When Shoud You Upgrade The Actuator?

[Romulus]

The pressure in the turbine/waste gate housing will determine if the valve needs to be replaced.

Obviously if you up the power you will be increasing the exhaust flow many times over and without a high flowing exhaust the back pressure will build in the Turbine housing and act on the waste gate vale and force it open which in STd form its not a problem.

Increase boost will apply a greater resistance to rotation as this acts on the compressor wheel and as such we require a greater flow to spin the turbine enough to overcome this resistance and in tern increase boost pressure.

Take my F6 for an example... a gain of 4 PSI in boost with the exhaust changed to twin 3.5” and twin cats.

Why? Well simple really and two factors which are simply less resistance to flow and as such the turbine can spin faster and secondly with less resistance to flow than the standard exhaust there is less pressure acting on the waste gate valve trying to force it open. This encourages all the flow then to travel through the turbine wheel and as such it spins up faster producing more boost.

I suppose if you don’t open the exhaust and as such maintain a high resistance to flow then this increase in pressure will require a heavier spring to keep the waste gate closed.

Think of it like this… you have a cork up its ass and as such the exhaust pressure rises and pushes the valve open as the std spring is too weak.

<{POST_SNAPBACK}>

True Greg, but what about the exhaust pressure in the exhaust manifold and the turbo, prior to the gasses exiting the turbo? No matter how big the exhaust after the turbine housing is, there is still limitations trying to achieve higher than stock boost at high rpm.

I've gone down the avenue of replacing the dump pipe and cat, yet the car wouldn't hold more than 12-13 psi boost at high rpm. You'll find your current setup will not hold more than 12-13psi boost at 5500 - 6000rpm with the stock actuator. There is too much volume and pressure of gas between the exhaust ports and the turbine housing for the actuator assembly to keep the wastegate flapper shut. Hence companies like Nizpro recommend changing the wastegate assembly in pursuit of higher boost.

You'll be amazed how well the PCM is able to control boost once the actuator has been replaced

We should give it a go with yours. I recon there's another 20-30 rwkw to be had in your car

<{POST_SNAPBACK}>

I can hear you’re lips Jason.

Think about this one and I’m sure you’ve seen it on my ute as well.

The boost tails off big time as the rpm rises with an F6 tune with an F6 map.

Now when we run the XR6T map in the F6 we could hold the boost up heaps more than the f6 map would and we produced more kws.

Didn’t change any mechanical parts at all.

Then consider if the wastegate is controlling the boost @ 2000rpm with 18psi of boost then there is a lot of boost trying to slow the turbine down and possibly the greatest amount of backpressure in the turbine.

So then @5000rpm we have 12 psi of boost would there not be less resistance to the turbine as there is 8 less psi of boost acting on the compressor wheel.

Even think of it like this:

A turbo is not a positive displacement pump and as such it works better with High flow and velocity not pressure. Unlike a blower which is gear driven.

So to spin the turbine to generate a positive pressure on the compressor side the exhaust velocity and volume will be the main contributing factors not the pressure. To maximize the velocity and flow we need to minimize the resistance to flow…Remove the cork out of its ass.

<{POST_SNAPBACK}>

I hear (read) what you're saying Greg, but the 2 calibrations (F6 vs. XR6T) are different. Without going into detail there are differences in turbo controls which cause the diferences in boost. I wont tell you which tables however......

Changing the actuator has helped my car hold boost at high rpm, something which it wouldn't do before.

Go figure.........

[NighEve]

I have massive problems with control of boost (either surging when it is working half decently, or serious dips and spikes which will not go higher than 10.5psi). I will have an upgraded actuator installed later in the week.... I'll let you know how it goes.

[blueboost]

just be carefull, because if it is not the actuator, your spikes might be higher then before.

David