What Is Overboost?
Modern turbocharging technology has come a long, long way in the past two decades. Turbo lag, which is when an...
Modern turbocharging technology has come a long, long way in the past two decades. Turbo lag, which is when an engine builds boost higher in the rev range, is all but gone in modern turbo cars. There are also clever ways for car companies to give us a little more bang for our buck, pun intended, with turbo cars. One of these is a fun little thing called overboost.
For a comprehensive rundown on how turbochargers work, check out the guide over at our sister site The Drive! The differences between “twin-turbo,” “Bi-Turbo,” parallel, and sequential turbos has also been explained in a previous Car Bibles post; some other turbo terminology has been covered too.
But what is overboost? It sounds like something that’s outside the realm of the engine running reliably; it’s over-boosted, hopefully the engine doesn’t blow up! Again, luckily modern turbo technology has us covered here.
How does overboost work?
Overboost is a slight misnomer; what it really should be called is temporarily added boost. OEMs manufacture turbocharged engines to operate from the factory within certain parameters to operate as efficiently and reliably as possible. They keep boost levels safe to ensure this.
Overboost is when the the ECU temporarily operates slightly outside these parameters; it temporarily allows more boost pressure into the intake manifold. Usually, this causes the engine to temporarily gain around 10 percent more power for 10-20 seconds at a time, and only when beckoned. Meaning, when wide-open throttle (WOT) is happening, or the revs are above a certain level on the tachometer.
The best example is the Ford Fiesta ST: From the factory it normally operates at a maximum of 180 horsepower, but if the ECU detects some spirited intentions via the driver’s right foot, it’ll allow for more boost pressure that’ll net 197 horsepower.
There are actually two types of overboost.
There are two types of overboost! While I’m not sure exactly what the terms are technically called, I’ll just call them automatic and manual for convenience-sake:
- Automatic: the ECU automatically adjusts boost pressure
- Manual: the driver presses a button that toggles more boost pressure
The Fiesta ST is has automatic overboost, but the 2021 Hyundai Veloster N DCT has a button that toggles it. Hyundai calls it N Grin Shift; when the steering wheel button is pressed, torque jumps from 260 pound-feet to 278 pound feet for 20 seconds. While in overboost, more torque means more aggressive acceleration and faster revs. It ups the theatrics all around for sure! Once 20 seconds are up however, it can’t be toggled again for a few minutes. Presumably, this is to protect owners from potentially popping their engines.
It’s actually pretty cool that OEMs do this. They hear enthusiasts, and allow them a bit more fun to make the driving experience a tad more exciting, while still maintaining reliability. Though, some people say OEMs should just engineer their engines to withstand those higher boost pressures regularly. This is a good point, but also, what about an overboost function on that newer, higher number?
It’s a slippery slope; just be stoked that OEMs have our spirited driving in mind.