[d3mon]

I have a Figo Aspire 1.5 TDCi, with a single channel Dieseltronic box.
While that does work great and gives me about 120 BHP, 270NM, can we really ever have enough power?

Quick background about the boost control strategy in the Aspire:

1) 3 Port Electronic boost controller (Boost solenoid)


This guy directly drives the wastegate, by bleeding off excess pressure as required back to the Air intake box. While it's bleeding off excess pressure, it avoids the wastegate opening up while the turbo is still spooling up. After it has spooled up, it will direct more of the air towards the wastegate, hence forcing it open.

It has 3 tubes, connected to

- Air filter box (for bleeding off excess pressure from the intake manifold, to aid spool up time. This is the reason why the Figo has super low lag)

- Intake manifold (To get the boost pressure)

- Turbo Wastegate (To actually open the wastegate and limit peak boost)

2) Spring loaded Wastegate

This is driven by the aforementioned boost solenoid and diverts exhaust gases away from the Turbo, directly into the exhaust, hence limiting the peak boost.

So the obvious next step in turning the performance up a notch is to increase the boost pressure. In the absence of a dual channel box, the following options exist for me:

1) Manual boost controller

This can replace the Electronic boost controller and directly control the wastegate, but it seems that these things are too unreliable and can be hard to tune. The possibility of getting a fault is also extremely high. So I have pretty much ditched this idea.

2) Wastegate Preload adjustment

The wastegate has a mechanical adjustment, that can allow the wastegate to open a little later, by turning the wastegate rod by a couple of mm. This option is still on the table and I'd like inputs on whether this is a good idea or not.

3) Disconnect the tube that goes from the boost solenoid to the Air filter box

Along with this, we should seal the hole in the Air filter box to avoid dust particles getting in.
Very important: Do not block the output from the boost solenoid - this will basically stop the boost solenoid from functioning at all, and can lead to a reduction in turbo boost built up.

Now this will basically allow the solenoid to vent directly to the atmosphere, instead of recirculating back to the air filter. What does this do? Well, a couple of things:
- The MAF starts reading a little more, since there's unaccounted airflow in the system. It can cause the car to run a little rich, but this is not a problem for diesels.
- The boost solenoid ends up diverting more air to the port meant for the air filter box, since venting to atmosphere (1 bar) is easier than venting to a boosted air box (up to 2.5 bar absolute pressure)

The effect of both of these is a little bit like a dual channel tuning box

The pipe to be disconnected is shown in the figure above, marked in red and yellow.

Anyway, I put my brave pants on, and actually disconnected the pipe. The engine started up just fine, and I went for a quick drive with the OBD II reader set to display the boost pressure and the MAF values.
What I observed from this quick spin was

- Revving in idle increased the peak boost from ~16 to 19 psi
- First gear peak boost was up by a couple of psi (I think I saw 20psi vs 18psi before)
- Second gear peak boost was up by a psi or so (22.9 vs 22)
- Third gear and onwards, the peak boost remained the same (23.8psi)
- Peak MAF reading went up a couple of g/s (equating to about 2.5 BHP)

Now all of this seems too good to be true, since it directly attacks the boost limiters that Ford has put in for the first & second gears, while not increasing the peak boost (hence avoiding a check engine light). But to be honest, I haven't finished all my measurements yet. Before I do that, I wanted to get a feel of whether what I'm doing actually makes any sense from a technical perspective or not.

Thoughts? Anybody want to give this a shot on their car and confirm my measurements?

Disclaimer: Please treat all of the information above with a pinch of salt, as this is my understanding and can be incorrect. I'm not responsible if you end up killing a polar bear while trying this out.

[Pranay J Pandya]

Air filter box (for bleeding off excess pressure from the intake manifold, to aid spool up time. This is the reason why the Figo has super low lag)

if true, then you should now see more turbo lag than before? what are your findings?

The volume of air being diverted to the waste gate is negligible when compared to the volume of air that is ingested by the engine. It is merely a signal of sorts for the waste gate. Just take a look at the size of the pipes that are used to connect the waste gate & solenoid, they are not very big in diameter are they? Expecting a difference in spool from it would be similar to blowing through a straw at the back of a table fan and hoping for more breeze on the other side


Let's step back and think of how boost is controlled on a turbo charger using an internal wastegate.

A waste gate controls the amount of boost pressure created by the turbo by altering the flow of exhaust gases sent to the turbine of the turbo charger. If the boost level is under the set target, then the waste gate valve remains closed and all of the gases are sent to the turbine. If the boost reaches the desired level, then the waste gate valve begins to open up thus, diverting exhaust gases directly in to the exhaust instead of the turbine section of the turbo charger. In this way, the speed at which the turbine spins and effectively how much boost is created by the turbo, is controlled by how much the waste gate valve is opened / closed.

Now, what controls the internal waste gate valve? The waste gate actuator.
What is the waste gate actuator? It is simply a spring loaded diaphragm attached to a rod (internal waste gate), the other end of which is connected to the internal waste gate flapper on the turbine side of the turbo. The spring contained in the actuator determines at what pressure the diaphragm moves. The diaphragm will be pressurized by the compressor side of the turbo and depending on operating conditions may see vacuum (idle) or boost. Stiffer the spring, the more boost pressure it will take to open the waste gate. Softer the spring, the less boost pressure it will take to open the waste gate. On adjustable internal waste gates one can also adjust the preload of the spring to adjust boost levels as you have mentioned.

A 3 port solenoid can you help you create more boost. How? By bleeding off the pressure that is seen by the waste gate actuator. Effectively, getting the waste gate valve open later than it would with just the waste gate spring alone. Higher the amount of air bled by the solenoid = later opening of the waste gate = more boost. But there's a limit to this which I will not get in to now.

To keep the solenoid functioning properly, it must stay free of dirt and blockages. This is the reason why the port that bleeds air is connected just behind the air filter. Doing this allows the entire loop to remain sealed and free from dirt.

From my understanding, disconnecting the bleed pipe from the airfilter tract should have no difference or very negligible difference on how much boost is produced by the turbo charger.

If you want to get more boost, then you must bleed more air from the solenoid, which can be achieved by using the dual channel controller or getting a remap. Of course, you could always fiddle with a manual boost controller or adjust the waste gate spring but being a closed loop system the ECU will keep trying to correct the boost level to what is programmed in.

[Jaggu]

Pranay has explained it well, even i don't think disconnecting the bleed pipe is a good idea or giving you major difference in performance. If you want to make a real difference, i would suggest changing the waste gate opening marginally and adding a better flowing (than stock) air filter system.

To go even wilder effect, try remap and a manual boost controller

Very nice DIY though.

[d3mon]

Originally Posted by Pranay J Pandya

Expecting a difference in spool from it would be similar to blowing through a straw at the back of a table fan and hoping for more breeze on the other side

I'm not suggesting that the spool time is different because of the sheer volume of air flowing through these tiny tubes. But, by letting the air escape from here, the wastegate doesn't see any pressure and hence doesn't start to creep open, while the boost is building up. Hence the ECU can delay the opening of the wastegate, unlike in a system with a purely mechanically coupled wastegate. In fact, this is exactly what you say later in your post!
Does that explanation hold boost..errr water?

Originally Posted by Pranay J Pandya

From my understanding, disconnecting the bleed pipe from the airfilter tract should have no difference or very negligible difference on how much boost is produced by the turbo charger.

If you want to get more boost, then you must bleed more air from the solenoid, which can be achieved by using the dual channel controller or getting a remap. Of course, you could always fiddle with a manual boost controller or adjust the waste gate spring but being a closed loop system the ECU will keep trying to correct the boost level to what is programmed in.

I agree. The difference in boost may be mostly transient, as the ECU employs a closed loop mechanism for boost control. So the best case scenario here would be boost spikes in lower gears, that are still safe, as they're under the peak boost in higher gears. We'll see.

[Pranay J Pandya]

Originally Posted by d3mon

I'm not suggesting that the spool time is different because of the sheer volume of air flowing through these tiny tubes. But, by letting the air escape from here, the wastegate doesn't see any pressure and hence doesn't start to creep open, while the boost is building up. Hence the ECU can delay the opening of the wastegate, unlike in a system with a purely mechanically coupled wastegate. In fact, this is exactly what you say later in your post!
Does that explanation hold boost..errr water?

My bad, when I initially read your first post it came across to me that you were suggesting the low lag was because of the re-circulation of air that was bled from the solenoid in to the intake tract

Your understanding of how the solenoid can be used to delay the opening of the waste gate to aid spooling time is correct.

Originally Posted by d3mon

I agree. The difference in boost may be mostly transient, as the ECU employs a closed loop mechanism for boost control. So the best case scenario here would be boost spikes in lower gears, that are still safe, as they're under the peak boost in higher gears. We'll see.

How about giving this a shot, take a look at the boost level across the entire rpm band say in 1st and then 2nd rather than just the peak value? What story does it tell?