View Full Version : variable area turbine nozzle

01-27-2005, 01:42 AM
any information on this?
maximum boost sort of confused me.
what controlls the boost? i realize the position of the vanes does, but what controls the position the vanes are in?
if anyone knows or has an article somewhere let me know please.


01-27-2005, 02:08 AM
I'm not 100% on this either, but the way I understand it, the vanes are controlled just like a wastegate would be, with a diaphram type acutator. I believe you still need to have a wastegate, as the vanes can't control boost well enough all by itself. Basically, when the compressor rpm is low and accelerating, you want the area to be small so the velocity is high. When the turbo rpm rises it doesn't need to accelerate anymore, and the vanes can open to maximize flow. This all occurs in a continuous fashion, the vanes don't just pop open all at once.

It's like getting the best of both worlds, a big turbo that responds more like a small turbo.

01-27-2005, 02:12 AM
im obsessed with them, i'll explain it as simply as possible, but theirs two different types

Type 1

this is garrets link and description (honeywell owns garret, but u can get this on ANY garret turbo thats why i call it garret ok?)

ok Garret makes what they call VNT (Variable Nozzle Technology) turbos, where very basically, to increase the boost at low RPMS the exhaust gas is forced through a smaller space, in order to make it travel faster.....this increased velocity (although more concentrated) allows the turbo to spool up faster

think of it as the end of a hose......turn on the tap.....the water comes out at a certain velocity, with a certain force. now squeeze the end of the hose, so the hole is only half the size it was......see how the velocity/power has increased? the water travels further doesnt it

same concept, at low revs, the gas is forced onto the turbine through a smaller area, thus increasing its velocity and power, and spooling up the turbo quicker......

Garret doesnt disclose much, so without looking at it, what i can decipher from their bullshit is that they have a nozzle, before the turbine, shaped much like the end of a jet engine on a fighter plane, that, once again, changes the outlet area (think mcdonnell-douglas f-14 Tomcats, F18's etc etc)

Type 2

now what Maximum boost explains is different again, and is what BMW have started using on their diesel powered 3 series in Europe (we dont get them in Aus coz our diesel has too much sulphur in it, i suspect the same applies in the US)

anway, imagine, if u will, the turbine housing of the turbo. imagine along the top of that, a series of Vanes, that look like those little straight pieces that run in a series in air conditioning vents.....if closed, the air would flow over the top, if opened the air would go through. these "vanes" are each on a shaft that adjusts their angle. when the angle changes so does the amount of flow, so at low boost, the vanes are less open, as to increase exhaust gas velocity, just as a nozzle.

if that doesnt make sense i can prolly draw some pics for u, but basically what ur looking at is low RPM boost in a turbo still big enough to make big numbers

01-27-2005, 04:19 AM
It's basically a variable A/R turbo, it can spool quick but also put out a lot of top end power, all due to varying the A/R.

01-27-2005, 05:48 AM
yes, thank you.
but does anyone have a very detailed description of exactly how it works and exactly what controls the vanes.

01-27-2005, 10:16 AM
You guys don't want ANY of that, trust me. It sounds like a wonderful idea, and it is, but it's NOT for street use. I've seen this firsthand. When I was 16 I used to frequent a shop called Import Specialties in walnut creek, california. They had an early 200SX, not sure what the year was, but it was a S12 chassis with a CA18ET motor in it. They built it up for serious high performance use, it was the first time I was introduced to two things, first being the Aerodyne Aerocharger, one of the first publicly available variable vane turbos, and second, a custom forged, non-twisted crankshaft made just for that car, destroking it to 1.4L. Everything worked GREAT for about 2000miles (it was built for the street) after that, it was a nightmare!

The problem is gasoline and street driving. Now, on a track most people run very clean (in terms of particulate emmision) gas, and don't do stop and go driving, so there are no real deposits to speak of, but on the street, it's different. We get silt and dirt and all sorts of shit mixed into our gas, and we also leave the engine idle for long periods, and that causes carbon buildup. Carbon buildup is the absolute BANE of a vane type turbo, it causes the vanes to stick and you get boost spikes, overboosting, and if it gets too bad, the actuator arm will actually twist off the vanes and send them into the turbine, fragging the whole turbo. This is exactly what happened with the 200SX, first it lost an engine to detonation from boost spikes, which happens ALL THE TIME, because the whole deal with the vanes is that if you foot is touching the gas and the engine is under a load, you're under max boost pressure. The constant spikes were enough to melt 3 of 4 pistons, and these were forged heavy duty pistons, not lightweight, but VERY dense. They finally narrowed it down to the turbo, and aerodyne replaced it under warranty. The second turbo lasted longer, about 3800 miles before one of the vanes snapped and grenaded the turbine! Aerodyne replaced that one too... the THIRD one suffered the same damned problem as the first, sticking vanes, and destroyed another $7,000+ motor, at this point aerodyne claimed the shop should have known the operating limits of the turbo and refused to honor the warranty.

I've heard similar results to EVERY person I've ever talked to who has run a variable nozzle, or vane turbo on the street. Such things just aren't possible with the gas we have today :( if you want a better spoolup, the best option currently is for a twin scroll housing, so unless you want a track only car, or you're willing to pull apart the turbo and clean it every 2000 miles, I wouldn't touch one with a stick. Sorry all :(

01-27-2005, 02:31 PM
Very interesting. I hadn't thought about that, but it makes perfect sense.

01-27-2005, 04:04 PM
thanks for trying to turn me away, but its not for a street car.
edit: i should say thanks for the heads up, i will keep that in mind :)

now if someone could offer some detailed information on how it works, especially some specifics what controls the amount of boost/position of the vanes it'd be very helpful.

01-27-2005, 05:51 PM

01-30-2005, 05:41 AM
thanks for the info MrWOT

i plan to run a VNT turbo on a car running EFI LPG (50% propane 50% Butane = 110 RON). its alot fuking cleaner than petrol, if u open up an engine thats been running pure gas for 500,000km u'll know what i mean, and changing the oil always seems like a waste, id be prepared to pull the turbo out every 4000KM's to chek just in case though, after reading that

oh and twinscroll was what got me into VNT ;)

01-31-2005, 02:46 PM
atm lag is good in a way...it keeps u slower ont eh street in most cases so u not go as fast adn thus keep lience...and also gives the guy in the other i thorught that he might beat u but then boost come and u spin the wheels past the V8 boy and he's cut....lol!

with that 200sx...with the computer going there some gas (some foot on pedal) and it thinking it got max boost wouldn't it just run like shit and sjut chew fuel cause she be running really rich alot which in most cases protects the engine....cause usally u tune cars leaner to get more power from standard fuel/timing maps!

02-01-2005, 06:41 AM
there is a twin turbo street driven mr2 with 2 VATN turbos ... i'll find links...

mechtech, aerocharger, vatn, mr2, Kurt Singer. 93T


pouya on mr2oc.com

02-01-2005, 09:12 PM
oy why would anyone spend that much money on a ca18et

det i guess i could understand but an et?