VNT turbo's
Turbo Mini Forums

I just came across this, theres some nice internal VNT shots.

http://www.houlster.com/amigo/turbo2/index.htm

I remember mikemph was rigging up a VNT turbo, did this ever run? hw did it cope with the heat?

vnt turbos won't cope with very high temps and also with fuell deposit on the vanes: yes but,
that's for FACTORY production cars with thousands of miles RELIABILITY (tdis can make 170000 km with no turbo problems....), makes prevents complains from customers.
but we are in an other case , sure vnt's will blow your door for less than 150000 km's but will youb really make all of these?
for myself, vnt's are great and I only make 4/5000 km's with my mini by years , so if I only change the turbo every three years that's fine , so I will change for the new turbo technology :)

Thats pretty much what I was thinking Fab,

with my install being a crossflow it should be pretty easy to swap the turbo for a std spare if it did go bad.

Hopefully with them in mass production now they'll start to be available for a resonable price.

My main worry is the heat, for our applications we are likly to be looking at around 1-1.5 bar boost, which will put a lot of heat into the turbine. Although a VNT may survive on a larger engine with around 10 psi boost, 15psi upwards may be a bit different, although 2/3 years life is ok i reckon.

diesel engines are already blown to 15 or more boost, the dodge's were ok at low boost, I think you'll make more power with less boost on a vnt turbine as it will not restrict exhaust flow (on a well made with 15psi ..180+ bhp.), but with a cross flow head it will be sufficient to grenade traini's, drops and dif........I would be more worring about gears than the turbo :), don't choose a turbo that is to short for that kind of power you need a large turbine whell (the tdi 110 is too small, I would go for a vnt 2.5, 2.8 , 3.0 engine " fiat jtd 2.4" """could""" be good )
cheers
fab

Thanks fab, interesting stuff

mainly the crossflow head is to get around injection issues, rather than to make more power (although that will be a rather nice side effect )

I get what you are saying about having a large vnt turbo, there seem to be some about from the 2.5-3 litre espaces I was thinking that these would be too big, but perhaps not.

obviously the gearbox will need to be all out to cope with this, and hopefully Turbo Daves clutch setup will appear at some stage. the plan is to start at 10 psi boost initialy and work up to around a bar and see what the torque and power is like.

I cant see how an engine boosted to same pressure will make a significant amount more Hp when using a VNT. At the end of the day the turbo is extracting energy it requires from the exhaust gasses. The amount of extracted energy will be similar on both turbos as the work it has to do is the same, i.e. supply 10lbs of boost. The amount of energy the turbo extracts from the exhaust gasses is propotional to the pressure drop and flow over the the turbine and this would be proportional to the back pressure on the engine. I can possibly see it being better when running off power around time. The VNT just allows the turbo to be more flexible with a wider performance envelope for any particular turbine.

Don't get me wrong, VNT is good technology and as a whole the system may be better with a flatter and potentially wider power curve, but the headline figure would be very similar.

Edited by Mirage on 3rd Sep, 2006.

I was thinking that as the VNT would be operating at a higher efficency (The AR varies to keep the exhaust closer to its most efficient point?) so less heat would be generated and transfered to the intake, also there would be less back pressure due to being able to run a higher exhaust AR without loss of bottom end.

nicely put mini13

Edited by robert on 3rd Sep, 2006.

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

The VNT improves low down boost by making the nozzle smaller at lower revs. This ups the velocity of the exhaust gas hitting the turbine and spins it faster.

Must create a bit more back pressure at lower revs but this is offset by higher low down torque.

So at low revs it creates more potential energy between cylinder and turbine by upping the exhaust pressure. This is then converted into higher kinetic energy at the nozzle outlet which the turbine translates into higher speed.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

thanks robert,

i'm no expert but as axel points out there may be higher back pressure low down, but there is also more boost, ie more torque.

with out compressor maps for the VNT all i can do is make a "guess" but i think its reasonable to assume that we should be able to get the top end performance of something like a gt25 with thew bottom end of a gt15. Also if a FAB says the diesels running highish boosts they should hopefully be more eficient at htese higher boost levels.

I'm not disagreeing that overall the VNT would give a certain amount extra power at most revs but it may not give you a higher maximum power. If you optimised a standard style turbo for a certain power output lets say 150bhp at a given engine speed and a vnt made for the same. I don’t think you would see much of a difference when the engine was operating at this power/rpm range. Both setups with similar back pressure etc.

However as the VNT can retune it's self either side of this sweet spot you would get some extra power due to the decreased back pressures. I wouldn't think the difference here would not be huge though.

In the real world normal turbo ARs are biased towards smaller flow rates to combat lag, the excess gas and thus back pressure being bled away through the waste gate. With this kind of real world setup the VNT is going to give you a bit more power at max out put but I’d be amazed if it was more than a few percent. You could compensate with a fraction more boost pressure.

Road car technology is driven by ever tightening emission regs so an overall improvement of a few percent is great but to us dose it make that much of a difference?

Has anyone done any serious miles with one to see how they survive?

The heat in your inlet charge as it leaves the compressor is primarily a result of compressing the air and the efficiency of the compressor to turn the kinetic energy into flow at a given pressure.

Your right I think any benifit from back pressure related gains may be small but should be there,

Assuming the exhaust turbine is going its job more efficiently there should be less energy wasted as heat, meaning (as the inlet and exhaust turbines are thermally coupled) less heat should find its way into the inlet charge, take into account that this is happening over the whole rev range overall there should be a worthwhile but small gain.

the real gain will hopefully be in being able to use an AR geared toward making maximum power. What size exhaust housing does Mini Williams use?

Also shouldn't the back pressure stay roughly the same throughout the revrange?

in fact that's not so....simple,and my apologies for this at anyone would be touched.
the max hp's need a highflow turbine, with a diameter in relationship with his power output,and this is very important, generally you see comp maps topics and troubles, but the turbine side is as important, tehn you understand why garrett now rate their new range on turbine side :gt 15/17/20/22/25 which is just the turbine diameter etc with related power, then you match on this the best comp map and a/r permeability....complex , yes really ,even after a decade of readings, understandings, tries and calcs, I'm still learning every days...
ex: a cossie use a T3 with a middle a/r to sort good power mixed with drivability , little lag etc , but it is mooved by a large capacity engine..... apply the same power on a 1275....to be really efficient you would need the same turbine!!!!!! do you see the sort of lag and hassle it would be to drive, so hybrids tried to overcome this by using little turbine wheel with a larger a/r and larger comp wheel...but this was just "better" than the tinier drivable turbo; vnt allow the bigger turbine wheel to be driven by a lower capacity engine.
so:agree with mirage :it doesn't change the real dyno max hp, but you simply couldn't drive it mith a waste gated turbo really efficient on the turbine side (note on this :the garret gt range seem to have made a lot of evolution on this side)