Thread: Boost modulator/regulator

I asked the same question a few days ago.

Its better keeped on.

Consider the vnt option for constant boost.

Originally Posted by davrac

Doing some work on the disco td5 today and began to wonder. What is the real benefit of the turbo boost modulator and what would happen if I bypass it?

It controlled by the ECU and delays the opening of the wastegate on the turbo (through restricting the airflow through the vacum tube between the two) in order to increase your boost pressure at certain times.

Originally Posted by davrac

Hooked up the boost gauge a week or so ago an boost was fluctuating between 16 and 19 psi. I would prefer if the modulator would not adjust the boost and I could just know what the boost pressure is consistently.

Why is fluctuating a boost levels an issue? Even without it your gauge is not going to just read a constant boost level.

I'd suggest you go and read about how the turbo works as you've got quiet a strange statement in there. Perhaps start with this thread - http://www.aulro.com/afvb/discovery-...t-set-ups.html - although there are plenty of others and plenty discussing the modulator already.

Originally Posted by twr7cx

Why is fluctuating a boost levels an issue? Even without it your gauge is not going to just read a constant boost level.

I'd suggest you go and read about how the turbo works as you've got quiet a strange statement in there. Perhaps start with this thread - http://www.aulro.com/afvb/discovery-...t-set-ups.html .

Thanks twr7cx, I have read the posts previously writen and have a good understanding of how turbo's work. What is the strange statement?

I understand that I will never get a perfect reading or boost pressure as there are many contributing factors that make the boost fluctuate a little.

What I am saying is, is there any real benifit to keeping it there. From memory when I had the boost gauge on the modulator would open for a short time under full accel and about 18-19psi would be achieved. Whilst maintaining full accel the ecu would then manage the modulator and the boost would be controlled back to about the 15-16psi mark. Which is what the waste gate actuator spring is rated at from factory I think.

So....If by removing the modulator and fitting a manual bypass valve, the ecu would have no control over what pressure is going through the vacuum hose as you call it to the wastegate actuator. Thus maintaining a set boost pressure as such.

I understand the theory behind shortening the rod between the actuator and the wastegate(longer to open, higher initial boost etc) but this will never change the pressure rating of the spring in the actuator itself, which is why the modulator bleeds boost pressure off to stop the wastegate opening for a period which equals the higher boost until the modulator closes.

How are people lifting the boost on their Defenders without the modulator? Manual bleed valve or shortening of the rod? Just wondering.

Oh and just for the record, there is nothing wrong with the way my TD5 is running with the modulator in place, all is well, I was really just wondering why we have/leave it there. I understand why landrover put it there from factory, but not sure why we leave it there once we start wanting to adjust and maintain boost levels.

Thanks

Dave

Originally Posted by twr7cx

.

Oh and I noticed you live in Hobart, I am in Howrah, any chance I could have a look at your VNT setup sometime.

Cheers

Dave

Originally Posted by davrac

Oh and I noticed you live in Hobart, I am in Howrah, any chance I could have a look at your VNT setup sometime.

Sure Dave, any time. I'm off to Fiji for a fortnight at the end of this week though, so would need to be before or after...

I'm also in Howrah, so should be easy to setup. Suprised you haven't seen me around on the roads then:

Originally Posted by davrac

Thanks twr7cx, I have read the posts previously writen and have a good understanding of how turbo's work. What is the strange statement?

I found this to be a strange statement:

I would prefer if the modulator would not adjust the boost and I could just know what the boost pressure is consistently.

Does this mean that you are wishing your vehicle to have a constant boost level, i.e. always 16psi and never above or below?
Or does this mean that you believe that your reeding is not accurate as the modulator can change status and in doing so change the boost pressure?

Originally Posted by davrac

I understand that I will never get a perfect reading or boost pressure as there are many contributing factors that make the boost fluctuate a little.

Where have you plumbed your boost gauge in? What hose have you used for it?

Originally Posted by davrac

What I am saying is, is there any real benifit to keeping it there. From memory when I had the boost gauge on the modulator would open for a short time under full accel and about 18-19psi would be achieved. Whilst maintaining full accel the ecu would then manage the modulator and the boost would be controlled back to about the 15-16psi mark. Which is what the waste gate actuator spring is rated at from factory I think.

Yes, there is a benefit to keeping it there. It increases your boost pressure at certain parameters (I am unsure when the ECU uses it). The modulator blocks or restricts the boost pressure flow through the vacum line to the wastegates actuator. This results in the wastegate staying closed for longer thereby increasing the boost pressure (due to the turbo having more exhaust gas driving it).

If you remove the modulator you will find that your wastegate opens earlier and your boost therefore will not go as high - result is a loss of torque and power.

Originally Posted by davrac

So....If by removing the modulator and fitting a manual bypass valve, the ecu would have no control over what pressure is going through the vacuum hose as you call it to the wastegate actuator. Thus maintaining a set boost pressure as such.

You can safely remove your modulator and drive your vehicle. You will not cause any harm. Your fuel ratio's might be slightly out for your tuning, but that be minor. However you'll find that your turbo produces less boost and you'll have a loss of power and torque. I'm not sure why you'd want this.

You don't need a manual bypass valve. You can just run a single vacum hose from the steel pipe that is post-turbo but pre-intercooler to the wastegate actuator. This will bypass the modulator.

It won't result in a maintained set boost pressure. It'll lower your maximum boost level produced, but your boost pressure will still very based on rpm/fuel inputer (accelerator) etc.

Originally Posted by davrac

I understand the theory behind shortening the rod between the actuator and the wastegate(longer to open, higher initial boost etc) but this will never change the pressure rating of the spring in the actuator itself, which is why the modulator bleeds boost pressure off to stop the wastegate opening for a period which equals the higher boost until the modulator closes.

This is where you have some confusion on how the wastegate works.

There is a vacum line going from the air intake system (after the turbo charger, but before the intercooler) to the wastegates actuator.
On the Disco's the modulator sits in the middle of this line. On the Defender there is no modulator, just a straight line. On a vehicle like mine with the VNT also no modulator just straight hose.

What happens is the boost pressure travels through this line. It travels in the direction from the intake piping towards the wastegate actuator.

The boost pressure pushes on the diaphragm inside the wastegate actuator.

On vehicles with the modulator fitted, the ECU can activate the modulator which will stop or restrict the boost flow. When the boost flow is stopped or restricted it does not get through the modulator to push on the wastegate actuator.

There is a rod going from the wastegates actuator to the mechanical linkage that phyiscally opens the wastegate.

When the boost pressure pushing on the diaphragm inside the wastegates actuator reaches a certain level, it pushes it enough to move the rod.

When the rod moves it opens up the wastegate.

You can test this yourself on your vehicle by blowing air into the wastegate actuator and watching the rod move. Note if you use an aircompressor make sure you have the airflow restricted down as full flow will likely blow the diaphragm.

Now, if you shorten the connector rod the diaphragm will need to move even further before it actually starts to move the rod. In order for the diaphragm to move further, it needs more boost pressure, so the turbo keeps spinning up (because the wastegate is not opening) until it has enough boost pressure to push that diaphragm far enough to push the rod to open the wastegate. This is how both D2 and Defender TD5 owners increase there boost pressure regardless of the modulator.

If you lengthen the rod the opposite occurs. Less boost pressure is required to push the rod. So a lower peak boost pressure is seen as the wastegate opens earlier and bleeds the exhaust gas off (instead of using it to power the turbocharger).

Originally Posted by davrac

How are people lifting the boost on their Defenders without the modulator? Manual bleed valve or shortening of the rod? Just wondering.

Exactly the same way that the D2 TD5's are doing it. Adjusting the rod length is by far the easiest and most effective way. This will easily produce 18psi which is about the limit that most want to run before worrying about other issues that arise.

For both the D2 and Defender, you could alternatively increase your boost pressure by fitting a turbo boost controller (e.g. BOOST CONTROLLERS | Turbosmart International ) into the vacum line that goes to the wastegate actuator, but that would require more expense and hardware when the rod length adjustment is free...