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Old 4th August 2009, 14:13   #1
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Exclamation How ECU tunable are Variable Geometry Turbos

Apart from the benefit of newer spares (timing pulley, belt etc) and ECU software.

The Key thing which I noticed is the Turbo tuning done by them in this newer version of the ECU software.

The Turbo NOW starts it workout at 1200-1300 rpm and thats the key.

I noticed this in my parking area(Quieter) while trying to get out of office.

Last edited by tsk1979 : 5th August 2009 at 15:56. Reason: New thread
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Old 4th August 2009, 14:30   #2
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Originally Posted by dadu View Post
The Turbo NOW starts it workout at 1200-1300 rpm and thats the key.
Dadu, this is not exactly a 'tunable' parameter. It's not like I can choose to make the turbo 'cut-in' at 900 rpm or whatever!
Exhaust gas flow is required to achieve any change in air delivery of a turbocharger! Hence the very name: Exhaust Gas Turbocharger. Also, hence the VVT turbos! But there is a limit to when the turbo can spool sufficiently to deliver air pressure that makes a difference.

There's a miscommunication somewhere!
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Old 4th August 2009, 15:12   #3
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Originally Posted by anupmathur View Post
Dadu, this is not exactly a 'tunable' parameter. It's not like I can choose to make the turbo 'cut-in' at 900 rpm or whatever!
Exhaust gas flow is required to achieve any change in air delivery of a turbocharger! Hence the very name: Exhaust Gas Turbocharger. Also, hence the VVT turbos! But there is a limit to when the turbo can spool sufficiently to deliver air pressure that makes a difference.

There's a miscommunication somewhere!
The Variable Geometry Turbochargers (VGTs and VTTs) has "leafs" that can be adjusted to provide boost, depending on the exhaust gas flow (or so I understand). If it is so, and if the ECU controls the angle of the "leafs", then turbos can be tuned to respond at lower RPMs. It is the fixed geometry turbochargers that cannot be tuned.

Can somebody put some more light on this?
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Old 4th August 2009, 15:56   #4
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Originally Posted by unni.ak View Post
The Variable Geometry Turbochargers (VGTs and VTTs) has "leafs" that can be adjusted to provide boost, depending on the exhaust gas flow (or so I understand). If it is so, and if the ECU controls the angle of the "leafs", then turbos can be tuned to respond at lower RPMs. It is the fixed geometry turbochargers that cannot be tuned.

Can somebody put some more light on this?
Uni is right, that why its called VGT VNT VTT etc etc.

Just to keep it simple, Variable Turbo's have movable vanes which can direct exhaust flow onto the turbine blades. The vane angles are adjusted via an actuator controlled by the ECU throughout the engine's RPM range to optimize its behaviour.

So its unlike the fixed ones and can be manipulated
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Old 4th August 2009, 16:37   #5
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Quote:
Originally Posted by unni.ak View Post
The Variable Geometry Turbochargers (VGTs and VTTs) has "leafs" that can be adjusted to provide boost, depending on the exhaust gas flow (or so I understand). If it is so, and if the ECU controls the angle of the "leafs", then turbos can be tuned to respond at lower RPMs.
Point well understood!
However, please note that WORK needs to be done to get useful output from the turbocharger.
A certain mass flow and temperature of exhaust gases is required before any useful work can be done by the turbo.
It is not as simple as setting the vanes to a different angle and start getting useful boost at very low rpms!

Else there would never have been anything known as turbo lag!
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Old 4th August 2009, 16:51   #6
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Originally Posted by anupmathur View Post
Point well understood!
However, please note that WORK needs to be done to get useful output from the turbocharger.
A certain mass flow and temperature of exhaust gases is required before any useful work can be done by the turbo.
It is not as simple as setting the vanes to a different angle and start getting useful boost at very low rpms!

Else there would never have been anything known as turbo lag!
The sensors provide all the info required but actually it's as simple as controlling the angles of the vane to handle the boost at low rpm's.

When the vanes are at near closed position (which is also at the most optimum angle to hit the blades at low rpm's), a narrow passage is left which in turn accelerates the flow of gas towards the turbine blades, making them spin faster.

This closed position is optimized at low engine RPM speeds, generates pre-boost to negate the lag. The turbo lag for 2.2l is almost non-existent now or atleast I couldn't feel it.

Last edited by dadu : 4th August 2009 at 16:56.
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Old 4th August 2009, 20:29   #7
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Originally Posted by dadu View Post
The sensors provide all the info required but actually it's as simple as controlling the angles of the vane to handle the boost at low rpm's.
Can't say that this is correct.
It is to do with the available energy in the exhaust gases.
At low rpms (low BHPs) there is just not sufficient energy available in the exhaust gases to derive any useful output by way of waste heat recovery/extraction!
No amount of fiddling with vane pitch or nozzle rings is going to create energy!
There is a severe limitation at low rpms; hence all this ado about turbo lag and all manner of attempts to minimize its effects.
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Old 4th August 2009, 23:23   #8
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Originally Posted by anupmathur View Post
There is a severe limitation at low rpms; hence all this ado about turbo lag and all manner of attempts to minimize its effects.
Partly correct. But, I think, Bernouilli's mantra can still be tweaked to squeeze some turbo force even at low RPMs. Actually, I tend to think turbo effect is proportional to engine RPM, more rpm more turbo, less rpm less turbo, etc, never nil.

What limits is the usage of turbo. Imagine, there is some turbo at all RPMs and you are idling and turbo is spinning, creating +ve thrust. What a waste. Or, you are in a bumper to bumper traffic and your turbo kicks in at 900 rpm. Not good unless you are in a mission to avenge some previous scuffle with auto in front or you want to claim warranty on clutch

I think engine designers purposely do not switch on turbo at low RPMs as, boost, however small may be, will be too dangerous for the average driver on the road.

Makes sense?

-BJ
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Old 4th August 2009, 23:47   #9
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In my case, the turbo starts spooling with sound low muted swoosh right from the time i change from 1st to 2nd gear, This is with the lastest ecu code. I distintly remember getting a push around plus 1500 initially.. Now its more linear.. So they do have changed something in the latest code.

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I was asked today near Jehangir Hospital Chowk **Is this a petrol safari** at red light stop

Last edited by Rahulk76 : 4th August 2009 at 23:53.
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Old 5th August 2009, 08:29   #10
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Originally Posted by bj96 View Post
... Actually, I tend to think turbo effect is proportional to engine RPM, more rpm more turbo, less rpm less turbo, etc, never nil.
Couldn't be more wrong. Aren't you confusing belt driven superchargers with exhaust gas turbochargers?
The exhaust gas turbocharger needs heat energy more than just the rpm. That means the engine needs to be running at high BHP for the turbo to reach designed boost pressure.
You could rev an engine to reline in stationary condition. That will not take the turbo to anywhere near its designed air delivery, measured as boost pressure or as volumetric flow rate.

Quote:
Originally Posted by bj96 View Post
I think engine designers purposely do not switch on turbo at low RPMs as, boost, however small may be, will be too dangerous for the average driver on the road.
Makes sense?
Unfortunately, no, it does not make sense. Why not do some googling and acquire some valid information?
Fortunately we do not need to 'guess' too much these days. The answer, my friend, is blowing in the wind, as dear Bob Dylan would say!
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Old 5th August 2009, 10:50   #11
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If pete's chips can significantly alter the torque curve, I think even the manufacturer can do that. So its possible that the torque curve now is flatter with new software.
To give an example, the same engine in esteem and Gypsy has completely different torque and power curves!
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Old 5th August 2009, 11:11   #12
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Originally Posted by tsk1979 View Post
To give an example, the same engine in esteem and Gypsy has completely different torque and power curves!
Indeed, some amount of trade-off can be done for one parameter vs another.
But it remains a trade-off.
The Gypsy & Esteem example has more to it - the gear ratios and differential ratios. The trade-off here being fuel efficiency and top end whack.
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Old 5th August 2009, 11:16   #13
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Quote:
Originally Posted by anupmathur View Post
Indeed, some amount of trade-off can be done for one parameter vs another.
But it remains a trade-off.
The Gypsy & Esteem example has more to it - the gear ratios and differential ratios. The trade-off here being fuel efficiency and top end whack.
Exactly ! this is want I was thinking off. Can someone update about this?
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Old 5th August 2009, 11:45   #14
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JKD, no great details but the differences are in the intake manifold, the exhaust manifold and surely the ECU programming (different timings).
All of this still does not make the engine suitable for use in an SUV.
The gear ratios and the final drive ratios HAVE to be altered (from the Esteem aggregates) to achieve that status.
A very tractable set up, with lower redline, poorer FE but amazingly capable of doing what it was designed to do.

I'm sure there are experts here who'd furnish all the details, but on an appropriate thread!
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Old 5th August 2009, 14:33   #15
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Quote:
Originally Posted by tsk1979 View Post
If pete's chips can significantly alter the torque curve, I think even the manufacturer can do that. So its possible that the torque curve now is flatter with new software. ...
What Pete can do, a manufacturer necessarily can't. Manufacturer's are bound hand and feet by the conditions someone gives them. If GoI say be BS3 or BS4 compatible, some sacrifice has to be made on torque & angular acceleration (pick-up) for the sake of NOx, SOx and what not w.r.t. 'conditions anticipated' (avg. temperature, avg. pressure. fuel composition, duty cycle etc.).

The same engine is very well behaved with a curve (which is incidentally called the "driveability map") meant for Austria - that's where it was originally tested. Alas, the Indian curve peeves us Indians.

Pete's box doesn't change the map/curve, it only fingers 'conditions seen' - the ECU simply goes by that to calculate - per revolution - the quantity of fuel to be injected. It does not 'communicate' with the ECU CPU/ROM to make a difference. It only influences indirectly by making the ECU inject a smidgen more fuel, by making it think there is more oxygen available or the air temperature is less (for example). This is like advertisements change consumer behaviour, even though people use their own brains to take a purchase decision.

Quite likely no one with a Pete's box strictly monitors fuel consumption or even emissions. Common sense logic: if the driveability is better, everyone becomes a better driver and are more satisfied, and they don't push the vehicle like mad to make it work to their expectancy.
* Did it actually consume more fuel? Yes, for those short bursts it did
* Did it actually increase full-tank-to-full-tank mileage? Quite likely no. If done well, mileage will be same if not less, since the tendency to dwell in 2nd and 3rd is now less. Less mileage definitely if not done well
* Did it affect emissions (not smoke)? Quite likely yes, since when fuel injected does not match the homologated map, emissions take the hit

Anyhow, we first care about "driveability" - everything else is secondary. But, is a flatter torque curve what is desired, or torque curve matching gear ratios (which does not have a linear relationship) and "pick-up" expectancy? How much fun will it be if the "map" is driver-selectable to suit the duty cycle (city, highway, off-road) without compromising mileage, emission and other requirements!
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