Does the Zetec S have overboost on the 125ps engine?

Yes

is overboost a physical "thing" or a software thing?

Software. It's time limited to 15 seconds I think.

This may (or may not) help the OP. In my old 1.4 "Hi-Torq" orsa I only used 1st to get moving, 2nd was then fine for acceleration. This is a no no in the 1.0 ecoboost turbo. If you try that, when you hit 2nd you'd prolly push the car faster ;) If you're in a queue of traffic you can edge forward/pull away at tickover (~1000rpm), if you want to pull away faster (no traffic) you need to hit 1500rpm (when the turbo kicks in) before engaging the clutch. You need to stay in 1st until at least 2500rpm, then, when you hit 2nd, the revs will fall to ~1500 so still in turbo range. I find a decent gear change is at ~3000rpm (i've never been over 4000rpm since I got the car), I don't see the need. Around town following Lemmings, 3rd is the way to go. You can just about manage 30mph in 4th although the engine is close to labouring. The biggest prob I find is when you approach a roundabout at ~15mph looking to "slot in" to a gap. If you're in 2nd and make an insertion, the go pedal does the square root of bu**er-all, but, the book says not to go into 1st above 15mph. I still haven't mastered this :)
HTH.

I always thought you had to let a turbo car tickover before you stop the engine as the turbo loses its forced lubrication,not cooling, when the cars oilpump stops,thus starving the turbo's bearings of oil.The turbo's of old had "floating" main bearings and could reach100,000 rpm.The little Ecoboost turbo can reach 250,000 rpm flat out so unless Ford have designed some way to keep the oil pressure up for a while after stopping the engine i would let the car tickover for a short time.

As above really, unless you have been running on full boost it should be ok to turn off after a few seconds. Letting it tick over allows the turbo to slow down enough that when you switch off the time without oil flowing is reduced.

As its a small turbo it should slow fairly quickly, I've seen a big turbid focu RS get switched off and you could still hear the turbo whistle like it was ate high enough speed for boost.

Lack of lubrication is more critical than lack of cooling, although both are required for the turbocharger to operate effectively and as far as I know the oil ceases to circulate once the engine is off, although as previously stated, the water cooling continues for a short period after the engine is shut down, however as the vehicle is no longer moving there is no forced cool air entering the engine bay & cooling system therefore the electrically operated water pump will not be as efficient at cooling as when the car is moving

Leaving the engine to idle for a short time is good practice.

Has anyone done a remap on the fiesta titanium 125 and if so did you have to change the pressure valve on the turbo, any help would be great please??

 

Whenever I've done a fast run up the M1 I've noticed that when I switch off something in the engine compartment keeps running for a while.

As long as the car is at tickover it's safe to turn off. Sometimes coolant will continue to circulate if needed.

According to the ford owners manual for vehicles with a turbocharger you should not switch the engine off when it is running at high revs (not sure why you would want to do that anyway)

Release the accelerator pedal and wait for engine to return to idle speed. See pic attached .

I've always switched the engine off a few seconds after it's returned to idle.

3 hours ago, Blatto said:

According to the ford owners manual for vehicles with a turbocharger you should not switch the engine off when it is running at high revs (not sure why you would want to do that anyway)

Release the accelerator pedal and wait for engine to return to idle speed. See pic attached .

 

The fact they feel they have to write that in the manual says something about new Ford buyers! 

Who's sitting in thier driveway with the throttle wide open before switching off!?

 

Back in the day you'd get people advocating blipping the throttle just before switching off.  Idea being it would coat the top end of the engine, cams and rockers with oil.  To protect on next startup.  This was when oil pumps were crap.  I remember the days of a couple of seconds of rattle on a cold start.

I've got 64 plate 1.0 eco boost fiesta zetec s I just wanted to know does it even have a turbo on it 

12 hours ago, mikee745 said:

I've got 64 plate 1.0 eco boost fiesta zetec s I just wanted to know does it even have a turbo on it 

Yes.

13 hours ago, mikee745 said:

I've got 64 plate 1.0 eco boost fiesta zetec s I just wanted to know does it even have a turbo on it 

It's under the shiny heatshield at the front of the engine, see below:

7 hours ago, Eric Bloodaxe said:

It's under the shiny heatshield at the front of the engine,

I always thought that was a 'blast proof' cover for when the engine goes "Boom" 🤣