What is overboost and how does it work?


VW, Ford, Hyundai, etc., are pumping themselves up, literally, with the hi-tech miracle of so-called overboost - but what exactly is it?


The Hyundai i30 N - awesome hot hatch - manages 353 Newton-metres from 1450-4700.

Or, on overboost, 378 Newton-metres from 1750-4200.

That’s about seven per cent more.

Should you buy one of these overboosted vehicles? Do not waste time looking for a button or diving into the menu system - there’s nothing for you to activate. Overboost is just there, enabled, all the time.

It’s really just part of the engine management software implementation for a turbocharged engine.

What happens is: the engine control computer waits for the right set of conditions:

For example, in the i30 N you’d need to be inside the rev window - 1750-4200 - big throttle input, temperature in the green, it might only work in some gears (I don’t know).

There’s a bunch of inputs - pre-conditions that have to be met.

See also:

The ECU gets a whole bunch of ‘go’ inputs for overboost, it opens the vanes up in the turbo and allows a bit more exhaust flow, driving the turbo a bit harder. More boost, hence the marketing wank name.

And it starts a timer - that’s important.

The turbo delivers slightly more boost - you get more mass flow of inlet air into the engine. The ECU increases the fuel injector flow to compensate. More fuel gets burned per unit time.

You get more torque at the crank. Torque x revs = power. Therefore, more power at those revs.

When Hyundai talks about the torque boost at those revs they’re really talking about a seven per cent increase in power at those revs. Same thing - but it’s harder to quantify the power.

More heat gets produced, too. And heat kills things like turbos and pistons, inconveniently, expensively, so the timer limits the duration of what would otherwise be too risky an operation if it were open-ended in the time domain.

Overboost forever equals a loud noise and deafening silence, plus a repair bill you can’t jump over, basically.

You get maybe 10 or 15 seconds of this increased output, and then, literally, normal programming is resumed. It’s all automatic.

So, yeah, the increase is real, but modest, and very brief.

So: overboost is there. It’s mostly just hype - sounds good on the right kind of car - and if you really need it to get around that truck, you’ve already made a bunch of quite poor decisions about overtaking, in my view…

Deep-dive into the secret life of turbochargers >> at Wikipedia.


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