[wrxtc]

I think I understand how and why the wastegate affects turbo performance but I am not 100% sure.

It seems very simple to me. If one wastegate setup results in better performance than another (as some people are showing with for example: FP Green turbos with internal gates vs those with external gates) it is because one wastegate setup is better able to stay closed (or closer to the fully closed position) to allow more of the exhaust gas to operate on the turbine wheel.

So I guess that there's only so far you can go with the amount of exhaust flow that an internal gate can hold back due to the enormous force of the exhaust entering the turbo overcoming whatever spring strength you may have on it and/or overcoming the strength of the actuator/solenoid controlling the wastegate.

Are internal wastegates less able to stay closed because the extra pressurization of the exhaust gas being expelled from the turbine (i.e not the waste gas, the gas flowing out to the exhaust system after flowing through the turbine) into the exhaust housing making it more difficult?

Is this also why we sometimes experience 'wastegate flutter' with the stock turbo? Is the stock internal wastegate just too weak to stay shut during certain partial throttle situations due to the coarse resolution of the stock boost control or because it just needs a stiffer spring or better boost control solenoid?

I doubt an external gate would be of much benefit to the stock turbo because it does not have a lot of headroom for efficient flow of much more air than it moves in stock form. But I can see how an external gate is almost mandatory for a large turbo unless it has an absolutely massive exhaust housing with a monster wastegate flapper with a super strong spring and very good control mechanism.

Will someone let me know if I have some misconceptions here? This turbo stuff is very interesting to me. I've been reading forums like this since I got my 04 STi and slowly it's all been oozing into my brain. I'm just not sure how much of it was posted by people who only -think- they know what they are talking about, lol.

I have some books on order that should clear ALL this stuff up but they won't get here for weeks!

[rob142sti]

"Is this also why we sometimes experience 'wastegate flutter' with the stock turbo? Is the stock internal wastegate just too weak to stay shut during certain partial throttle situations due to the coarse resolution of the stock boost control or because it just needs a stiffer spring or better boost control solenoid?"

wastegate flutter is annoying as hell.. how do you get rid of it?

[wrxtc]

Originally Posted by rob142sti

wastegate flutter is annoying as hell.. how do you get rid of it?

That's one of the things I'd like to learn. I'm hoping one of the experts will grace us with their knowledge.

[RiX]

With a decent EBC (e.g. GReddy e-01), you can set a target boost start value such that the EBC will keep the wastegate shut until a target boost is reached (e.g. 11-12psi). I wonder if this is what you are looking for?

[wrxtc]

Originally Posted by rjhang

With a decent EBC (e.g. GReddy e-01), you can set a target boost start value such that the EBC will keep the wastegate shut until a target boost is reached (e.g. 11-12psi). I wonder if this is what you are looking for?

Well not exactly. I mean the stock ECU can change target boost values with reflashing like EcuTek and Cobb AccessPort. As I understand it an EBC (electronic boost controller) is mainly useful when you want/need to alter boost levels outside of what the stock ECU wants and/or use a turbo that the stock boost control simply can't handle.

I'm interested in learning better how turbocharger wastegates work and what causes them not to work well enough in some cases.

Another thing is that I do not really understand what causes wastegate flutter at all. My guess is that it happens because your throttle level is right at the transition point between opening and closing the wastegate and the turbulence of the exhaust entering the housing is causing it to wiggle because it's just not sure which position it wants because the force the controller is putting on it is kind of weak.

[donmei]

hoo boy. I can shed some light, but this post will be long. Best to start at the beginning.

Back in the old days before electronics, wastegates were mechanically controlled. Think of the old 911 turbo, Buick regal turbo (pre GN) and Saab 99 turbo.

The intake manifold had a hose coming off of it. The hose went to a thing commonly called a
1) vacume solenoid
2) wastegate solenoid
3) wastegate controller

They're all the same thing. Its the goldish colored cylinder on the turbo. It is essentially a metal can with a hose on one end and a diaphragm in the middle. As the hose blows or sucks against the sealed volume of the can, the diaphragm moves in or out. The diaphragm is connected to an arm that translates its motion into useful work. Finally, there is a spring that is supposed to keep the diaphragm and the arm pushed in one direction until the pressure reaches a point where the whole assemply moves.

So, in the old cars the boost would reach a certain level and the pressure would push the diaphragm, connected to the arm coming out of the solenoid, connected by a rod, connected to the wastegate on the exhaust side. The wastegate would open and dump as much exhaust AROUND the exhaust turbine as was necessary to prevent boost from rising.

Ok, time for a brief aside. This is when manual boost controllers really worked great. by using a $6 valve from a plumbing supply shop, it was possible to bleed some of this air off. This would cause the solenoid to feel less than the total amount of pressure so it would actuate later, allowing for more boost. I used this system in my Saab 99 turbo (along with a boost gauge and water injection) to significantly bump the power of the car. (still not very impressive. Stock was 135 hp, I'd guess I got 160 hp)

Enter the age of electronics.

That hose connected to the wastegate solenoid is no longer connected directly to the pressurized side of the intake system.

Now a days, the computer senses that boost has reached a certain level. Then it uses some of that boost to pressurize the solenoid to open the wastegate. Botom line is that the solenoid doesn't see any pressure unless the ECU wants it to.

This is why manual boost controlers (mbc) don't work so well anymore. Lets say the ecu says it wants to start tapering boost off to 12psi. But you've introduced a mbc, essentially a LEAK in the system. The ecu trys to open the wastegate but you are bleeding off the air the ECU is using to try to open the wastegate. The ecu sees that it is requesting 12psi but is getting 15 psi (because of the mbc). Here I'm not 100% sure of how Subaru deals with it, but the Bosch system on VWs will begin to pull ignition timing as a defensive mechanism against what it senses as run-away boost. This HURTS power.

So back to how things are now: an electronic system using pneumatics to control the wastegate. This is a stupid way to controll a wastegate. Since the system and feedback loop are now electronic not pneumatic, an electronic solenoid should be superior. But no one uses them because they all want to use standard systems. (all the bosch and Nipondenso systems (which makes up the ignition and injection systems of just about every car not made in the USA) are designed to work with standard vacume solenoids for wastegate controllers)

I think someone has an electronic wastegate solenoid now, but its aftermarket. (Perrin?)

So, what does the ideal wastegate do. Well first, it stays COMPLETELY closed until boost reaches predetermined levels. Then it opens as is required to maintain that boost. It also flows well enough so that the boost does not rise above predetermined levels.

So, how can an external wastegate perform better. Well, it can leak less, allowing boost to build more quickly. But most importantly, it can be more responsive to changes in throttle and can flow much better than an internal wastegate, so with a big turbo boost doesn't creep (there's that word again) higher than you want it to.

I hope this helps.

Don

p.s. What does the future bring?? Hopefully lots. With electonic wastegate control, we can begin to use the wastegate as a kind of secondary throttle. Lets look at a typical partial throttle , acceleration scenario. Your car is accelerating, you are boosting, but it is not a full throttle blast. This is a far more typical situation than a full throttle/redline run. What yo have here is a closed wastegate and a turbo trying to make as much boost as is physically possible. This intake air then runs up and SLAMS directly into a nearly closed throttle plate. Net result is that the turbo is working harder than it has to. The engine is hotter than it has to be. The intake air is hotter than it has to be. Now lets pretend that the system is electronically controlled. You want a bit of acceleration, but nothing antisocial. The ecu (along with throttle by wire) instead leaves the wastegate fully OPEN, and fairly rapidly opens the throttle. So now you are requesting lets say 150 hp. The car is making it without turbo charging. Now you tip your foot in a bit more, 220 hp. More than the car can make without turbocharging. The throttle is still wide open, but the ECU now starts to close the wastegate, bringing boost up. So now you have a car with a wide open throttle, and a partially open wastegate. Much more efficient than a partially open throttle with a turbo behind it boosting all it can.

Hope this helps.

[wrxtc]

Dude!! Thanks for the post donmei!! This has been truly enlightening. I have some tuning books coming in the mail in a while. I am going to study them hard and hopefully get the Cobb street tuner and the Perrin electronic boost control solenoid!

From what you're saying the electronic solenoid should allow far better gas economy during part throttle as well as possibly eliminating wastegate flutter AND better throttle response all at the same time! The only downside is that I need a tuner who knows what he's doing. If I don't feel I learned enough after reading these books I have on order I'll have to take a drive down to Atlanta as that's the closest place to where I live that has tuners that know Subarus (or even tuning turbocharged motors for that matter).

[chowder31]

so would putting the perrin boost controller on say a stock car, have any performance gains ie: better mpg, better throttle response, more accurate boost?

[rob142sti]

i know this is off of the topic but looking at the srt-4 wastegate its so much bigger( the gold cylinder on the outside of turbo) so is there any aftermarket better wastegates for us to allow more boost?

[donmei]

wrxtc- no the electronic controller won't do those things you said. What I said is that with electronic solenoids, engine manufacturers could start using the wastegate as a sort of throttle. But no one is doing that yet. In theory, the perin shoudl give you better control of boost though.

Rob - that gold thing is not the wastegate. It is the wastegate solenoid (aka wastegate controler) It is what the ecu uses to actuate the wastegate. And size doesn't matter. (at least there.)

Don