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FF#20! Wastegate Adjustment

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Volvo Repair Database FF#20! Wastegate Adjustment

Post by matthew1 » Fri Nov 30, 2012 7:31 pm

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Wastegate Adjustment, A Closer Look

Wastegate adjustment may not be the most exciting topic when it comes to performance and power but it’s one of the most important base settings when it comes to boost development in a turbocharged engine. Improperly set, you’ll find even a tuned ECU brings in lethargic and tepid power. So let’s take a closer look at the unsung hero of boost management, the wastegate actuator!

The Wastegate Actuator

First let’s fully understand the wastegate actuator, how it works, and what it ultimately does. The wastegate actuator is metal can with a diaphragm in the middle of it that is crimped between the can halves. The diaphragm is also connected to a rod that exists one side of the wastegate actuator. On one side of the diaphragm is a spring and on the other a vacuum port where pressurized air is fed. As boost pressure rises and pressurized air is fed into the wastegate actuator, the pressure on the diaphragm increases and at some point will overcome the spring tension on the other side of the diaphragm and cause the rod to start moving. This rod is in turn connected to the wastegate arm on the turbo, as it moves the wastegate inside the turbo begins to open and exhaust gasses start to bypass the turbine. When this occurs, less exhaust gas is acting on the turbine and so consequently it slows down in its rotational speed. This reduced rotational speed is directly felt by the compressor wheel as well since the compressor wheel and turbine wheel are directly and mechanically connected to one another. The slow-down of the compressor wheel results in reduced boost pressure fed to the engine. This is the fundamentals of wastegate operation and boost control.

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Every wastegate actuator has a spring in it and that spring has a set amount of tension. If more boost is required then more tension is necessary to hold the wastegate closed until that boost pressure is reached. Without changing the spring, how can this be done? The answer is by adjusting the amount of pretension the spring has against the diaphragm. That is accomplished by the threaded adjustment on the end of the wastegate actuator rod. This adjustment allows for considerable changes in wastegate spring tension that is required for higher levels of boost as well as better early boost onset.

The Simple Early Years

Wastegate control in early turbocharged cars was as simple as you might imagine, a vacuum port on the intake manifold was plumbed to the wastegate actuator and when the boost pressure in the intake manifold was higher than the total spring tension in the actuator then the wastegate would start to open and hold boost at that preset level. It’s as simple as that.

A Job Done Two Different Ways

In later cars with more advanced electronic fuel injection, the ECU (engine computer) was put in charge of wastegate operation by virtue of a solenoid (an electrically controlled valve). In the 850 models with a BCS (boost control solenoid) the pressure normally fed to the wastegate actuator is instead bled off when the BCS is activated by the ECU. In later models (1998 and up) the TCV (turbo control valve) blocked boost pressure to the actuator when it was activated by the ECU. The have the same job but do it in different ways.

Graceful Fail

In both instances the BCS and TCV, are designed so that if the solenoid fails the system will by default feed pressure to the wastegate in all conditions, resulting in a car that will only create boost to what the base setting (adjustment) of the wastegate actuator is. The system is designed to “fail safe” and prevent potential over boosting that could damage the engine.

Boost for the General Public

With that said, the reason the base setting is so important is due to the nature of the ECU programming. The ECU will not start activating the BCS/TCV until after the first 1psi of boost is generated, in some models it doesn’t start boost control until after 2psi. Which means if the solenoid will not start blocking pressure to the wastegate actuator until over 2 psi, it will start to open and reduce boost pressure far before it is necessary. With factory wastegate actuator pretension commonly under or around 2 psi a condition exists where the boost is bled off inside the turbine housing before it is desirable to do so and early boost development is greatly diminished. This results in a very flat, slow responsive power production.

The Answer!

The short answer is to increase the base setting above the minimum TCV/BCS operation range. In most cases 3.2 psi is a good starting point but you can refer to our recommendations at ardtuning.com for your specific vehicle and setup. For many though you can go higher even still for added midrange performance and efficiency. My basic rule of thumb is as follows; increase wastegate actuator spring tension until you start to see slight overboost, then back off the adjustment until the overboost is gone. So if you’re ECU is set to 10psi, when you start seeing consistent 11-12psi overshoot, go back a touch on the adjustment until the overshoot is gone. This is the most precise method since each actuator will vary some with regard to the spring tension internally since they age differently and the heat cycles from the turbo can harden the spring in some cases.

An Added Thought

With regard to overshoot I’m referring to on throttle, sustained boost levels. It is not to be confused with the normal and acceptable boost pressure surge between shifts, specifically with automatic transmissions. So don’t let that confuse you!


Robert Lucky Arnold
ARDtuning.com

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Re: FF#20! Wastegate Adjustment

Post by timmyc » Mon Dec 03, 2012 10:04 pm

I finally got my LPT car back on the road and would like to measure the boost. What kind of tool is used to measure boost and where does one acquire one?


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Re: FF#20! Wastegate Adjustment

Post by matthew1 » Tue Dec 04, 2012 10:50 am

You need a boost gauge. I bought mine from iPD (sponsor banner at page top), but any type will work. Like anything in life, generally the more you spend the more you get.

Boost gauge install basics
Boost gauge mounted in headliner

Your LPT might be different, but the concepts are universally identical.


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Re: FF#20! Wastegate Adjustment

Post by timmyc » Tue Dec 04, 2012 8:07 pm

Isn't there a tool to measure the amount of boost that I can use instead of installing a gauge? Is it a "set it and forget it" type of adjustment? I just wonder if it is necessary to have the gauge.

Thanks, Matt!


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Re: FF#20! Wastegate Adjustment

Post by ARD-Lucky » Wed Dec 05, 2012 9:42 am

Aside from a gauge I'm not sure what you would use to measure boost. although any pressure gauge will work especially if it's just temporary. Once the wastegate is set properly then you typically don't have to touch it again unless mods require a re-adjustment. For the most part it's as you say, set it and forget it :)



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Re: FF#20! Wastegate Adjustment

Post by timmyc » Wed Dec 05, 2012 12:34 pm

Thanks, Lucky. Good to know.

Would you be able to let me know the proper psi. setting? I am looking to get a white tune from you when funds become available (after the holidays).


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Re: FF#20! Wastegate Adjustment

Post by ARD-Lucky » Thu Dec 06, 2012 5:52 pm

If you plan on running the White tune then wastegate setting should be set at 4psi. Granted the White tune is intended for cars using aftermarket boost management like an MBC or EBC so wategate setting isn't as critical but should still be over 3 psi at least to start.



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Re: FF#20! Wastegate Adjustment

Post by hausmeister » Sun Jun 04, 2017 2:56 am

Kind of reviving this topic. I have a question regarding travel of the stock actuator. Or generally what would be considered a good actuator for a volvo. I cannot seem to find any reliable info on that (travel vs pressure)
I have an unknown old actuator and a Mamba I bought from ebay. I had some troubles with surges/overshoot when increasing the tension on the old one. I measured the travel - see picture (bottom). Is the old one still good? there is very little travel. New one seems very linear.
(numbers indicate psi, 1inch caliper for reference)
I can put a stiffer spring in the new one, but that only starts around 8psi which seems way too much. the current spring seems a bit too weak. I will play arouind a bit with it. I still have an ARD actuator, but that was way too stiff when I tried it before. I also relocated the bcs and shortened the hoses, that might help a bit.
IMG_20170604_104928.jpg
IMG_20170604_104928.jpg (96.58 KiB) Viewed 3296 times


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