turbo boost control?

[RichieRocket]

Hey guys, please help me understand how the computer controls the boost pressure. I'm only talking STOCK tune for now. I read other threads about the torque demand throttle system and how max boost pressure can depend on air temperature, fuel octane, etc. Also, how the stock tune can learn out mods and pull back any power gains...

I was trying to explain this to a co-worker. He did some turbo tuning years ago on a Mitsu Eclipse and now owns a ~2005 Dodge Cunmmins turbo-deisel with some kind of boost controller. He keeps saying that the waste gate only opens as a fail-safe so the engine doesn't over-boost. The boost is only controlled by throttle.

The way I understood it, at full throttle, the computer will open the throttle plate, use the knock sensor to detect knock, and adjust ignition timing, VVT positions, fuel injection duty cycle, and turbo boost to get max torque for the RPM it is at.
The waste gate is always adjusting to keep the psi where the computer wants it(except at low rpms). As rpms increase, exhaust flow increases, so to maintain constant boost, the waste gate must dump more exhaust around the turbine.

Is the waste gate controlled by a fully mechanical actuator/diaphram system or is it electronically controlled?

Anyone have any diagrams or schematics of the control system? I searched the internet, but no luck...

Thanks

 

[ThatTmoGuy]

best i could find as far as a diagram. IIRC no one has attempted a manual boost controller and many have felt it would not be wise with such a computer controlled system.

 

[sx sonic]

I'm not sure what the exact contol stratagies are for our car but out wastegate is held closed by spring pressure and supplemented by vacuum pressre or defeated by positive pressure.

The diaphram that controls the wastegate is bolted to the turbo and has a line that connects to an ecm controlled solonoid. If I recall correctly that solonoid has an additional 2 lines plumbed into it one from the manifold, not sure about the other. If my memory is correct than that would mean we have a delta gate controlled waste gate, so depending on what the ecm sees it can hold the wastegate closed longer or oppose the spring pressure so it opens sooner.

I will have to look at it again to be more certain.

Diesels are vastly different that gas engines and can only loosely be compared when it comes to boost control. They don't require or often have a throttle (plate) and have a much narrorer operating range. So much so that dome TDI engines don't utilize a wastegate at all..

But as far as regulating boost by throttle, that would be less than ideal in many circumstances as power will have to be sacrificed to maintain boost. I can see it being incorporated into newer cars but it would take a secondary roll to boost control.

-tyler

 

[severous01]

these are almost identical to BMW turbos, and i'm very familiar with the setup. to be honest, it's almost an exact replica that BMW has been using for 6 years now

first, the solenoid is pulse width modulated, and has a full vacuum on one side. that's the system vacuum provided by either manifold vacuum and a reservoir, or a vacuum pump. not certain here as i havent looked into it.

second, the output on the solenoid goes directly to the wastegate controller diaphram. with PWM control, you can have anywhere from full vacuum to zero vacuum at any given time. it's nice to have as you can control boost quickly with very little lag.

the way it works is when the ecm detects the need for boost, the wastegate is closed. boost pressure builds to the requested amount, and the ecm will stage the solenoid to open the wastegate at whichever given interval requested. boost pressure is reduced, vacuum to the solenoid is maintained via the reservoir/manifold. the solenoid is quick, just like an injector, and can be staged with pulse width modulation (PWM), also like an injector.

there is also a diverter valve somewhere in the system which will open when the throttle is snapped shut. the diverter valve directs boost pressure back into the low pressure intake system (turbo inlet side). this is also controlled via PWM and has no vacuum lines as it just opens or closes to allow/disallow boost back into the filtered air low side of the turbo. this also reduced turbo lag, and reduced turbo noise, and prevents damage to the turbo blades on both the intake and exhaust sides. older cars have the diverter valve built into one of the pcv lines of the manifold, newer cars have the valve built into the turbo itself. i dont see anything on the turbo, so it's likely in the pcv system.

 

[CoHPhasor]

Your friend is high.

A wastegate isn't just on or off, it varies the opening to control boost.

There are several ways to control a wastegate, either mechanical(spring pressure), or mechanical(vacuum pressure).

Spring pressure is generally the failsafe.
Usually if vacuum pressure isn't working right it defaults to spring pressure.

Vacuum pressure is either mechanical vacuum (direct from the manifold), or electronically controlled through a solenoid.
(Most "boost controllers" are electronic, though some use mechanical boost controllers. (Generally a valve that restricts the amount of airflow))

When turbos hit max boost your RPM hasn't maxed out.
If your turbo continued to boost all the way to the top you would overboost and something would break.
Instead, the wastegate opens partially until it levels off around max boost.

The only time your wastegate is fully open is either when maxed out or you lift off the accelerator.
(So you don't go plummeting into the car in front of you even though you let off the gas.)

 

[Eric Smit]

Also, the diverter valve, or as is commonly called a bypass valve on this forum, is located on the turbo. You can see it on the side.


-Eric Smit

 

[RichieRocket]

Thanks for the info guys.
Yeah the waste gate is definitely not on/off, it's constantly adjusting the exhaust gas flow thru the turbine side, to maintian the desired boost from the compressor side.

IIRC, my old '89 Ford Probe GT, 2.2L, 12-valve, turbo, varied boost with RPM. In stock configuration, at low RPM, like ~2500 RPM, the max boost was 12 psi, then it tapered down to 9 psi by redline. So there must have been some kind of boost controller (mechanical or electronic) to taper off the boost.

 

[CoHPhasor]

Thanks for the info guys.
Yeah the waste gate is definitely not on/off, it's constantly adjusting the exhaust gas flow thru the turbine side, to maintian the desired boost from the compressor side.

IIRC, my old '89 Ford Probe GT, 2.2L, 12-valve, turbo, varied boost with RPM. In stock configuration, at low RPM, like ~2500 RPM, the max boost was 12 psi, then it tapered down to 9 psi by redline. So there must have been some kind of boost controller (mechanical or electronic) to taper off the boost.

That also comes down to load and cavitation.
The heavier the load, the more boost you make.

When the wastegate opens, if it's internal and not separated, the WG causes turbulence around the exhaust turbine.
(The Sonic is prone to this as the housing is silly)
Most Internally wastegated turbos get "divorced downpipes" when possible which divides the wastegate and turbine areas to make separate chambers.
Later down the pipe the tubings merge making for a much cleaner exit.

 

[Aj713]

What's the best plugs to use on the 1.4?

 

[Hulty]

What's the best plugs to use on the 1.4?

The OEM that are in it, gapped to .028.


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