35 psi boost and resultant running problems

[regcheeseman]

Finally, I've got my VNT controller running properly and took the car for a decent 100 mile test run, it's just had the gearbox replaced as well.

I've also got a boost gauge fitted for the first time, it's a 30 LED bargraph and calibrated to 30 psi.

Driving out on the A roads, taking it steady and the boost seems to be fairly tame, around 12psi peak and I'm beginning to wonder if the turbo is capable of actually delivering much boost. However 6 miles into the journey the single lane switches to dual lane and there’s a queue of traffic up ahead. I give it some pedal and the boost is up into the 20's, but I back off as someone pulls out ahead of me, they realise the mistake and pull back in and I'm back on the loud pedal - boost is now off the gauge and charging hard - Suddenly BANG!, huge cloud of black smoke and the gauge drops to 0.

I pull over and refit the boost hose. (something I would be doing a fair bit during the day)

It was on the journey home I notice the problem, the boost is building very quickly, and during a spirited charge in second gear the gauge is straight past the red limit and the motor stumbles/misfires, chucks out a cloud of white smoke and then after a second or two, clears and runs fine.

Any idea what is happening?

[carrizog60]

mine did that once,revving the engine in neutral.my vanes are opening at 1 bar so the same thing happen but at only 1 bar.
missed a bit,white smoke but then it returned to normal.


so i will be looking this thread with attention lol

[Alcaid]

Isn't this the recipe for destroying your turbo?!?

[regcheeseman]

What's a recipe for destroying my turbo?

If I knew what was happening then I'd do something about it.

Maybe fit a wastegate?

[Alcaid]

Is the VNT controller reacting too slow to the changes?

[rallydiesel]

What turbo do you have again? Boost spikes of 35 are very bad for the small vnts. 25 psi spikes should be the absolute max for a vnt15 or similar.

[keaton]

What vnt controllers you have?

[rodpaslow]

With my late experience if it's a vnt 15 I don't think it can sustain 35 psi without having issues like what you've described only mine was catastrophic failure of the turbo.  My opinion after cleaning all the oil and replacing my head gasket is that the turbo is pushing oil into your intake, maybe for only a second or two, your engine is burning it (white smoke) and is then fine for a while.  My turbo pushed about 1 1/2 litres into the intake and engine as it was failing.  My $.02

I'd like to try that vnt 22 I've seen with modified bearings and seals - 25 to 35 psi would be easy for it.

[RabbitJockey]

yes my engine smoked alot of white when it was running away, this makes a bit of sense.  it also could simply be getting into the exhaust.

[regcheeseman]

What turbo do you have again? Boost spikes of 35 are very bad for the small vnts. 25 psi spikes should be the absolute max for a vnt15 or similar.

No I have a proper turbo not a toy one   It's a BV39A-0072 IIRC and it's pushing 30 psi easily

Is the VNT controller reacting too slow to the changes?

possibly or the map isn't right at the moment - it gains revs and boost at an incredible rate - mash the pedal in second and it'll bury the guage almost instantly.

Now that I've learnt to go a bit steady on the pedal - but I was curious what was happening?

[Alcaid]

BV39 from a PD100 or PD105 pushing 30psi... Has overspeeding and ultra low efficiency written all over it... 

[rallydiesel]

Just cuz it pushes 30 psi easily doesn't mean it should. BV39 is what is on the BRM. It's actually a pretty stout turbo. But tuners generally map for 18 psi sustained with it. Any more and you should go to a larger turbo.

[RabbitJockey]

are you monitoring emps?

[regcheeseman]

emps? 

Just cuz it pushes 30 psi easily doesn't mean it should. BV39 is what is on the BRM. It's actually a pretty stout turbo. But tuners generally map for 18 psi sustained with it.

How do I stop it making 30 psi then?

Has overspeeding and ultra low efficiency written all over it...

No signs of ultra low efficiency - my god it shifts 

[keaton]

try this controller

http://dmn.kuulalaakeri.org/vnt-lda/


does VNT & LDA control (boost enrichment)