Bad Wastegate?
03-12-08, 11:01 PM
#1
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Bad Wastegate?
I need help in figuring out this setup and what the previous owner was thinking here. First of all, relevant mods are Single T60 Turbo and HKS Ext WG and HKS Boost Controller. Second, Ever since I bought the car, the WG only had one vacuum line hooked up, going from the compressor housing to the side-port of WG. I think I found the boost controller solenoid valve and I think the lines that would goto to the WG are just looped back into itself. Now with this setup I would get consistent boost patterns. 12lbs until it hit the last 1000 rpms or so and it shot up to 15lbs.
I had concerns that the missing vacuum line might be contributing to a rough idle so I took the line going to the side port and tee'd it off so that I could run that same line to both the top and side ports. I figured with no restriction on the vacuum line coming from the top-port, the boost would stay the same or drop.
I took it for test drive, and I couldn't even bring it to redline. Boost pressure shot up like crazy. In record time I hit 15lbs at like 4500 rpm and I shut her down. It scared the crap out of me in the "Holy **** I'm gonna pop my engine like a cheap baloon" type of crap. I'm sure I would've been deep into the 20's had I redlined it. WTF???
1. Is this normal? I thought a disconnected vacuum line to the WG would result in overboosting issues?
2. What was the previous owner thinking in looping back the BC valve lines? Why set up a boost controller so the lines doing the controlling are disconnected?
3. Would there be any side effects from leaving the top-port on the WG disconnected like that? Vacuum leak? F.O.D.?
I had concerns that the missing vacuum line might be contributing to a rough idle so I took the line going to the side port and tee'd it off so that I could run that same line to both the top and side ports. I figured with no restriction on the vacuum line coming from the top-port, the boost would stay the same or drop.
I took it for test drive, and I couldn't even bring it to redline. Boost pressure shot up like crazy. In record time I hit 15lbs at like 4500 rpm and I shut her down. It scared the crap out of me in the "Holy **** I'm gonna pop my engine like a cheap baloon" type of crap. I'm sure I would've been deep into the 20's had I redlined it. WTF???
1. Is this normal? I thought a disconnected vacuum line to the WG would result in overboosting issues?
2. What was the previous owner thinking in looping back the BC valve lines? Why set up a boost controller so the lines doing the controlling are disconnected?
3. Would there be any side effects from leaving the top-port on the WG disconnected like that? Vacuum leak? F.O.D.?
03-12-08, 11:48 PM
#2
If you where only running spring pressure on the wastegate and not using the boost controller you would only run the side port and leave the top port open.
If you where running the boost controller hooked up then you would run it like this.
You have to figure out your NC and COM ports.
I've heard of people running there boost controllers on the external wastegates like internal ones with the top port open and the solenoid spliced into the side port with some success.
I run mine like the picture above and have not seen any issues with it. This is with a Greddy Profec B spec 2.
If your seeing higher boost pressures as your RPM's increase then your wastegate itself might not be big enough or something else might be wrong with it.
If someone sees anything wrong with what I said then please correct me.
I hate giving out wrong info.
If you where running the boost controller hooked up then you would run it like this.
You have to figure out your NC and COM ports.
I've heard of people running there boost controllers on the external wastegates like internal ones with the top port open and the solenoid spliced into the side port with some success.
I run mine like the picture above and have not seen any issues with it. This is with a Greddy Profec B spec 2.
If your seeing higher boost pressures as your RPM's increase then your wastegate itself might not be big enough or something else might be wrong with it.
If someone sees anything wrong with what I said then please correct me.
I hate giving out wrong info.
03-13-08, 07:26 AM
#3
Previous reply looks pretty comple IMO.
A disconnected signal line yes. Which would be the single vaccum line from the compressor housing to the wastegate's side port.
He may have had trouble with the unit or couldn't get it hooked up right so he simply returned the wastegate to a configuration to run on spring pressure alone. He was thinking smart.
None at all. I ran like this for a LONG time with a manual boost controller, and anyone with a single turbo who is running on spring pressure will be running like this. Absolutely nothing wrong with the original setup at all.
None at all. I ran like this for a LONG time with a manual boost controller, and anyone with a single turbo who is running on spring pressure will be running like this. Absolutely nothing wrong with the original setup at all.
03-13-08, 11:50 AM
#4
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Gotcha, I guess I'll go ahead hook it back up the way it was before.
I have one more related question tho. In my neverending quest for a solid idle, I heard that an Ext WG dump not routed back to the cat-back, just dumping to the atmosphere, would contribute to a rough idle. Is that true?
I have one more related question tho. In my neverending quest for a solid idle, I heard that an Ext WG dump not routed back to the cat-back, just dumping to the atmosphere, would contribute to a rough idle. Is that true?
03-13-08, 11:57 AM
#5
No.
Its possible that comment is stemming from someone who has had an external gate with a minor leak which gave an exhaust leak sound to the idle, but no, if the wastegate's workign properly there is no reason for the car to not idle regularly with a wastegate dumped to atmosphere.
Its possible that comment is stemming from someone who has had an external gate with a minor leak which gave an exhaust leak sound to the idle, but no, if the wastegate's workign properly there is no reason for the car to not idle regularly with a wastegate dumped to atmosphere.
03-13-08, 01:41 PM
#6
Look, if you run a pressure source from the compressor housing to the side port of the wastegate (with no boost controller and top wastegate port vented), that's it. Your boost can't go any lower. You need a different manifold/wastegate combination.
Now, if you are running an EBC you may want to get the pressure source from something after the intercooler. Why? the more pressure the top port sees, the higher the boost--but only in an EBC configuration like in the pic posted above.
To summarize, to get the lowest boost possible on an external wastegate you want high pressure going to the side port on the wastegate and no pressure going to the top.
https://www.rx7club.com/showthread.p...ighlight=AVC-R
Hooking an EBC into the side port of an external wastegate (similar to an MBC setup) will get the job done, but you lose the advantage of having the EBC control how much pressure is pushing the spring closed (in the top port config), possibly hurting your torque curve.
Now, if you are running an EBC you may want to get the pressure source from something after the intercooler. Why? the more pressure the top port sees, the higher the boost--but only in an EBC configuration like in the pic posted above.
To summarize, to get the lowest boost possible on an external wastegate you want high pressure going to the side port on the wastegate and no pressure going to the top.
Internal wastegate: Internal wastegate is controlled by a actuator with a rod. Inside the actuator, there is a spring and on top of it, there is diaphragm. On the outside, there is nipple to connect to the boost source. If the spring is set for 10 psi, that means at 10 psi, there is going to be enough force to push the diaphragm down and then extend the rod to open the internal wastegate. When it's connected to a boost controller, the solenoid valve's function is to delay the boost signal or reduce the signal. Let's say you set the boost controller to 15 psi. That means at 15 psi, the duty cycle of the solenoid will simulate 10 psi. So 15 psi is going into the solenoid valve but 10 psi coming out and goes into the actuator. When the duty cycle is at 100%, it's like the solenoid valve is totally open so you will get 10 psi like you never have a boost controller. If the duty cycle is 0%, that means the solenoid valve is totally closed and the actuator rod will never move and the internal wastegate will never open. So higher the duty cycle, lower the boost.
External wastegate: Inisde there is a spring, diaphragm, and a valve. The diaphragm separates two chambers inside the wastegate. The bottom port of the wastegate feeds the bottom chamber and the top port of the wastegate feeds the top chamber. When you don't use a boost controller, you connect a boost source to the bottom port. Let's say if the spring is a 10 psi spring, at 10 psi, there is going to be enough force to push the diaphragm up and move the valve up to vent out the exhaust. When you connect to a boost controller to the external wastegate, You connect another boost source to the top port and with the solenoid valve inline. Whatever boost you feed to the top port will be added to the boost that's set by the spring. Let's say if the spring is 10 psi and you have 5 psi going into the top port, your overall boost will be 15 psi. So if the solenoid valve is at 100%, that will give you unlimited boost because the wastegate is not going to open. There is going to be equal pressure from the top and bottom chambers and the diaphragm will not move, hence the wastegate valve will not move to vent the exhaust. So if the duty cycle is at 0%, that means the valve is totally closed that there is not going to be any pressure going into the top port. You wastegate will be opening at 10 psi as if there is no boost controller. So the higher the duty cycle, the higher the boost.
This is why you have to set the boost controller for external or internal.
External wastegate: Inisde there is a spring, diaphragm, and a valve. The diaphragm separates two chambers inside the wastegate. The bottom port of the wastegate feeds the bottom chamber and the top port of the wastegate feeds the top chamber. When you don't use a boost controller, you connect a boost source to the bottom port. Let's say if the spring is a 10 psi spring, at 10 psi, there is going to be enough force to push the diaphragm up and move the valve up to vent out the exhaust. When you connect to a boost controller to the external wastegate, You connect another boost source to the top port and with the solenoid valve inline. Whatever boost you feed to the top port will be added to the boost that's set by the spring. Let's say if the spring is 10 psi and you have 5 psi going into the top port, your overall boost will be 15 psi. So if the solenoid valve is at 100%, that will give you unlimited boost because the wastegate is not going to open. There is going to be equal pressure from the top and bottom chambers and the diaphragm will not move, hence the wastegate valve will not move to vent the exhaust. So if the duty cycle is at 0%, that means the valve is totally closed that there is not going to be any pressure going into the top port. You wastegate will be opening at 10 psi as if there is no boost controller. So the higher the duty cycle, the higher the boost.
This is why you have to set the boost controller for external or internal.
Hooking an EBC into the side port of an external wastegate (similar to an MBC setup) will get the job done, but you lose the advantage of having the EBC control how much pressure is pushing the spring closed (in the top port config), possibly hurting your torque curve.
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