I was just wondering what the wastegate is for. To my understanding, the wastegate prevents the turbo from building up too much boost by venting off the pressure in excess of the desired peak boost. Is that right? And if so, then why do i hear my wastegate flutter when i'm nowhere near peak boost? If some you tech gods out there could help me out, i'd appreciate it. Just trying to understand my car better.

 

yes, the wg bypasses the exhaust turbine, essentially removing the "drive" power from the turbo. it does NOT directly work on the intake air.

the flutter occurs when the wastegate is partially opened, and pulses of exhaust gasses push it open a little more.

hth
ken

 

What tell it when to open?

 

the ecu tells it when to open. if you look at the turbo, you'll see a "T" in the boost control hoses. one side of the T goes to the compressor outlet, another goes to the wastegate actuator, the third goes to a solenoid. The ecu opens and closes the solenoid to control boost pressure. when the solenoid is open, pressure is vented back to the intake preventing the wastegate from opening. when the solenoid closes, the wastegate opens.

 

So how come the ecu tells the wastegate to open so early? I mean, why does the ecu want to bypass the turbine before i reach peak boost?

 

To prevent overboost.

Because it takes some time for the excess exhaust gases to be bleed off. So, in order for your car to run, lets say 10psi, the wastegate needs to start opening prior to 10psi. Otherwise it will overshoot.

 

I mean, for example i'll be cruisin at about 2500 rpm, and then speed up some, and at around 3000 to 3200 rpm, i'll hear the wastegate flutter. I'll look at my boost gauge, and i'll be barely above .02 mPa which is only like 3 psi. So i'm nowhere near peak boost.

 

The ECU isn't always telling the wastegate to open early. That depends more on the spring rate of the WG. If the spring rate is 8 pounds, the gasses will start to push it open before the ECU controls it to open. This will result in no spike, but boost will also build slower. I bet if you had a WG with a 12 pound spring, our cars would be able to build more boost in 1st and 2nd more easily and quicker.

 

Thats your blow off vavle.

 

You are wrong. The ECU does tell the wastegate to open sooner. That is why stock, WRX's run 14psi peak and more like 7 psi at the redline. Then if you put a EBC, you can run X psi all the way to the redline.

 

It tells it to open early for protection. Subaru is very very good at under tuning its cars. That's why the is so much the aftermarket can do with them. Subaru does not want any damage to becaused by over boost this can hurt the turbo and the engine. There are things that you can do to vary the wastegate performance.


1. Ecu reflash or piggy back. This will vary the amout of boost that the turbo will build by controlling the stock boost selonoid. This seems to be a good way to go because you are working within all the Subaru ecu standards.

2. You can get an MBC (manual boost controller) this is also a way to change the wastegate operation. The problem is that you are fooling the ecu and the wategate. This is very cheap but you may notice that boost will be at peak during half throttle. This is great for speed but may be harmful for your turbo, engine and fuel budget.

These are just two things that I know about. There are more ways like an ebc(electronic boost controller). I am not sure how this works but i believe that it is like an MBC but it controls the wastegate selonoid. this may be for more xperienced tuners. I am pretty new to tuning but doing some research this is what i've learned.

 

I thought the blowoff valve vents when i let off the gas, not when i give it more throttle.

 

At 2500 to 3000 rpm the amount of exhaust you have flowing out of the engine is enough to generate full boost but you don't have the throttle body open wide enough to allow all of the air in thus the bypass/blow off valve opens to allow the extra pressure vent back to the intake stream (bypass) or atmosphere(Blow off).

I believe when the solenoid is closed the pressure is built up and the wastegate is closed when the soleniod is open the waste gate is open. That is why when you are tuning a EBC (electronic boost controller) you want to have a lower duty cycle or open for a shorter amount of time.

I guess think of it this way the waste gate is like your arm from your hand(wastegate acutator) to your elbow (wastegate) with a pivot point in the center. If you push your hand one way it will push your elbow the other. There for the pressure when the solenoid is closed there is pressure against your hand but when it is open there is pressure against your elbow (from the exhaust gases)

Hope this helps. BTW if I am wrong correct me.

-skooter

 

So if you have enough exhuast to build full boost at 2500 to 3000 rpm, then why doesn't it just build full boost? In other words, what makes the bov vent off the boost to not let it build up to peak boost?