Turbo surge protector..??

[Tintin]

I bought a vnt 25, the same one as Benjamin bought.

I notice that the compressor is very large and with A/R.61,  definitively this compressor is too large to support 30psi starting from 2000rpm on small 1.9L engine, there will be too much flow in proportion of the flow of this engine, the compressor take down (surge at low RPM)

I plan to put a small hose with electric solenoid valve (3/16 or 1/4 vacuum hose) to bleed some air from the compressor at low rpm, and starting from 2800rpm the valve will be closed.

The reason would be to make flow the turbo with its own flow at low rpm, and keep the desirable 30psi.

I do not see another solution, and I am likely to make a boathook?


Martin.

[RabbitJockey]

so basically you're makign a blow off valve that only opens at low rpms?

[Tintin]

humm!!  blow off vavle bleed too much air, that will kill the boost.

It is not for the overboost spikes,  but, when the turbos pump more air in the motor than the motor can physically flow through, then the air reverses back to the compressor, it's very bad for the turbo.

[Tintin]

a good link here: http://www.dresser-rand.com/controls/sc0498.htm

[935racer]

Tintin, is the compressor not already equipped with a surge overflow like this:
?

[Tintin]

935racer,  yes, it is a surge protector too, this turbo is probably conceived for its specific engine for work well at specific engine rpm range.

But, in my case, my turbo compressor is not like that, and it's a big turbo put in a small engine.

[935racer]

Can you post a picture of your compressor housing? It might be possible with some machining and welding to create a housing like the one I posted above.

[Benjamin]

this is it


i dont understand no anything from turbo surge, what can be damaged?
how do i know the turbo surge?

someone have a small easy explanation what this surge is

Greetz, Benjamin

[Tintin]

Yes, it's the same as Benjamin's turbo.

VNT25  and  VNT1749VA


To found the surge area of your compressor, it's complicated, but, found a compressor map on the net, and put your engine flow specification on it.

1.9TDI + VNT25 compressor like on the pic.....  :roll:  it's bad.....for low RPM,  when I have time, I make a photoshop and show you the engine flow on this VNT25 compressor map.

[Tintin]

someone have a small easy explanation what this surge problem is

Greetz, Benjamin

When the turbos pump more air in the motor than the motor can physically flow through, then the air reverses back to the compressor, it's very bad for the turbo.

[Benjamin]

like 935racer said, this will do the job, custom made.


But are those just a couple drills or how do they look inside?
how hard is it to know where to drill and how big... does it matter?

Greetz, Benjamin

edit, just found a close up in the "for sale" section. it looks like the "holes" are not trough.

[andy2]

There is no holes on the holset model.It has a ring type slot machined into the compressor inlet.This opened gap can be seen on an angle view form the inlet.The slot can be seen on the turbo pictured first on the previous post

[Benjamin]

found this

Surge is the left hand boundary of the compressor map. Operation to the left of this line represents a region of flow instability. This region is characterized by mild flutter to wildly fluctuating boost and “barking” from the compressor. Continued operation within this region can lead to premature turbo failure due to heavy thrust loading.
Surge is most commonly experienced when one of two situations exist. The first and most damaging is surge under load. It can be an indication that your compressor is too large. Surge is also commonly experienced when the throttle is quickly closed after boosting. This occurs because mass flow is drastically reduced as the throttle is closed, but the turbo is still spinning and generating boost. This immediately drives the operating point to the far left of the compressor map, right into surge.

Surge will decay once the turbo speed finally slows enough to reduce the boost and move the operating point back into the stable region. This situation is commonly addressed by using a Blow-Off Valves (BOV) or bypass valve. A BOV functions to vent intake pressure to atmosphere so that the mass flow ramps down smoothly, keeping the compressor out of surge. In the case of a recirculating bypass valve, the airflow is recirculated back to the compressor inlet.

A Ported Shroud compressor (see Fig. 2) is a feature that is incorporated into the compressor housing. It functions to move the surge line further to the left (see Fig. 3) by allowing some airflow to exit the wheel through the port to keep surge from occurring. This provides additional useable range and allows a larger compressor to be used for higher flow requirements without risking running the compressor into a dangerous surge condition. The presence of the ported shroud usually has a minor negative impact on compressor efficiency.

fig2

fig3


more can be find here
http://www.turbobygarrett.com/turbobygarrett/tech_center/Turbo%20Tech%20103.pdf

[shadowmaker]

I think that's an excellent idea tintin. We had bad surge with gt2252v in my friend's 1.9TDI. It occurred between 2000-3000rpm. Also turbine side made high EMPs after 4000rpm and we left it at 230hp, because there was no point to increase fueling anymore.

Now we are installing a gt2259v from 3.0TDI Audi on it and we hope to get more high end power this way. Surge might occur once again, but your genious idea can be the solution for it.

[Benjamin]

how much EMPs after 4000rpm? its my understanding the vanes are fully open when you measured this.

why do you think a gt2259v can flow more than a  gt2559v?

230hp is not that much, the other guy in a previous gt2559v post had 270-280hp on a 1.9td.

Greetz, Benjamin