesel cars with the least turbo lag

Many popular diesel cars are notorious for this “turbo lag” but yet continue to sell very well. That means driver’s are doing something right to deal with this turbo lag. CarToq experts Shreyans Jain, Devdath Narayan, Mandar Ketkar and others picked out a list of diesel premium hatchbacks in India and ranked them order of increasing turbo lag – from the one with the least turbo lag to the one with the most. The cars with the least turbo lags are the ones that are immensely drivable in the city, as they don’t need to be revved much.

Premium diesel hatchbacks in India in ascending order of turbo lag:

  1. Nissan Micra / Renault Pulse diesel
  2. Toyota Etios Liva GD
  3. Ford Figo TDCi
  4. Chevrolet Beat diesel
  5. Fiat Punto diesel 75 bhp
  6. Maruti Swift diesel / Maruti Ritz diesel
  7. Tata Indica Vista diesel
  8. Fiat Punto diesel 90 bhp
  9.  Hyundai i20 diesel
  10.  Skoda Fabia diesel / Volkswagen Polo diesel

From this list you will notice that the Nissan Micra and Toyota Liva are cars that have almost no turbo lag, but yet these are not the most popular premium hatchbacks. In fact, the some of the best-selling cars like the Maruti Swift are in the middle of the pack, while the second-best selling premium hatchback – the i20 diesel is at the bottom of the pack.

This goes to show that even though these cars may have turbo lag, it’s not a factor that hampers a purchase decision as drivers learn to deal with it.

What is turbo lag? Detailed explanation!

garrett-turbocharger-photo

Turbo lag is the jargon used to describe the slight lag in reaction time from when you press the accelerator pedal to the car actually surging ahead. This lag usually comes in diesel cars that have large turbochargers to develop more torque, but this peak torque only comes in when the engine revolutions per minute (RPM) is around 2000 rpm or so.

To understand why this lag occurs, one must look at the function of turbochargers. What a turbocharger does is to compress air to a higher atmospheric pressure and force it into the cylinders, as this leads to much better combustion and better power output from the engine.

Turbochargers are turbines which have a turbine that spins off the exhaust gases on one end and on the other end an impeller sucks in air from the air filter and forces it into the engine intake manifold at high pressure. Because a turbocharger works off the exhaust gases, it needs a certain velocity of exhaust gases coming out of the engine to build up speed.

The lag happens when the car is at too low rpm and there are not enough exhaust gases that are spinning the turbocharger fast enough. Once you press the accelerator pedal, it takes a second or so for the exhaust gas velocity to increase, thereby increasing the spinning rpm of the turbocharger, consequently increasing boost pressure in the engine and giving you the acceleration you desire.

how-turbocharger-works-photo
How a turbocharger works. Image courtesy: Mazdarotary.net

Share your thoughts on turbo lag in diesel cars – is this a key deciding parameter for you when buying a car?