wastegate operation

[smoothest_vibe]

Hi. I am installing a t3/t4 turbo and 46mm external wastegate on a 98 eclipse gst. The problem that i have is that when the boost hits about 15 or 16 psi the wastegate opens, but then boost drops to about 11 psi. it keeps surging like that about every half second. One thing is that i had to install the w/g backwards from the diagram to make it fit. Could that be the problem? And i don't have any boost controller on it, i have a line running strtaight from the turbo to the w/g so it just opens at the preset pressure of the w/g. any idea's how i can get the boost at a steady 15 psi?

 

[GVR4592]

What did you install backwards? It kind of sounds like compressor surge, what turbo do you have?

 

[patty AT forge]

What kind of wastegate? Probably a 2 bolt Tial/Turbonetics style...
What is the wastegate spring rated at?
No idea what your setup looks like but you will probably need to take a hammer to whatever is preventing you from installing the WG correctly or make an extension for the wastegate port to move it to where it will fit.

 

[smoothest_vibe]

it's an xspower wastegate and turbo

You must be logged in to view this image or video.

The website says the spring is set at 7.8 psi but that doesn't agree with my boost gauge. I have tested the gauge and it seems to be accurate.
The reason it won't fit the direction that they say is because the power steering pump is in the way. Right now the exhaust is flowing in the outlet and out the inlet. I am wondering if the exhaust pressure is holding thr valve shut a bit longer than it should.

 

[kenamond]

it's an xspower wastegate and turbo

You must be logged in to view this image or video.

The website says the spring is set at 7.8 psi but that doesn't agree with my boost gauge. I have tested the gauge and it seems to be accurate.
The reason it won't fit the direction that they say is because the power steering pump is in the way. Right now the exhaust is flowing in the outlet and out the inlet. I am wondering if the exhaust pressure is holding thr valve shut a bit longer than it should.

I wouldn't be suprised if the reversal of the WG is your problem. If the valve is being held shut by manifold pressure rather than the spring, then you'd need a much higher force on the spring to open it (maybe that's why you hit 16psi), then when it's open, your boost drops down, and the force holding the wastegate open drops down, and the mani pressure slams the valve shut again, and you repeat that cycle. It all depends on the WG design, and I don't know anything about your WG model, but that could certainly be the problem. In an internal gate, the WG holds it closed, and when the WG is actuated, the exhaust gasses will help push it open. If you reverse this, the WG has to pull it open against the exhaust pressure. It's like trying to open the door to a car submerged in water with air in the cabin verses opening the door of a car full of water with air outside; you (the WG) have to push much harder to overcome the water pressure in the first case, but the water pressure will help you pull it open in the second case.

 

[smoothest_vibe]

That sounds logical to me. I think i'll try and make an extension for it and mount it somewhere else. Thanks for the help.