[anupmathur]

Originally Posted by DerAlte

Intuitively (I can only do that) the effect of absolute values like calorific value etc. will be the same, when we are comparing efficiency at low load/rpm v/s high.

I should have said total calorific value.

OK, suppose we burn 10 gms fuel at low bhp and 1 gm gets wasted as heat energy.
At high bhp, suppose 100 gms fuel is burnt and 5 gms goes as waste heat.
The efficiency is higher at high bhp AND there is more heat energy in the exhaust gases.

[7600]

There are bits and pieces of information on this thread that make sense. Now, VGT's are designed to have a wider operating map to prevent compressor surge or choked flow. The vanes/nozzles are a way to widen the map and if the vanes is closed at low engine load (brake mean effective pressure) then the engine will produce more torque at a lower rpm. However, closing the vane causes the exhaust pressure upstream of the turbine to increase which also aids exhaust gas recirculation. Now EGR does in many ways, reduce NOx emissions and is most cases increase the ignition delay to allow for improved mixing of air and fuel.
Too much mixing of air and fuel causes high combustion temps/pressures leading to NO emissions while very low mixing (low ign delay) causes formation of carbonaceous particles or soot.

The vanes can definitely be remapped in the ECU to open/close. This will definitely play havoc to the combustion strategy that has been adopted. Now the fuel injection rpoessure, spray and cone angle of the injector are designed for operation under certain circumstances. If the boost pressure, temperature etc are altered, it could have an impact on fuel consumption, emissions and performance - positively or negatively depending upon how the systems interact!
Cheers!

[PRADEEP KUMAR]

Originally Posted by anupmathur

So where do we stand now, with respect to the above statement?
Is there or is there not the cure-all VGT?
Are there trade-offs that need to be made? Or is the ECU capable of deriving complete satisfaction from a VGT?

I'll never forgive M&M for the compromise they have sold to me, if such technology actually exists! Seems like only a re-programming of the ECU is required!

Folks,
At times ignorance is(was?) bliss!!
Sorry if OT.
Now after going through this thread i have more doubts than answers.
I have a 2.6 crde scorpio where the turbo blew up and got the entire core assembly replaced.
I had to personally go to the TEL outlet in chennai to do it.So the engineer there mentioned that this is a old TURBO and the new ones are the VGT types for which there is absolutely no way yet to service etc.The cost of old turbo for 2.6 crde is 14.9k.
Now the question is .By launching 2.2 L engines coupled with VGT has M&m COMPROMISED??
Is a 2,6 engine with old turbo set up better than the current one?
Gurus please , my head is bursting......
tnx

[jkdas]

Nice thread.

Originally Posted by Thomas8700

what all is going on over here??

VGT for Euro 3 in the safari?

then how is an FGT unit in the punto or ritz able to achieve Euro 4 ?

Originally Posted by anupmathur

OK, I'll give you a brief explanation.
Small little VGTs will spool up very fast and give usable boost from virtually idling rpm onwards. Then, even with the vanes FULL open, they'll fall woefully short of boost at higher BHP. Needless to say an exhaust gate will be MANDATORY to prevent absolute chaos due to the impossibly small total area available.
A larger VGT will fail to provide useful boost at low revs due to the inertia it possesses.

In short, the requirements are contradictory for boost at early rpms and for full bhp operation. A COMPROMISE is the only way out. Give some, gain some. Much like with suspensions and a lot of things in life! This is where art and engineering are merged, with experience.
There is no magic! There is no cure-all turbo available yet. And it will not be till someone re-writes the laws of Physics!

As for the kind request for relevant articles, I'd rather you Google than I! Sorry.

'

Chapter one: The basic theory of VGT

Originally Posted by ImmortalZ

With a normal turbo, you have to strike a balance between turbo lag and top end boost. A small turbo will spool up very fast, but will choke the engine at high RPM. However, a massive turbo needs high exhaust pressure to spool up, so it'll make no boost at low RPMs and is pretty much a big restriction in the intake and exhaust as far as the engine is concerned.

A way to imagine this is with a garden hose. Imagine that the rate of flow of water is constant. If you reduce the aperture of the hose with your thumb, the water will fall farther. However, when open the taps a bit and now, either your finger will have to be forced off to let the water through, or the hose pops off the tap.

A VGT is different in the sense that the finger in our example is ECU controlled and moveable. So at low RPM, with the exhaust pressure low, the vanes are moved so that the mouth is constricted (to be crude). As exhaust pressure builds up with RPM, the vanes are continually adjusted so you're always on boost and yet the turbo isn't limiting the flow of air.

However, it is still a turbocharger. It cannot make full pressure while at zero RPM, like an electric motor can. A VGT just widens the usable power band of a turbo charged engine.

Oh and Thomas is better served if he keeps quiet. We all know what happened to sameel.

Conclusion

Immor; Thomas can enlighten us without naming any manufacturer;

Originally Posted by dadu

VGT's provide for a wider band of service from low to higher RPM's, depending on the engine and its configuration. There is nothing called a cure all, but a better managed Turbo compared to Fixed Geometry ones.

It depends on the manufacturer, since 2.2l was a new engine with a VNT turbo, TM came up with a better handling of the VGT through the ECU upgrade.

My statement stands as is.

Chapter 2:

Originally Posted by anupmathur

SUV, the debate here is not whether VGTs are ECU tunable - they are.
The issue is slightly different - that there is only a limited range which even a VGT can address. The requirements for minimizing turbo lag and for full power boost are contradictory. Any turbo is therefore a 'compromise' and is ECU tuned to provide the best optimized solution, not the complete solution.

A more cpmplete solution could come from a combination of supercharger for low loads handing over to a turbo for high loads. But the cost of such a setup would be significantly higher.

The solution I presume.

Edit: to those who have doubts about 3 liter and 2.6 litre.

I GUESS, those engine were old and heavier. Better material and technology came in and hence they became obsolete.

Right?

[tsk1979]

I asked the engineer about this new firmware and performance change.
He laughed it off saying no changes in performance, its more like placebo effect.
This firmware was to fix the erroneous service light some customers were getting. There is no change in the torque curve or BHP map with this new firmware.
He told me that most people who had this firmware upgrade also had their normal service and other things done. Therefore the car seemed smoother and they attribute it to firmware change.
BTW he was aware of Team-bhp and showed interest in joining.

[amitk26]

Originally Posted by tsk1979

I asked the engineer about this new firmware and performance change.
He laughed it off saying no changes in performance, its more like placebo effect.
This firmware was to fix the erroneous service light some customers were getting. There is no change in the torque curve or BHP map with this new firmware.
He told me that most people who had this firmware upgrade also had their normal service and other things done. Therefore the car seemed smoother and they attribute it to firmware change.
BTW he was aware of Team-bhp and showed interest in joining.

So does he mean that all those service lights and related replacements was waste of money from TML as I suspected earlier on your thread and it was a software issue from the beginning ? Or did he say that to placate you and give some logical reason for service lights on your Safari ?

BTW the effect is not totally placebo there was a pronounced turbo kick at 1750+ RPM earlier which was there when I purchased and remained even after first service and an intermediate service and oil change but that has totally disappeared now after 2nd service and ECU flashing. Also they have also changed timing kit so may be that has an effect.

[tsk1979]

My service light issue went away with parts change. In some cases service light used to come and go randomly. Something like a false alarm. So ECU parameters were changes.
As for the kick you feel, the timing kit got changed, so that could be possible reason.

[anupmathur]

Originally Posted by PRADEEP KUMAR

....
Now the question is .By launching 2.2 L engines coupled with VGT has M&m COMPROMISED??
Is a 2,6 engine with old turbo set up better than the current one?

LOL, Pradeep, here are some ramblings that might help put things in perspective:

There are a lot of factors at work simultaneously.
There are social demands, there is technological innovation, there are political imperatives, there is the need for conservation and fuel economy and a host of other considerations.
What we see is a sort of net outcome influenced by these various factors, which change from decade to decade.

It could be correct to say that M&M has compromised with the 2.2 engine. Looked at from another perspective it would be foolish to say so! Everything is technologically superior. Everything has been done to strike a fine balance amongst all the requirements that have now entered the equation, and to stay competitive.

It is expedient that such change be accepted. Because the old practices were very much more wasteful and/or were not tenable or were just not sustainable.

Good or bad is dependent on what you expect from a product. If my priority is to be green, I should happily accept new technology. If that is not a consideration, why, I'll take the old gen three forward gears 6 ltr medium speed petrol engine with its adrenaline pumping torque characteristic and hardly any need for gear shifting! All Americans cars of yore were like this.

There is a certain beauty in simplicity. At the same time a lot of attributes are unacceptable today due to the various other imperatives. An old gen car, for example, cannot even be registered in most of our tier one cities. Pollution/emission norms have taken away that choice.

New tech is far more complex and there are dozens of sensors and controllers that must work in unison. Theoretically, it should not detract from the reliability of the machine, but practically, it invariably does. At the very least, it detracts from ease of troubleshooting and repair, which can hinder safe and complete enjoyment of a trip along a road less travelled.

And it does not necessarily mean that new technology does the particular job better, when viewed in isolation from other considerations. There is no choice but to make it conform to current legislation. Hence the compromises. A unified product that meets an ever growing and complex set of demands, as it were!

Is this bad? It would be very short sighted to say yes.

[DerAlte]

Originally Posted by anupmathur

I should have said total calorific value.
...

Mathur-sahab, sahasra dhanyavad! Fully underishtud. This was a pesky question that was outstanding in my mind for 33 years! Full 6th sem lab-ka viva yaad aa gaya!!!

Originally Posted by jkdas

... Thomas can enlighten us without naming any manufacturer; ...

Richtig! Even though the algorithms used by Safari's you-know-who and Thomachan's you-know-who are different, they wouldn't want notes to be compared in public. Now that calls for a meet, eh?

Originally Posted by tsk1979

I asked the engineer ... its more like placebo effect. ...

To be expected. One wouldn't think of reducing the turbo cut-in rpm drastically (with the same turbo) - the change involves ~1000hrs of testing on the dyno (performance + regression test), and then you go back to ARAI for re-certification.

Anyhow, if consumers are happy with the apparent performance boost, who's complaining?

[dadu]

Originally Posted by DerAlte

To be expected. One wouldn't think of reducing the turbo cut-in rpm drastically (with the same turbo) - the change involves ~1000hrs of testing on the dyno (performance + regression test), and then you go back to ARAI for re-certification.

Anyhow, if consumers are happy with the apparent performance boost, who's complaining?

Although , I have a strong feeling that this was not done to please existing customers after almost 2 yrs of launch. Its a learning from the New Safari which is in the offing with the same engine, currently under tests.

[PRADEEP KUMAR]

AnupJI,
I would strongly recommend you to take up Teaching in research set up!!
I was blown away by the reply.
TBHP is lucky to have people like you on board.
In fact i find this forum so enriching for petrol heads.
Keep up the good work,knowledge shared here is worth its weight in Gold.

[anupmathur]

LOL, Pradeep, thanks, but you're gushing!

[VeeTee]

Originally Posted by anupmathur

More precisely, it is a nozzle ring that controls the apertures and the angle of incidence of exh gases on to the vanes.

Anup,
I also know of VGTs (e.g. Cummins Engines) where the volume is controlled by moving the whole blade assembly. There is not control of the vanes or the apertures.

[anupmathur]

Originally Posted by VeeTee

I also know of VGTs (e.g. Cummins Engines) where the volume is controlled by moving the whole blade assembly. There is not control of the vanes or the apertures.

Satish, the whole blade assembly would, in effect, mean the whole rotor.
Could you please point me to an article/brochure?
I have never come across or read about the entire rotor being axially moved inside the turbo casing to control volume.

It would have to be a nozzle ring or sleeve of some sort. Or waste gates to let the exhaust bypass the turbo.

[7600]

Thats made by Holset..