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Engine Specific Info and Questions => TDI Engine -General Info => Topic started by: Tintin on May 06, 2007, 08:29:32 am
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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.
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so basically you're makign a blow off valve that only opens at low rpms?
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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.
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a good link here: http://www.dresser-rand.com/controls/sc0498.htm
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Tintin, is the compressor not already equipped with a surge overflow like this:(http://i94.photobucket.com/albums/l83/935racer/CIMG6827.jpg)
?
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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.
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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.
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this is it
(http://img275.imageshack.us/img275/1903/pict0057ui2.jpg)
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
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Yes, it's the same as Benjamin's turbo.
VNT25 and VNT1749VA
(http://img181.imageshack.us/img181/4220/im001789ib4.th.jpg) (http://img181.imageshack.us/my.php?image=im001789ib4.jpg)
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.
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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.
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like 935racer said, this will do the job, custom made.
(http://img459.imageshack.us/img459/9642/customsurgeslot758ip0.jpg) (http://imageshack.us)
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.
(http://i55.photobucket.com/albums/g136/zacstevens/DSCN0157.jpg)
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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
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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
(http://img405.imageshack.us/img405/1033/fig2enlarges113rf8.gif) (http://imageshack.us)
fig3
(http://img405.imageshack.us/img405/1033/fig2enlarges113rf8.gif) (http://imageshack.us)
more can be find here
http://www.turbobygarrett.com/turbobygarrett/tech_center/Turbo%20Tech%20103.pdf
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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.
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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
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With 1,6bar boost EMPs were reaching 3bar. So we didn't want to start adding fuel, although there's plenty room for that.
I didn't say that gt2259v is better than gt2559v, did I? It just that it's from a car that makes 230hp originally and has much better flowing turbine than gt2559v (newer desing).
I do have experience on both of them. On my 2.5L van I used gt2559v some years ago. I wasn't happy with it as it didn't tolerate boost over 1,5bar (1,7bar boost made 5,5bar EMP). I currently have wing from gt2259v (from Audi 3.0TDI) planted inside gt20. I'm running it with 2,2bar constant with almost equal EMP on my Volvo 2.4D.
Well, at least we are going to try this. Maybe it will work, maybe not.
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Now, surge is just basically an audio resonance, correct? A low frequency sound (pressure) wave bouncing back and forth. Couldn't it also be delt with from that angle also, by trying to remove the elements that support resonance, like smooth transitions? Any audio engineers out there? Just wondering.... Also do cars without IC's (very short tube runs) suffer from surge?
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i dont understand no anything from turbo surge, what can be damaged?
how do i know the turbo surge?
The rapid airflow changes puts huge amounts of stress on the compressor wheel. If the surge is strong enough or it occurs for too long it will prematurely wear out the thrust bearing or, in the worst case, snap the shaft.
If the turbo surges, you will hear a sound like loud scissors or barking.
Here is a video with a perfect example of what turbo surge sounds like: http://www.youtube.com/watch?v=mHmdO350xcY
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Here is a garrett GT30R with an added surge protector housing.
(http://i121.photobucket.com/albums/o237/mesojdm/P1010010.jpg)
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With our MB project we have to deal with surge when gas pedal is lifted up. We are concerned that our GT37vnt won't take the abuse much longer so we decided to put a dump valve in it. Usually it's not necessary to use dump valve on diesels, but clearly that's not the case here. With 85mm compressor we are able to reach over 1,0bar boost @2000rpm. :wink:
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So what valve did you use, and how did you set it up?
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I got an idea. I have an external wastegate that I wasn't going to use. I will reduce the spring pressure so it opens at a low pressure, 2-5 psi. I will then fit a solenoid valve in the air line to it, and put a switch that only closes at low pedal settings. That way I won't loose boost except when it exceeds the spring setting and I let off the throttle. Plus I already have the valve. :twisted:
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With our MB project we have to deal with surge when gas pedal is lifted up. We are concerned that our GT37vnt won't take the abuse much longer so we decided to put a dump valve in it. Usually it's not necessary to use dump valve on diesels, but clearly that's not the case here. With 85mm compressor we are able to reach over 1,0bar boost @2000rpm. :wink:
i dont understand very well, you mean after full throttle you leave the pedal and you have surge? i thought a diesel had the same engine-air-flow when it was in free-load and under-laod becouse you dont have a thotlle?
i also thought it had an anti surge stock, a picture from a previous picture from your MB project
http://i19.tinypic.com/2djv59d.jpg
i wonder where you can get bigger plungers for the inline pump from the MB300td. Like to know more :D
Greetz, Benjamin
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I made my dump valve and screwed around with it for a bit. It would dump down to 6 psi with the only weaker spring I could find that would fit. It would still surge a bit although some of that could have been due to the actuation point of the switch. So I worked on the spring a bit so it would have less force, and tried again. This time the spring was weak enough that it would open the wastegate at 15 psi just from pressure on the valve alone, with nothing going to the diaphragm. I also changed the switch, so it would open the valve to the diaphragm sooner. No surge this time! Then I decided I better hook up the actuator for the vane control as it was getting no boost. With the engine getting revved a bit and the vanes closed, the actuator came down and opened them, like it was supposed to. I decided to disconnect the solenoid to disable my dump valve and see what happened. Well, with the actuator working, I no longer got surge as it wouldn't let the turbo build up as much pressure. Guess I should have hooked it up before I wasted my time making the dump valve. The only good thing is all my plumbing is still in its design phase and made out of ABS for easy and cheap modification. Anyway,
for reference, here are the pics before I take it all off.
(http://www.66rover.com/temp/dump.jpg)
The wastegate dump valve.
(http://www.66rover.com/temp/switch.jpg)
A small reed switch, which is controlled by the small rare earth magnet on the pump lever.
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You can only used the selenoid valve to bleed extra air flow (boost), it is more than sufficient, I did not test yet, but according to some experience with all turbo, when there is a little leak or ¼ disconect pipe on the IC piping, the boost fall very low, that takes a very small hole to remove much pressure and/or some air flow.
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i dont understand very well, you mean after full throttle you leave the pedal and you have surge? i thought a diesel had the same engine-air-flow when it was in free-load and under-laod becouse you dont have a thotlle?
i also thought it had an anti surge stock, a picture from a previous picture from your MB project
http://i19.tinypic.com/2djv59d.jpg
i wonder where you can get bigger plungers for the inline pump from the MB300td. Like to know more :D
Greetz, Benjamin
Yep, I thought the same, but you can hear the surge noise very clearly, when you back down the pedal. Don't know why, although we are puting huge amounts of air into this engine at low revs.
That's a gt42vnt in the picture. We are using gt37vnt in the car. Gt42vnt might be too big...
We have something like hundred modified MB inline pumps here in Finland. There's a shop called Mynä Diesel and they can do this for you. Some of those cars have dynoed over 500hp with silly sized Holsets. We just are the first ones to use vnt with these beast.
jimfoo: We are just planning things out at the moment. Although I don't see anything difficult with it.
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maybe its a stupid question, but its my understanding a turbo can only have surge problems on boost, i know when you hear much turbowissle (also offboost?) its something to take a look at, but the most important is when you have it on boost the gauge reads no paeks and hills.
offcorse once you leave the pedal, and the vanes close before the boost is gone, you have more backpressure, in this case maybe a dumpvalve should be something good? but you can also change your settings from the vane-vontrol. anyone else have heard about this problem ever?
Greetz, Benjamin
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You have surge when the turbo has built up a lot of pressure, then slowed to the point where the pressure it built up is more than it can make at the speed it is currently rotating. So the air tries to go backwards through the turbo, slowing it down, making the problem even worse until an equilibrium is reached. So yes, dumping the pressure when you release the pedal would help. If they made a reed valve, like 2 stroke motorcycles have, that flows enough, I bet that would eliminate it also.
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Here is an example of what surge sounds like. This is an extreme example because I completely blocked off the turbo outlet to force it into surge.
http://members.cox.net/lnewcomb99/Sound/LMNGT2256V-Surge_extreme_example.mp3
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when i pull to full boost, and i release on a high rpm, my turbo makes dumpvalve sound, is that surge also? Do i need to use a dieseldumpvalve?
now the vnt is even not fulle adjusted, the vanes dont close much when offboost.
Greetz, Benjamin
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Pretty much every stock diesel on the market will do that (Especially the Dodge/GM/Ford pickups in the states), it's considered normal and not really harmful.
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when i pull to full boost, and i release on a high rpm, my turbo makes dumpvalve sound, is that surge also? Do i need to use a dieseldumpvalve?
now the vnt is even not fulle adjusted, the vanes dont close much when offboost.
Greetz, Benjamin
No, that's normal when you are using high boost. Surge is a chattering sound and you can hear it very clearly at first and then it fades away. It's like TSAT-tsat-TSAT-tsat-TSAT-tsat
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Pretty much every stock diesel on the market will do that (Especially the Dodge/GM/Ford pickups in the states), it's considered normal and not really harmful.
If it isn't harmful then why would manufacturers bother spending the time and money to design surge protection into turbos? It puts a lot of stress on the turbo.
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when i pull to full boost, and i release on a high rpm, my turbo makes dumpvalve sound, is that surge also? Do i need to use a dieseldumpvalve?
now the vnt is even not fulle adjusted, the vanes dont close much when offboost.
Greetz, Benjamin
No, that's normal when you are using high boost. Surge is a chattering sound and you can hear it very clearly at first and then it fades away. It's like TSAT-tsat-TSAT-tsat-TSAT-tsat
to me that is the mostest coolest sound,lol
i make mine do it on purpose,sorta
wind it out in a gear,lots of boost....then push in the clutch,and shift grandma slow,,you get the chuffin sound
it sounds like rapid flatuation,,lol
:lol: :lol:
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Pretty much every stock diesel on the market will do that (Especially the Dodge/GM/Ford pickups in the states), it's considered normal and not really harmful.
:shock: :shock:
surge, not good in any way, shape, or form.
It's like spinning a bike wheel up and then shoving a stick in the spokes.
and hillfolk, that'd explain why your turbos blow so fast :wink:
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Pretty much every stock diesel on the market will do that (Especially the Dodge/GM/Ford pickups in the states), it's considered normal and not really harmful.
:shock: :shock:
surge, not good in any way, shape, or form.
It's like spinning a bike wheel up and then shoving a stick in the spokes.
and hillfolk, that'd explain why your turbos blow so fast :wink:
it was an answer to my quistion, we'r not talking about surge
Greetz, Benjamin
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oh ok, didn't read back any, my fault.
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Pretty much every stock diesel on the market will do that (Especially the Dodge/GM/Ford pickups in the states), it's considered normal and not really harmful.
:shock: :shock:
surge, not good in any way, shape, or form.
It's like spinning a bike wheel up and then shoving a stick in the spokes.
and hillfolk, that'd explain why your turbos blow so fast :wink:
one of the garretts blew a the exhaust wheel right out of the dp at the drags at the 1000 foot mark
(http://img19.imageshack.us/img19/7751/hpim01959he.jpg)
(http://img102.imageshack.us/img102/1574/hpim01941xs.jpg)
one of the kkk's let that lame thrust bearing go at hi revs+pumped about 1 qt of oil in the intake
so no that doesnt explain why im blowing turbos
maybe its because i let them go full boost(40+psi) ,and im seeing 1500degree exhaust temps
the turbine wheels are literaly melting off ,or getting fatigued