My fiesta feels like it gets power out of nowhere.

[throwaway]

Hello,

I'm pretty new with cars in general but I recently got a ford fiesta vignale and I was just wondering if anyone can explain what happens in this particular situation.

For example, I'm accelerating in 2nd gear and then around 20-23mph, my car feels like it unleashed a lot of power from nowhere and accelerates like a madman. When this happens, my car feels like it changed gear by itself (it pauses for a split second) and then accelerates with much more power. This also usually happens when I'm accelerating quite quickly. I'm just curious as to what's going on here.

Thanks in advance!

[Aldridge Andy]

Do you have automatic or manual transmission?

 

if auto it could be “kick down” and the auto box changing down to maximise performance for swift overtaking.

if manual, as revs increase you hit a point where the turbo is spinning nicely and you can make some swift progress. ( this is the sweet spot the auto gearbox will try to achieve when you kick down ) 

[throwaway]

1 hour ago, Aldridge Andy said:

Do you have automatic or manual transmission?

 

if auto it could be “kick down” and the auto box changing down to maximise performance for swift overtaking.

if manual, as revs increase you hit a point where the turbo is spinning nicely and you can make some swift progress. ( this is the sweet spot the auto gearbox will try to achieve when you kick down ) 

I have a manual, I had a small suspicion it was something to do with the turbo. So does that mean that the car decided that it needed to use the turbo to gain that extra power?

[unofix]

1 hour ago, throwaway said:

So does that mean that the car decided that it needed to use the turbo to gain that extra power?

It only thinks that when it's in a hurry to get to the pub !

[Chrissy_J]

Yeah, that's the turbo doing it's work. Nowt to worry about 😊

[fiestaecoboostman]

This has to be a wind up.

[Eric Bloodaxe]

I've seen a few "before and after" power/torque graphs on tuners websites which show maximum torque occurring around 2500 rpm which would be about 20-25 mph. (We don't know whether the OP has a 125 or 140 which has slightly lower overall gearing). 

So yes, if you put your foot down at that sort of speed in 2nd the car will accelerate quite briskly. I wouldn't say "like a madman" though, depends what you've experienced previously, I guess.

[TomsFocus]

I remember getting my first turbo car...  Boost did feel 'like a madman' compared to the wheezy NA's I'd been used to before that!!   

I did learn in a turbo diesel, but it was only a 1.4HDi which didn't appear to have a power band, it was so horrendously slow you couldn't even tell when the turbo was boosting!  

[Marky146]

Turbodiesels are generally quite linear. You don't have a throttle on a diesel so its spinning up quite early TBH. 

It's easy to think it as a wind up, but a lot of people have very little understanding of how engines and ancillaries work.

Here's a 101.

An internal combustion engine (ICE) is in essence an air pump. It sucks air in and then adds and burns fuel to increase volume to push the piston down and then exhausts it.

As revs increase the exhaust flow increases. A turbocharger places a rotating turbine wheel in the flow and this speeds up and the attached compressor wheel then forces air pressure upstream of the engine. this in turn increases power and exhaust pressure quickly until the Electronically controlling boost pressure is reached, when a valve sends pressure to an actuator to bypass exhaust gas around the turbine. This means you get the power the same on hot days as cold, atop the M62 or indeed up the Sustenpass in the Alps as at sea level.

Often the turbo speeding up quickly gives a lag sensation or a sudden surge. if you use a light foot pressure and raise the revs to 3,000 for example, then put your foot down, you'll get acceleration and shortly after a stronger surge. If you boot it from 1,500rpm, you'll feel the power build slowly then suddenly pick up. 

Finally smaller turbos spin up from lower RPM and give smaller boosts, larger ones spin up only from a higher RPM but produce more power on boost. 

The size of the engine under it can determine steady off boost economy and behavior. It's why the Ecoboost 1.0litre cars are so good. Bugger all pumping losses and small engine economy and a healthy boost from the turbo to make it flow about double what it would otherwise. 

The ST has a 1.6litre turbo and is a very flexible car. You can hold third into most tight corners and it just drives out. You learn to moderate the throttle more as it can go from deep booming torquey car to screaming banshee with very little effort. ***** good fun though. This from an ex WRX STi Impreza owner....