Turbo venting pressure at speed?

[Zebbie]

Hiya,

The turbo seems perfectly ok accelerating 1st/2/3 at revs, but for example i'm doing 100K's and go to overtake up a long hill (In 5th) , I hit about 110-120K's and the car *stutters*, with what sounds like the turbo dumping all pressure, and the boost reading bounces all over the place.

If i back off on the accelerator, it will immediatley settle down.

Thoughts?

1996 GTST

T04 Turbo (Set to 13psi, manual setting)

Mines ECU

Nismo Fuel Reg

[Sydneykid]

Sounds like compressor surge to me, there are plenty of posts on that subject, I suggest you look it up.

[wreckedhead]

boost could be spiking and fuel is cutting out under load.

[51jay]

I would suggest dropping down to 4th in that particular situation..even 3rd if your feeling toey

[09ONE_32]

Yeah, I am going with what SK said. Not just because he is a guru, but I have the same problem only heaps worse. R32 GTST high flo R34 turbo. When I am in 5th driving on freeway even a slight hill, and I do mean slight, doing 3k if i go above 10vac, is will stutter shake the whole car boost gauge jumps like a ****er (it compressor surges) Problem being as my self diagnosis goes, is that the compressor wheel fitted is to efficent for the size of the exhaust turbine.

So at certin RPM and throttle positions the engines volumetric efficency is not great enough to use all the air the turbo is producing so it backs up and begins to compressor surge.

This is what I believe is happening anyway, but I am probably wrong so feel free to correct me.