DublinOh

I know that DV valves bleed off excess boost...and waste gates also release excess boost and are adjustable...but how does an ECU or flash control boost? Why does a 1 Bar flash need a waste gate adjustment? Hope this isn't a stupid question? Any info would be appreciated.

calturbo

A Wastegate is simply a turbine bypass valve. It works by diverting some portion of the exhaust gas around, instead of through, the turbine. This limits the amount of power that the turbine can deliver to the compressor, thereby limiting the turbo speed and boost level that the compressor provides.

The Wastegate valve can be "internal" or "external". For internal Wastegates, the valve itself is integrated into the turbine housing and is opened by a turbo-mounted boost-referenced actuator.
An external Wastegate is a self-contained valve and actuator unit that is completely separate from the turbocharger.
In either case, the actuator is calibrated (or set electronically with an electronic boost controller) by internal spring pressure to begin opening the Wastegate valve at a predetermined boost level.
When this boost level is reached, the valve will open and begin to bypass exhaust gas, preventing boost from increasing.

A Blow Off Valve (BOV) is a valve that is mounted on the intake pipe after the turbo but before the throttle body. A BOV's purpose is to prevent compressor surge. When the throttle valve is closed, the vacuum generated in the intake manifold acts on the actuator to open the valve, venting boost pressure in order to keep the compressor out of surge.
Bypass valves are also referred to as compressor bypass valves, anti-surge valves, or recirculating valves. The bypass valve serves the same function as a BOV, but recirculates the vented air back to the compressor inlet, rather than to the atmosphere as with a BOV.



Adjusting the boost is straightforward. However, it depends on the type of boost controller.

For a standard Wastegates actuator, simply recalibrate the actuator to open (more or less) for a given pressure. Changing the length of the rod that attaches to the Wastegates lever accomplishes this adjustment.
For mechanical boost control systems, adjustments may involve changing the setting on a regulator valve(s).
For electronic boost control systems, adjustments may need to be made to the vehicle's engine management system.
For an external Wastegates, adjusting the boost often requires turning the adjustment screw (when equipped) to increase/decrease spring load, changing Wastegates springs, or shimming Wastegates springs.

wross996tt

Cal, good fundamental descriptions. I will add specifically for our turbos (not in general):

Diverter valves (recirculating air valve) release boost pressure accumulated between the turbo and throttle body when the throttle plate is suddenly closed. The excess boost is plumbed back into the intake stream, helping to promote more rapid spool-up when the throttle is re-applied (hence not blow off valves as the pressure is not released to the atmosphere).

A Wastegate (bypass flap) controls the amount of exhaust gas that flows to the turbo. The wastegate receives a vacuum/boost signal from the manifold and bypasses exhaust gas from the exhaust manifold to the exhaust downpipe at a given PSI. The wastegate quickly opens and closes so that the turbo produces the required boost level.

The ECU can control turbo boost by using a pulse width modulated output wired to a solenoid. This solenoid is plumbed between the intake manifold and a wastegate. Keep in mind that the ECU does not directly control the wastegate. It manipulates the operation of a mechanical system. If an improper component is being used – maybe the wastegate spring is grossly over or undersized - the ECU may not have full control over boost. The reason most folks upgrade the wastegates is to get the stronger springs to prevent pre-mature opening. Also the reason some folks go with a GReedy boost controller as it allows more direct control of the operation.


Also remember boost without fuel equals no power. To make power you need both...so as you increase boost you will reach limits of efficiency...due to temperature (volumetric efficiency) and fuel delivery. So now you can understand why larger turbos can handle more boost and still make power (larger volumetric efficiency) and why at some point you have to upgrade the fuel delivery (injectors/rails/FPR) so as not to starve the engine.

Cheers

DublinOh

Wow guys...thanks for the detailed explaination.....and yes, cheers to you both

John D II

wross,

I'm not sure about the recirculating DV promoting more rapid spool of the turbos. Here is a post from someone at FORGE VALVES that states it does not have any effect on turbo spooling at all - Anyhow, it's an interesting write-up about DV's and BOV's...

Mike@Forge Jul 3, 2006, 08:15 PM
I'll try to be as clear as possible in my explanation of things and I have simplified a few areas for ease of understanding, but I will gladly elaborate if necessary. The points I touch on will be those that are most commonly brought up on these and other forums, but other relevant information is included for everyone to consider.

The basics.

What a Diverter/Blow-Off/Bypass Valve is and what it Does:

There are numerous names given to this part, and it should be understood that they are all interchangeable terms used in different ways by different people all to describe the same basic thing.

Diverter Valve
Blow-Off Valve
Dump Valve
(Compressor) Bypass Valve
Pop-Off Valve
Discharge Valve
Boost Valve
Hooter Valve (Yes, I have even seen people call them "hooter" valves )
Etc.

Whether the valve is venting or recirculating, it is still a “bypass valve”, and since this term gives no implication to recirculating or venting function, it is the best term to use when talking about all of these valves in general terminology.

Basically, a bypass valve exists to relieve a residual amount of boost pressure in a pressurized application when the throttle on the application is abruptly closed preventing the air from “backing up” into the compressor wheel of the turbo, slowing it down, thus creating “lag” when the throttle is reapplied.

Whether the air is vented or recirculated makes NO difference to the amount of “lag” created.

"Lag" would only be created if there was no bypass valve in place at all, and the residual charge air inside the intercooler piping "backed up" into the compressor wheel at throttle lift. Whether an atmospheric or a recirculating valve is used, the valve is still able to bypass the residual charge pressure at throttle lift allowing the compressor wheel to maintain it's rate of speed, thus reducing “lag”.

Aftermarket Valves:

Options abound. That's all really.

There are so many choices available on the market, it's perfectly understandable how people get confused, so let's be sure to take it easy on the "newbies" to the turbo world who need some guidance. We were all there once too.

With that said, valve selection IS a very important thing and should not be taken lightly. Valve selection should be made considering a number of different factors each of which will be specific to the application it will be used on and the use the valve will see.

Design
Boost Holding Capacity
Flow Volume
Adjustment Range
Quality
Reliability
After-Sale Support
Etc.

One VERY important factor is atmospheric vs. recirculating, and while I will elaborate on this more in depth below, if anyone is not comfortable making the decision themselves, please consult with a reputable and trusted valve manufacturer or your vehicle's tuner before making your choice.

ATMOSPHERIC vs. RECIRCULATING vs. 50/50:

The BIG question.

The simple answer:

What kind of valve is your engine management system designed for and/or capable of allowing for the use of?

Yes, I answered a question with another question, but the real answer is, there is no simple answer. Each person will need to consider what their plans for their car are, what type of engine management system they will ultimately be using, and what valve can or can't be used with that type of system. “Blow-off valve sound” aside.

Firstly, we need to know what type of engine management can use what type of valve.

Mass AirFlow systems are designed as "closed-loop" systems requiring the use of a recirculating valve.

Speed Density systems are typically setup as closed-loop systems from the factory, but they can typically use either a recirculating OR atmospheric valve without any major detriment to the system.

MAP based systems (manifold absolute pressure) are typically capable of allowing for the use of either valve as well, but most MAP-based systems are fully stand-alone and require significant tuning to overcome any changes.

Now, with that said, the OEM ECU used on the Evo is a Mass Airflow system. It requires the use of a recirculating valve. If anyone, through the course of modifying their car, plans to continue to use the OEM ECU as the base for their engine management (even if some aftermarket tuner has uploaded new programming or a piggyback system is used), it is HIGHLY recommended to continue to use a recirculating valve.

The use of an atmospheric valve will cause a rich fuel mixture due to the loss of already metered air which the ECU is expecting to remain in the system. When the air is vented, the ECU dumps fuel into the system expecting the air to be there, and it's not. This rich fuel condition can sometimes be severe enough that the ECU cannot compensate for the condition and the car will run rough, not idle properly, experience a loss of power, and also experience poor fuel economy.

I have personally seen, on my own vehicle, a loss of as much as roughly 40 miles per full tank of fuel from using an atmospheric valve on a tuned, but otherwise stock engine management system.

If anyone, through the course of modifying their car, plans to switch their engine management from the OEM ECU to some form of standalone engine management (NOT a piggyback system, as even a piggyback still uses the OEM ECU), they can then, and only then, consider the use of an atmospheric valve, as such a system can compensate for, or be tuned to allow for the use of such a valve without any of the problems mentioned above.

50/50 valves, while seemingly great, are not an ideal solution by any measure, in my personal opinion.

(Yes, everything below is a personal opinion and subject to argument, but I’d like to think I know what I’m talking about.)

While they are designed to accomodate those with the desire for an increase in the "blow-off valve sound" from their car, they do so in a way that is still venting metered air, still causing a somewhat richer fuel condition, and still potentially leading to the above mentioned problems. While they may appear to work on any given vehicle, they are only doing so within a window that is not yet necessarily a largely detrimental problem to the OEM ECU at that time and it's ability to alow for the venting of metered air.

The difficulty lies in that there is no precise way to measure, at least cost effectively for aftermarket companies anyway, the PRECISE amount of air that can "safely" be vented out of the system and not cause a problem for the ECU, in whatever it's current state of tune may be, and it's ability to correctly add fuel to the system in the appropriate ratio. There are innumerable factors to consider that will never be perfectly "tuned" in a single 50/50 valve design to suit all applications.

50/50 valves are essentially trying to "trick" the ECU into believing that enough air is still being recirculated to maintain a proper air/fuel ratio under any given load condition, when, in fact, there is no way to effectively know what ratio should be used, if any at all.

The safe bet is to just use a recirulating valve where recommended and enjoy the security that you know that your ECU is not struggling to maintain a proper air/fuel ratio.

If the added sound is REALLY the most important thing to you, however, you must be willing to accept a level of risk that some problems MAY occur.

While it may be nice to have that blow-off valve (whooshing) sound, I personally feel that it's significantly more important to have a valve that will perform and operate properly for the given application regadless of the amount of noise it makes. I do not feel that valves should be designed to make a particular sound, nor to trick their engine management system, whether factory or aftermarket, into thinking the car is operating properly. Valves are meant to perform a specific function that should be done in a manner best suiting the specific application.

Valve Tuning:

Once you have made your valve choice, regardless of which manufacturer’s valve you select, the same basic tuning principles will apply.

If you are finding that your valve is dumping more air than required, venting too soon, or it is leaking boost before the redline of your application is reached, it is normally an indication that the valve is adjusted or tuned too softly and that a stronger spring or more spring tension is required. Conversely if the valve is failing to dump boost pressure, or you are experiencing valve fluttering at full boost throttle lift, it may be necessary to install a weaker spring or tune the valve to a softer setting.

If you have a valve that uses different springs for tuning and, during the tuning of your valve, you are faced, for example, with a given spring being to strong and another spring being too weak, you can add spacers/shims/washer (which are typically included) to the softer spring to increase the tension by small increments, thus achieving a setting between the two springs.

If your valve uses some sort of adjustment ****, screw, or bolt at the top used to adjust the amount of pre-load on the spring to increase or decrease its tension and, subsequently, its boost holding capacity, unfortunately, there are other things, you must consider first, so read carefully.

First, you must consider what type of spring is used in the valve.

Does it use a cylindrical spring in the shape a can of food, or a conical spring in the shape of a funnel?

A cylindrical spring is the most commonly used type of spring, and while great for most applications, has limited tenability. Cylindrical springs can only be compressed to a certain point to which all of it’s coils are stacked; resting on top of one another. At this point, the spring has reached its full range of travel and can compress no further. In tuning a valve with a cylindrical spring, adding pre-load through an adjustment **** or adding spacer/shims/washers must be done carefully so as not to add to much pre-load that the valve’s piston then has limited travel. Limited travel can result in limited airflow which can inhibit the valve’s ability to perform optimally for the application.

A conical spring offers a much larger range of adjustability than a cylindrical spring within a given valve. A conical spring of the same height as a given cylindrical spring can be compressed much further as each smaller spring coil will rest inside the inner diameter of the next largest coil, preventing a “stacking” effect of the coils. This typically means that more pre-load can be added without limiting piston travel allowing for unobstructed airflow at all pre-load levels.

Also, consider how the spring used in the valve of your choice is manufactured, regardless of which type it is. Cold-winding of springs is a practice used to ensure the strength of the spring and to prevent any relaxing or sagging of any individual coils as the spring is heat cycled through daily usage. This will ensure that the spring retains its rate and boost holding capacity for an extended period of time. Not all manufacturers use cold-winding techniques, so keep that in mind.

With these things in mind, tuning of the valve can commence with caution given to how much pre-load is added, and an understanding that while there may appear to be more adjustment available from the ****, screw, or bolt, the amount of pre-load may already be the maximum allowable amount to not inhibit piston travel, and subsequently airflow volume.

Valve Fluttering:

Valve fluttering is commonly thought to be an automatic indicator of compressor surging, and I would like to put that rumor to rest right now. This could not be further from the truth.

Compressor surging (caused by a bypass valve) implies that the bypass valve is not opening fully to allow the optimal amount of airflow required to keep the compressor wheel of the turbo spinning at an optimal speed.

Bypass valve fluttering will occur under various circumstances, so please consider under what situations you are experiencing fluttering before you presume that compressor surging is taking place, or more importantly, before it is assumed that a problem even exists.

Valve fluttering under wide open throttle or full boost throttle lift, again, typically means that a valve is tuned or adjusted to stiffly, and while this can lead to compressor surging and potential damage over an extended period of time, if the user fixes the issue quickly, no significant damage will occur. It would only be after prolonged use of a valve in an improperly tuned configuration that compressor surging MAY lead to damage or excessive wear on the turbocharger.

Valve fluttering under partial throttle or partial boost throttle lift, on the other hand, is a completely normal occurrence and IS NOT an indication of compressor surging by any measure.

Partial throttle or partial boost valve fluttering is solely an indication that the valve is directly responding to the inconsistent pressure differential on either side of the throttle plate (throttle body).

An internal combustion engine naturally creates a vacuum effect during the intake stroke of a given cylinder. When boost pressure is built from the turbocharger, it will reach a certain level inside the intercooler piping, but as it enters the intake manifold, it is almost instantly reduced by a given amount of vacuum created by the intake stroke of the engine, thus resulting in a marginally lesser amount of boost pressure inside the intake manifold compared to inside the intercooler piping.

Since the bypass valve sees references from both of these pressure sources, the sealing surface of the valve, be it a diaphragm or a piston, will respond to these differences in pressure, as minor or severe as they may be. This sealing surface response is what is creating the fluttering effect at partial throttle or partial boost throttle lift.

It may be more pronounced on some applications than others, and as mentioned above, the OEM Evo valves incorporates a feature to combat this issue, and while it will always be present to a small extent, it is not a problem for the vehicle in any way whatsoever.

--------------------------------------------------------------------------------

Kevin

Mike is off a little bit with his thesis.. When the throttle body slams shut you need the "Valve" in place to release or divert the charge air pressure. If not you basically place a restriction and increase static pressure causing two thing a shock wave back thru the compressor section of the turbocharger, and secondly since the air cannot go anywhere, the compressor wheel bog down in RPM. You can snap the turbine wheel/rotating assy due to the sudden drop in shaft RPM, and the shock hammers out the thrust bearing in the turbocharger.

If a engine that does not have a Bypass or diverter valve once the throttle is opened back up, the turbocharger will take some time to spin back up operating shaft RPM's where present boost was being produced. Basically we are stalling the turbocharger. In some cases you can have a violent shudder and popping noise. The "lag" that Mike mentioned was induced my restricting the air flow on the compressor stage, as a result there will be "LAG" or >> duration of time that the hot side exhaust gases "drive" the turbine wheel producing shaft speed which in turn allows the compressor wheel to build boost..

To answer the original post, the ECU sends a signal to the N75 frequency valve (similar to a fuel injector) the duty cycle will allow manifold pressure to open the actuator that in turn open a mechanical/gate. This gate which on our cars in internal or inside the turbine housing. Once open the exhaust is diverted away from the turbine wheel. Depending on how long of the extent of the swing of the gate/door, the turbine wheel will maintain it's RPM or begin to slow down and lose it's RPM.. As a result, the turbine shaft that is connected the compressor wheel keeps/maintains the boost pressure or it reduces its output from the reduction of RPM.

I have spent many years machining and tweaking the wastegate channel and flow volume thru the gate (K16 or K24's)to improve off throttle/on throttle response. I call it the reduction of lag...

John D II

Kevin,

Mike states that whether you use a recirculating valve or a blow off valve to release the presure - there is no difference in the "turbo lag" as a result of using either method, as the air is beyond the turbos and recirculated to the already charged side of the intake. Do you feel his "lag" analysis to be true or false in regards to the DV valve vs. BOV function and the resulting effect on turbo lag?

calturbo

The lag would then be due to back pressure restricting the air flow.

wross996tt

John, I certainly do not have the depth of knowledge myself...I just have some links to technical information that I have saved over time. My link to answer some basic questions is this one:

Turbo Charging Dynamics



I'm certainly willing to learn more.

Kevin

Folks, we are bleeding off pressure. The turbocharger is still turning at speeds around 150K.. It just doesn't stop when you shift and the throttle-body slam shut. The rotational energy or inertia generates boost.. Guess where the boost goes.. It goes where it's diverted.. If you put it back into the intake track, It's reducing the static pressure/or suction when the turbine wheel starts to get back up to speed.

Venting to atmosphere loses this advantage!!

We are splitting hairs here though.. Once the exhaust starts turning the turbine wheel and we start seeing higher shaft speeds we start to make our boost.. This transition is called LAG.. However, if we can lighten up the load on the compressor side with a "forced induction" from the diverter valve there is less drag placed on the shaft. The turbine wheel will come up to speed quicker..

John D II

Kevin,
Thank you for your explanation.

wross,
Like you, I am trying to learn based on what's out there for information. The reason I am interested in this subject is that I will be installing the Protomotive Y-pipe and intake system shortly - which uses direct vent to the atmosphere. After hearing differing opinions from experienced people in this area, it seems not everyone agrees on this....just like with turbos and everything else. I guess I will form my own opinion based on experience, shortly.

wross996tt

Yeah, John let us know....good luck with the upgrades!