External Wastegate

[fliprayzin240sx]

K I'm having issues with my external wastegate. Figured, best way for me to figure out what it could be is by first understanding how this thing works. I have an older Trust/Greddy External wastegate.



Has 2 nipples on it, I know the side is the vacuum port and the top is the line for the controller.



I just dont understand how a boost controller regulates the boost via the top port. Doesnt boost controllers control boost by restricting the amount of air going thru it?

So lets say you have your boost controller to 18 psi but you have a 14 psi spring. Once you hit 14 psi, the boost controller shouldnt be letting air thru till 18 psi. So if there's no pressure on the line after the boost controller and the spring is already seeing 14 psi, how is it keeping the spring from opening?

My issue is that I was boosting 1.2-1.4 bar with the boost controller off. Some times it would overboost to 1.6. I was told to open the wastegate up and make sure nothing is binding. I opened it and cleaned it up. Slapped it all back together, didnt touch the adjustment screw up top and now I'm only hitting .7.

[XnTroubleX]

IIRC, the amount of boost is first sent to the boost controller. after it reaches your desired amount of psi it releases and sends to the wastegate,since your desired amount of boost is more than the spring in the wastegate, it pushes the spring and allows excess pressure to bypass,, I hope I wrote that in a way you can understand!

[fliprayzin240sx]

Originally Posted by XnTroubleX

IIRC, the amount of boost is first sent to the boost controller. after it reaches your desired amount of psi it releases and sends to the wastegate,since your desired amount of boost is more than the spring in the wastegate, it pushes the spring and allows excess pressure to bypass,, I hope I wrote that in a way you can understand!

See thats the part that gets me, you said the boost controller will release the pressure thru it once it reaches the desired amount. But since that amount is higher than what the spring is rated for, so the spring will let the wastegate open up before the boost controller opens up.

[XnTroubleX]

No it shouldnt, your spring shouldnt open up till your boost controller opens because your boost controller is the first in line to recieve the pressure.

[mysharonna]

I think you can almost double the spring pressure in psi. So if you have a 7 psi spring then you can do 14 psi with a boost controller.

I would think that it would be best to run a spring that is close to the psi you would like to run at all times so there is now as much work going on in the boost controller.

[XnTroubleX]

Originally Posted by mysharonna

I think you can almost double the spring pressure in psi. So if you have a 7 psi spring then you can do 14 psi with a boost controller.

I would think that it would be best to run a spring that is close to the psi you would like to run at all times so there is now as much work going on in the boost controller.

Agreed!!

[codyace]

The top port will goto the selenoid.

The other side of the selenoid will goto a vacuum source

THe middle part on the gate will goto any vacuum source

I don't like mixing/splicing into source lines as they sometimes don't like to work with each other.

So lets say you have your boost controller to 18 psi but you have a 14 psi spring. Once you hit 14 psi, the boost controller shouldnt be letting air thru till 18 psi. So if there's no pressure on the line after the boost controller and the spring is already seeing 14 psi, how is it keeping the spring from opening?

The top port is normally left open with an MBC, allow it to work through 'full time' true atmospheric pressure. Remember, air wants to regulate itself, so if their is an area of high pressure (boost) and then it's introduced to an area of lower pressure (air), air will rush out to the 'open', thus causing the valve to open.

With an electronic, it regulates the 'true atmospheric' part of the equation and regulates this. Most celenoids have 3 sources...top of gate, vacuum source, and a third (either open port or hidden) one for atmospheric pressure. (Lets also not forget the brains source which regulates thes tepper motor).

So the celenoid is closed. 7 psi in the gate won't open because that top port is 'shut off'. The ebc brain senses the desired boost you determined, and the electronically compares that to the celenoids vacuum source, and together then it opens that third 'port' (atmosphere) to make the gate 'open' (tricking it's 7 psi spring at opening at 14 psi.


Hope that makes sense.

[anotherblusi]

Its spelled solenoid buddy...

And heres an easier explanation.

This is for the ideal situation. So the top portion that you took apart exposes the diaphragm. Without any spring inside, if you supply pressure to the lower port, the valve will open and if you supply pressure to the top port it will close the valve. Now with say a 7psi spring on top of the diaphragm. The lower port will now need to see a pressure of 7+psi in order for the valve to open. This is what allows you to hold 7psi of boost and not go over.

Now with a boost controller on the top port, it can supply added pressure to the spring pressure, essentially increasing the amount of boost required to open the wastegate.

Also with the HKS wastegate it also has an adjustment screw on top that can compress/decompress the spring. Then by compressing the spring you can increase the spring pressure and thus increase the amount of boost required to open the wastegate. You can test this by supplying incremental amounts of pressure to the side and see when the valve opens.

But in reality you also have exhaust gasses supplying pressure/vacuum to the bottom of the valve. This will be significantly dependant on your manifold design. This basically means that even though you have a 7psi spring in the wastegate, you will not necessarily see 7psi of boost. It can be less or in most cases you will see more boost.

Finally, the exhaust gas pressure/vacuum in the manifold is very dynamic, changing at different rpms, loads, etc.... This is what usually causes boost creep and spikes. Basically what it boils down to is that you just have to try a few different spring pressures that gets you the boost you want.

[codyace]

Originally Posted by anotherblusi

Its spelled solenoid buddy...

And heres an easier explanation.

This is for the ideal situation. So the top portion that you took apart exposes the diaphragm. Without any spring inside, if you supply pressure to the lower port, the valve will open and if you supply pressure to the top port it will close the valve. Now with say a 7psi spring on top of the diaphragm. The lower port will now need to see a pressure of 7+psi in order for the valve to open. This is what allows you to hold 7psi of boost and not go over.

Now with a boost controller on the top port, it can supply added pressure to the spring pressure, essentially increasing the amount of boost required to open the wastegate.

Also with the HKS wastegate it also has an adjustment screw on top that can compress/decompress the spring. Then by compressing the spring you can increase the spring pressure and thus increase the amount of boost required to open the wastegate. You can test this by supplying incremental amounts of pressure to the side and see when the valve opens.

But in reality you also have exhaust gasses supplying pressure/vacuum to the bottom of the valve. This will be significantly dependant on your manifold design. This basically means that even though you have a 7psi spring in the wastegate, you will not necessarily see 7psi of boost. It can be less or in most cases you will see more boost.

Finally, the exhaust gas pressure/vacuum in the manifold is very dynamic, changing at different rpms, loads, etc.... This is what usually causes boost creep and spikes. Basically what it boils down to is that you just have to try a few different spring pressures that gets you the boost you want.

Thanks for the spelling advice. Now if only you could work on your technical advice you'd be a ZILVIA MASTER. The EBC works exactly as I described in relation to his EWG. Sure I don't have the 'Mr Science' terminology you may have been looking for, but at least the description is correct.

Certainly every EWG is a bit different, but the function is the same in relation to EBC (this side of a Synapse, but that's a bit goofy anyway)

[fliprayzin240sx]

K so if I have a tear in the diaphram...would that cause it to open up sooner? Like I said, it was boosting at 1.2-1.4 ish with just the vacuum reference port connected. I tore it apart to see whats going on with it because it was spiking to 1.6 once in a while. Put everything back together and now I'm only hitting .7. Would a tear cause this? Also, I have no clue what the spring is rated for so I'm just putting up info as far as how it was working prior.