Hi all, after resolving an issue with a missfire on my car (I asumed coil pack) but turned out to be number 2 spark plug only being held in by the coil pack! I have noticed that when accelerating foot to the floor the boost display on the dash fires to the top as expected but then declines to about half way from about 5krpm. I know on most maps especially with small turbos this isn't uncommon but is this what I should be seeing in the grande? I dont have a proper boost gague so its hard to know exactly what the boost is doing but you can certainly feel the torque tailing off. For reference it's a 180 bhp model.

Attached video...
[ame="https://youtu.be/X-Es0vJGOME"]https://youtu.be/X-Es0vJGOME[/ame]

That's normal, nothing to worry.

Full boost @ 1.3bar is around 2500rpm.

After that the boost is decreasing to about 1bar and 0.8 near revlimiter.

I see that you are accelerating on high rpms so what you see it's normal.

Many thanks just what I wanted to hear, just wish it had a bit more poke... guess I'll have to upgrade!

There are mainly two ways used to control (limit) the turbo boost pressure:

1) Wastegate. Located either on the exhaust manifold or inside the turbo itself, when the boost pressure needs to be limited this valve opens to divert the exhaust gases from the turbo, hence reducing the turbo speed and therefore lowering boost pressure.

2) Variable geometry. Inside the turbo, there are vanes that direct the exhaust flow on the turbine, giving plus or minus efficiency depending on their position (angle).

Both are driven by an actuator (pneumatic or electric), itself driven by the ECU.

The variable geometry (most used on Diesel engines), allows quite big turbos to give some kind of boost at low revs, where a wastegated turbo wouldn't even spin, and also a proper boost at high revs/load. It cost much than the WG'ed and is more prone to carbon clogging, specially in urban vehicle...

Sorry for the theory but now You should understand why I suggest to check the boost limiter system: WG opening too soon, vanes locked at a certain point, leaks in vacuum hoses, etc.

Hope this helped a bit understand your car ? As usual, don't forget to update your post once you have some news to share !!

Regards, Bernie