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#15 by Turbinepowered on 17 May, 2007 12:36
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Quote from: "jtanguay"
maglev trains use electromagnets to float... the resistance isn't that much... i've also heard of plans to make a maglev train in a vacuum sealed tunnel... no friction means endless speed potential.
i can see a few problems with using an air cushion as a bearing replacement... hit a nice bump and the wheels will probably smack something.
The electromagnets aren't spinning inside each other's field in a maglev. And the fields are constantly changing to provide motive force.
Two constant fields, one spinning inside the other, will generate quite a bit of resistance. That's bare basics of how a generator works, and everyone knows those produce drag. Not as much as rubbing two bits of metal together, but not negligible like you want to think. -
#16 by stewardc on 17 May, 2007 13:12
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I think that if you'll read the original post, you'll see that I was simply interested in the differences and perceived advantages, if any. In my particular build, a VNT was never an option as, like everything else associated with the TDI, it's obscenely complex (just ask me...I've owned, and endlessly repaired, 2 of them). Once again, power and lower emissions, through electronics and other gadgets. That's why I'm building an AAZ. It's as simple as a 1.6, but with better power.
If you love VNTs, go buy and install one, but don't call me "absurd" for not wanting one. That's the beauty of this board. In most cases, the guys are willing to provide positive feedback when a question is asked. You, however, seem to think that yours is the only opinion with merit.
I suppose you'd never drive a Mk 1 either :roll: -
#17 by Turbinepowered on 17 May, 2007 13:46
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Quote from: "stewardc"
I think that if you'll read the original post, you'll see that I was simply interested in the differences and perceived advantages, if any. In my particular build, a VNT was never an option as, like everything else associated with the TDI, it's obscenely complex (just ask me...I've owned, and endlessly repaired, 2 of them). Once again, power and lower emissions, through electronics and other gadgets.
VNT doesn't require the electronic controls. It can be controlled quite nicely with a cable, some springs, and a boost-actuated diaphragm of some sort.
Just pointing that out. -
#18 by stewardc on 17 May, 2007 14:11
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Quote from: "Turbinepowered"Quote from: "stewardc"
I think that if you'll read the original post, you'll see that I was simply interested in the differences and perceived advantages, if any. In my particular build, a VNT was never an option as, like everything else associated with the TDI, it's obscenely complex (just ask me...I've owned, and endlessly repaired, 2 of them). Once again, power and lower emissions, through electronics and other gadgets.
VNT doesn't require the electronic controls. It can be controlled quite nicely with a cable, some springs, and a boost-actuated diaphragm of some sort.
Just pointing that out.
Thanks, but they are known to fail regularly (seize up), where the old style turbo is pretty well bulletproof. How do I know this, you ask....because I had 2 and replaced a number of turbos. This is something that was unheardof in the past. -
#19 by 935racer on 17 May, 2007 14:20
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Whoa easy guys, I don't think anyone is trying to piss anyone else off here, lets keep this board chill.
Personally I hate VNT turbos, they are neat piece of engineering sure, but made to cover up a lack of engineering else where that I happen to take a lot of pride in. I'll take ball bearing or journal bearing turbos over vnt any day, although some of the newer VGT turbos I might consider. -
#20 by jtanguay on 17 May, 2007 14:45
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well like i mentioned before, a regular maintenance item if you have the aforementioned mechanical VNT setup, all you need to do is mash the accel pedal a couple of times to *free* the vanes... also the fact that the vanes move with the accelerator cable position is even better.. constantly moving vanes can't seize up too good.
either way if you use VNT or not, i'm sure your beast will run good and strong!
i think the main reason andrew is pushing the vnt is because he's driven with it on a 1.6, and the driveability is pretty much night/day... just ask named tintin if he would switch back. :wink: as for reliability issues, that i do not know, but i intend to find out! :twisted: -
#21 by Turbinepowered on 17 May, 2007 15:13
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Quote from: "stewardc"
Thanks, but they are known to fail regularly (seize up), where the old style turbo is pretty well bulletproof. How do I know this, you ask....because I had 2 and replaced a number of turbos. This is something that was unheardof in the past.
Improperly cared for, even a journal bearing turbo can seize up in short order. 15 turbos in a single year on a 26-bus fleet. Those things are the size of my chest, and don't come cheap.
I have nothing against journal bearing turbos, ball bearing, foil bearing or VNTs either. Use whatever floats your boat. I just wish you wouldn't dismiss the technology out of hand. -
#22 by foxracer1 on 17 May, 2007 21:06
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I've been thinking... would if the whole exhaust side of a VNT was coated with a ceramic coating. Not exactly sure of the properties or characteristics but wouldn't it be kinda of "slick" and not allow carbon/soot to stick? Just a thought. Also it would be more efficent due to the decrease of heat(energy) loss.
I'm not sure of the thickness of all the coatings out there but obviously you wouldn't want to decrease the thickness any with all thse moving parts. -
#23 by DVST8R on 17 May, 2007 22:41
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Quote from: "libbybapa"
Actually a seized wastegate (open or closed) is far from unheard of. Actually fairly common.
I also do not agree that VNT turbochargers are used to simply cover up for poor engineering. Given a specific engine and standard turbo combo, then there is a VNT that will simultaneously spool faster, give more max boost, flow better at higher rpms, and have a higher efficiency. With a standard turbo, you must take your pick what you want. With a VNT you can have it all.
Again, I couldn't care less what turbo someone else installs, but I will respond to what I feel is misinformation.
Andrew
Well then I will have to respond to what I feel is misinformation.
The VNT has no way of changing the max boost, the vnt is only on the turbine side of the turbocharger, your max boost is determined by the compressor map of the.... you guessed it compressor side. Yes a VNT will spool faster as it has a varible A/R ratio, the problem with this is that you get into a performance application of this turbo and you run into compressor surge, this is already seen as soon as the GT2056V (better known as the VNT-20) which is the common upgrade for the TDI and our motor. If you take a look at the VW motorsports paper it shows this in there compressor map that they did for the race car with a bunch of the first plot points outside of the surge line. With the TDI you can tune the surge out by slowing down the rate of spool, which is the exact reason that you wanted the VNT in the first place. Infact one of the common faliures of the VNT is a broken shaft from surge, where people goto WOT at low rpm's and stall the compressor and break the shaft.
So now on to the effciancy, the compressor effciancy is the same be it wastegated or not, as seen by the compressor map, and seen by the fact they use the same compressor vnt or not.
As far as the efficiancy of the turbine, the VNT is actually far less effciant on this side becuase of the drag of the vanes amongst other things, this is seen in both turbine effciancy maps, as well as in the high drive pressures they create, which cause high egt's, high oil temps, ect... It is because of this that you don't see them being used in gas applications (other then the new porsche 911) as the create the big drive pressures and create more heat, in a gas app there is already more heat, putting it past the fatigue point of most known metals.
As far as flow at high rpm's on the compressor they would be equal on the turbine, it would depend. If you had an a/r equivelent to the vanes at there max postion the VNT would not flow even close to as much, do to drag on the vanes as well as the housing design to hold the vanes.
As far as effciancy I think we have covered that.
I'm not going to get into which one fails easier as I can blow either one up easy.
Now before everyone who is on the VNT band wagon kicks and screams. Here is where they are superior:
Giving a wide tourque band in a specific application, such as a daily driver, or a modest performance vehical. Which is 98% of the builds that I see going on here.
The VNT is NOT the be all end all, and yes it does have some engineering flaws when compared to the newest breed of the VGT's, but this was a starting point to build to that turbo. The VNT is old school in varible turbo's, as such there will always be something newer faster and better.
I will give you a hint as to why the new VGT's are so much better. Imagine varible compressor, and turbine.
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#24 by stewardc on 18 May, 2007 03:20
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Finally, information instead of ***ing. Great article. Good work.
I think I'll stick with the T3 for now, and watch VGT development for the future.
Thanks again. -
#25 by subsonic on 18 May, 2007 08:10
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Ok, I am going to take a risk and jump into the thread. Im not throwing behind either "side", although it would be nice if everyone took a chill pill :!: :wink: Just had a friendly question.
I had read that on some of the new 2008 design diesels that they had designed a system to purge the catalytic (sp?) converter when it soots up by temporarily raising the EGT's to a very high level to cook it clean.
Would the same principle be of use to help the VNT vanes from getting gunked up and hindering there movement? Someone here had mentioned that something like that could be a problem on the vnt.
I am sure there are good reasons to use various turbo setups, old style, ball bearing, vnt etc, based on many variables. All have pluses and minuses. It could be as simple as " This is what I had on my shelf, I'm broke so this is what I'm using." to wanting the newest high speed, nearly indestructable, teflon coated, lightning proof, gee wiz marval of modern engineering.
If people here are asking questions, it's because they are seeking knowledge. Thought processes are bases on what we think we know. Perhaps people should give everyone a bit of a grace period for the thought processes and knowledge gained to sync. No need to be grinding gears :wink: Over time everyone will ask a bad question. Over time everyone will fire off an answer that might be considered a bit harsh. It happens. Things change, people will chill.
Of course if they don't, whip out the flame thrower and burn baby burn.
Got all that from my Dr. Phil correspondence course.
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#26 by stewardc on 18 May, 2007 09:17
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I'm gonna wade right in here again, and state that no offence is intended nor implied by me. I'm sorry if anyone is bothered by my posts.
I don't believe I ever stated that a VNT wasn't technologically superior to older styles of turbocharger. I only stated that the technology is the problem, for me (maybe not for you).
I only wanted to know what perceived advantages there were to ball bearing turbos, and what was available. How this got to a VNT vs not-VNT fight is beyond me.
Focus, people :wink: -
#27 by jtanguay on 18 May, 2007 19:19
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#28 by burn_your_money on 18 May, 2007 19:47
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http://www.youtube.com/watch?v=321LwkM7i90
I beleive this is the cat purging system that was discussed