VNT turbochargers and control
Turbo Mini Forums

Hi there guys

Well ive decided to make a new thread rather than hijack the other one anymore!

The last car i built used a VNT 15 turbocharger -



As you can see i ended up adding an external wastegate to control the boost. I didnt have any of the sophisticated control that the golf it came off of had, i just plumbed it into the manifold. This meant that on partial throttle it was making 2psi, then i would floor it and the boost would dissapear as the vacuum dropped, and then it would come on boost proper.

I ended up using the mechanism to change the AR of the housing to suit my engine and driving, then locking the VNT off and used the wastegate to control the boost.

Well i now have another turbo -





Now i think im going to take a different approach with this one, i will use a normal boost actuator on the vnt mechanism. The VNT will be normally closed and boost will open it dropping lowering the backpressure and dropping the pressure.

Does anyone one else have any ideas? Has anyone else got a working VNT on their car/

Cheers

J

thght i'd stick the stuff from the other thread here for anyone searching.

can you give a description of how yours functions (do the vanes open with vacum?)


on the control side have you seen this site? there's some interesting boost control stuff where the vanes cycle each time the throttle closes to help with carbon build up.

http://www.thedodgegarage.com/turbo_vnt.html

Also some of the new vnt's have a electronic actuator, perhaps this could be controlled with megasquirt.

http://cgi.ebay.co.uk/RENAULT-ESPACE-3-0-d...tem190046428769

Edited by Joe C on 2nd Nov, 2006.

one thing that just occured is it may be worth running the actuator via a lever system so the sensitivity of the vanes can be adjusted as there sould be no wastegate "cracking" issues.

Hi,
The actuator on there is controlled by a solenoid valve fed from the vacuum pump on the diesel engines.
I don't think the putting a boost controlled actuator on there is going to give you the best results, as I think it needs to work the opposite way to a t2/3 exhaust wastegate.
If you could fit a vacuum pump and use the megasquirt boost table to control the solenoid, you could be on to a winner. After all I think the point of using the VTN is to get it spooled up faster...
Cheers,
Gavin :)

Edited by Bat on 2nd Nov, 2006.

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VNT vanes open and close causing the gas speed powering the turbine to change, opening them causes the gas speed to drop slowing the turbine etc.

As you say on a diesel the vanes are controlled using and ECU controlled solenoid and the vacuum pump on the engine.

I dont have this control, so my solution is to use the pressure from boost to open and close the vanes.
The T2/3 actuator will work in reverse causing the vanes to open as more boost is created, slowing the turbine, just as T2/3 wastegate works.

J

Hi,
I think you'll loose the bottom end torque that way as I think you need the vanmes in the same postition to get the quick spool up and limit boost.
I don't know if I'm right but I think as you go through the rev range the vanes need to be closed then open and then closed again.
Cheers,
Gavin :)

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i disagree about the vanes Bat,

I'm sure that you don't want the vanes closed to limit boost,

As I see it the vanes need to be fully closed at low speed until boost presure is reached and then slowly open as the speed (Exhaust flow) increases.

with a std actuator botched on I'm guessing the vanes might pulse open and shut, but on the other hand it may be ok.

also one thought i had was to reference the vanes to the TIP( ie the vanes close when the prssure in the exhaust manifold drops at low RMP) and then run a convetional external wastegate to control boost.

j , i think that would work well , its what i ws ging to do before i went the gt17 route , i imagine you have thuoght of this but you can also change the length of the arm to the vnt to change angular deflection per psi of boost ,and another thing i thought of ,was to put the diaphragm at something other than at a right angle to the arm , so that it would create a varying level of deflection per pound of boost ,and create a curve on the graph of mm /psi.
regards
robert

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

hi there is some vnt's that are using boost to control the vanes, just use the proper one on the vnt you have, ex renault espace 2.1 dt vnt, fiat croma tdi vnt, dodge 2.2 vnt..
cheers
fab

Fab,.... if you could take the pic of Vnts turbos to suit the A sreries engine

which would you go for ?

if money was not a problem
purchacing new

^^^^ LOL ^^^^^

well moneys been a problem for me dave at the mo..

i have spent up! for now

fabs the man

If money's a problem, maybe it's time to start selling the thirty+ 1275/turbo motors you have in storage! LOL!

Benross,
difficult to answer as this,
I would need a speced engine to answer correctly, boost, cr ,cam/revs, capacity, cyl head specs, exhaust manifold (mety one or custom) road race etc..
vnt have different sizes which are suitables for different levels of power,and also requirying different manifolding flanges an space.
the smaller being the vnt 15 as you can see on the upper picies, but it need a different actuator as many diesel engines uses vacum to control boost... also it have a small round inlet which make it difficult to use on std manifold, so need a custum one
his rate is 120/150 bhp max
my prefered vnt because they are t2/t25 flanged are the td25 type used on earlier vnt powered engines this is a derivation of the famous vnt 25 used on dodges 2.2, and being a brother it share with it the boosted actuator and t25 compressors from which we know maps and also on which we can bolt on any of the 25 comp wheel/housing so it can be fine tuned.This said t25 wheels are ok up to 2.0 pressure ratio (15psi's of boost) after this it start to decrease in the lower efficiency range and then it's better to use a gt vnt (ie gt 17/20v) a gt 2056v from fiat 2.4jtd( which was a td25/vnt 25 in the first ones) or audi 2.5 can sort over 200bhp without lag as a blower....... I can try to answer correctly and write a lot more but it will be a pain to read . tell me more about your engine , and sure I'll help as much as I can.
fabrice

about the imp,
I made a voyage around the net and if I'm correct it's at least one liter capacity, I'm scared that the previous vnt 15 was already lightly oversized, then a gt22..........you'll fail in surge as far as middle revs and then never go in the high efficiency operation
why did you want to change the vnt15?

yes it may be time dave ...lol!!

fab, i will pm you the spec:

not as though its .......... over the top for now!

thinking for the middle of next year, when i have got these home projects out of the way!!!!

you have got to keep the Wife Happy ...OH!!!

I'm understanding your point about your wife..............
you're welcome to enquiry when you'll need
cheers
fab

Hi fab,

I went for the VNT22 as i also have a supercharger on the engine. The turbocharger will see the engine as almost 2 litres, even though its only 930cc.

With the supercharger pushing upto 15psi of boost into the engine just off idle, the exhaust flow is increased substantially. This should enable a much larger turbocharger to be sustained.

I hope it works!

J

I took some times as I never look for this but if you engine see 15 psi and so blow them to your turbocharger , then how many do you want it to put on them? an other 15 psi? this turbo will well be geared by a 22 turbine wheel, but his compressor need to blow a small amout of air if 15 psi is allready supplied by the charger then you would need a smaller compressor as you'll be completely inefficienty if not under surge. Perhaps I missed something but you should substract from your compressor flow the charger flow, then you'll find the right flow/pressure
fab

a last question

did you though that the blown charge from the charger will blow thru the turbocharger compressor when this one will not be on boost and then will try to turn the turbine back. I think it's possible to shut the charger and then switch to turbo but not use the blown charge exhaust from the charger to spin a bigger turbo to blow on much pressure.
fab

no faB mon ami the turbo would be acting like my big turbo on the tvr , it would blow into the supercharger , like my big turbo blew into the small turbo , ,so its airflow must supply engine air flow times a bar ( very roughly put !),. :)
j this will work ... on the tvr i had 8 psi at 4000 from the holset ,now running the holset on its own with no small turbo to create boost (and therefore create more ex flow) , i have 7 psi at 5700!!! this was sort of expected thuogh and is part of the experiment..

regards robert

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

7psi at 5700! That must be interesting to drive but top marks robert for trying these things out!

tom.

yes,
missed that it could be compound and not in y,
well though you take the charge tru the turbo then into the charger, so no charge waste into turbo comp :),then the pressure are charging each over,
I looked at some maps you should end in the middle of the field that's great
cheers
fab

oh god tom , its such a slug lol, j , if you want to see the twin staged setup its on the tvr progress on show us yours section .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Right the system i am going to use goes like this -

Intake - supercharger - turbo - intercooler - engine

There is a bypass for the supercharger so as soon as the turbo starts to pull more air than the blower is supplying, it can bypass it and pull air straight from the intake.

This should create a smooth transition between supercharger and turbocharger . it will also mean that lag is banished and made a thing of the past!

The supercharger will be supplying 9psi, and the turbo will be set for about 15psi, but with a higher flow rate.

Robert, i didnt realise you has two turbochargers on the TVR! Is it set up sequentially of compound?

J