Why is turbo lag a thing?

A turbo is a impeller that is spun via exhaust gas. It then spins an impeller that sucks in air, pressurises it and forces it into your engine. So your turbo takes something that you weren’t using anyway and turns it into more horsepower. Add in the fact that it often makes your car more efficient and you have to love them.

Turbo lag is the biggest drawback to a turbocharged engine. Car makers are trying to get rid of it, but that’s easier said than done.

If you want to learn a bit more about engines and even how to drive better, this is the article for you.

How do turbos work?

To understand turbo lag, we have to have a fundamental understanding of turbos. So here’s a real simple, real easy explanation.

When the exhaust valve opens, the piston forces the exhaust out of the valve and through the exhaust tubes. The turbo is fed by all of the exhaust tubes, this exhaust pressure is what spins the impeller. This impeller is connected to the intake impeller.

What the intake impeller does is rotate and suck air into it, compress it and send it to the intake manifold. Imagine trying to put a sponge in a box. If you just drop it in, you get one sponge in the box and that’s it. If you force sponges in, compress them and wedge them all in there, you can get maybe 5 sponges in the box.

The more air you force in, the more fuel you can force in. If you increase the amount of air/fuel in the combustion chamber, you increase the potential energy of the combustion. Bigger explosion = bigger power.

So by the exhaust gas increasing as rpm increases, you’re forcing more and more air into the engine as rpm increases. The more air you force in, the more exhaust you force out. It’s almost self perpetuating. This is how a turbocharged engine delivers so much more power than a naturally aspirated engine.

That sounds fantastic, so what’s the big deal?

First off, it is fantastic, turbos are cool.

Secondly, let’s elaborate on the last part of the “how they work” section.

So your turbo is spun by exhaust gas. Therefore it needs a certain amount of exhaust gas to operate. The impellers are designed to be as effective as possible, where the engineer wanted them to be.

So if your engine makes peak torque at 3500rpm and peak horsepower at 6250rpm, that means you engine is running at full chap between 3500rpm to 6250rpm. So what’s happening below 3500rpm?

That’s the thing, as you get close to peak torque, the turbo is spinning faster and starting to effectively compress air.

But if you’re low in the rpm range and floor it, the exhaust gas isn’t strong enough to spin the turbo up fast enough. This creates a lag between when you want the power and when the turbo can deliver the power.

Voila! That is turbo lag. It’s the time you have to wait for the turbo to spool up and get ‘on boost’