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4 port boost controller

Boost Control

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Discussion and questions related to the course Boost Control

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What is the purpose, benefit/downside to four port boost controllers. How are they piped on externally waste gated setups


but i have been told they are a lot more sensitive to duty cycle changes than a 3 port.

can anyone confirm this and are there any circumstances that contribute to the sensitivity? High boost low boost etc.

With a 4 port solenoid you can completely remove pressure from the bottom port of the wastegate (with a typical 3 port installation this side of the wastegate always has boost pressure applied to it). This provides the potential for a much wider range of boost control than a 3 port solenoid can achieve since with the 3 port we always have exhaust pressure acting against the wastegate valve and trying to open it, as well as the boost in the bottom of the wastegate head also trying to open it.

To give some example, with a 10 psi spring in a wastegate, you may be able to achieve a maximum boost pressure of perhaps 25 psi with a 3 port (hence a range of 15 psi) but a 4 port may allow you to reach 35 psi or thereabouts.

can this be applied in principle to a blow off valve on the intake tube before entering the throttle body and supercharger to control over boost and what air valve bodies are most utilized for this application

You could make it work but if you're really concerned about overboost on a supercharger, size the system correctly so it doesn't tend to overboost in the first place, and put a fuel cut in for emergencies.


do you recommend this setup/where have you used it before? Jay's tech tips on realstreet youtube channel makes it sound like the way to go. Plumbing wise the what are the 4 ports, 1 normally closed (to the top of the WG as in exhausting normally) 2 normally closed (to the bottom of the waste gate holding it closed against engine exhaust pressure) 3 input 4 vent? is duty cycle set up the same on a 4 port as a 3 port? IE will the parameters be the same, starting with open loop and then adding in your PID for closed loop? For background I'm new to tuning and using a AEM infinity on a dual externally waste gated twin turbo system.


It really depends what range of boost control you need. Certainly the 4 port will give you a wider range of control than a 3 port solenoid can. Realistically the only downside I see with a 4 port over a 3 port is that the boost will be a little more sensitive to changes in duty cycle.

I was just about the create a new topic on 4 port boost control solenoids when I saw this post.

Andre, why wasn't the 4 port boost control solenoid described and dealt with in the boost control course?

@Chris, we may add a module on these solenoids. In my own experience they still aren't that common outside of drag racing, however I'll admit they do seem to be gaining popularity. The reality though is that other than the plumbing side of things, the operation and tuning is identical.

Thanks a lot for the response and understood.


Awesome information.

Hope, you don't mind me bringing an old topic back, but I didn't want to create one more 4 port topic, as there are quite a few already.

So, I am running a TurboSmart IWG-75 currently on my STi and getting to a point where I am about to turn up the WGDC (right now it is all 0), but as I recently started to look at log files, something seems to be weird and want to make sure I am not missing anything.

In the attached pictures you can see the plumbing and a screenshot of a recent log I did during a short WOT pull.

The thing that I can't get my head around is how come my MAP reach about 1.3 Bar boost when the springs in the wastegate actuator is 14psi rated and the boost pressure is applied to the top of the diaphragm which in turn should reduce the boost even further in my mind as the other port is exposed to the intake pipe with WGDC=0.

I am thinking about doing an other run with the wg actuator totally disconnected to see if the boost is going to increase even further in that case, but before I do that, I thought to give it a try here and see what you guys think.

Couple of side notes: I know the EBCS plumbing is reversed, but I tested with an air compressor and the valve inside is not going to be shut from this direction, so that must not effect anything. The turbo I run is a Litchfields LM450, but I don't think it matters from this perspective.

Thanks a lot for any insights.


Attached Files


The pressure rating of the wastegate springs takes into account the pressure being applied to them on the other side of the diaphragm. So with boost pressure applied to the top port of the wastegate, ignoring a lot of variables, the boost should be about 14psi.

If you pull all the lines off the actuator, you are relying on exhaust back pressure in the turbine housing acting on the internal wastegate flap to overcome the spring pressure of the wastegate actuator. This will dramatically increase boost as the wastegate flap is quite a small area (less than a square inch). The boost will increase quite dramatically.

Sometimes the pressure source location for your boost control can cause an issue. If it is taken from the intake manifold instead of the compressor housing for instance, it often sees a lower pressure, as you usually have a pressure drop across the intercooler.

In my personal experience, most smaller frame stock and high flow turbos have insufficient internal wastegate flapper area for adequate control, and very low priority flow, with the port entering at 90 degrees to the exhaust flow, with the area recessed. SO it isn't uncommon to have boost higher than spring pressure, due to poor flow, without a modified turbine housing. Often a light teardrop transition into the flapper area is all thats needed, and sometimes there is room to open the port up a little bit too.

If you want to find the minimum possible boost with the current spring configuration, connect the hose labelled "IN" from your diagram directly to the swivel barb on the front of the IWG-75, make sure the port on the other side of the diaphram is open to atmosphere, and complete another pull, otherwise keep your plumbing, and unplug the solenoid, just in case you have missed a setting, and you are infact applying a little bit of duty to the valve, and recheck what boost you achieve.

Thanks Nathan.

Appreciate your inputs. I'll do an other pull as you mentioned then I'll remove one of the springs and see how that works out.

I might be missing it... or maybe it doesn't matter; but isn't the A port your out? Whereas the A port should go to the top of the wastegate. Similarly the B port is your IN port which should go to the bottom of the waste gate. Then the IN port on the solenoid would be the pressure source from your turbo and the EXH port would vent to atmosphere or your intake.

I'm basing this off of the following Turbosmart instructions: https://www.turbosmart.com/wp-content/uploads/instructions/Boost_Controller_Electronic_Electric_Solenoid_4_Port_Fitting_Instructions_Installation/051413053034.html

BTW - I am wrestling with my own boost issues and configuring my M150, so I may be off base here and far from an expert.

I don't think it matters with the 4-port, since it reverses the inlet/outlet on each part of the cycle. So whether you sit as 55% duty cycle or 45% duty cycle doens't really matter. You use the "invert output" to make the software config match the physical plumbing.


You are absolutely right. I mentioned that in my post as well, and I actually wasn't sure if that could cause a problem. What I was thinking about is closing the valve from the reversed direction of air flow, but I tested the airflow with an airgun (6bar pressure) and it did not do anything, so I left it like that.


Why do you think this would effect the duty cycle? I don't really see that, although I don't even think it matter much as I am dialing in the WGDC from scratch anyhow.



I think of the duty cycle as the percentage of time spent on one plumbing connection. The inverse of the duty cycle (ie, 100 - Duty Cycle) is the percentage of time spent on the opposite plumbing connection. So if you invert the plumbing, you can just invert the duty cycle to achieve the same result.

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