Wastegate - need to confirm my thinking.

[Juffa]

So, I have been doing some reading regarding Turbo Wasegates.
To summarise;

• The wastegate actuator controls the level of boost by opening the wastegate to divert exhaust gas away from the turbine.

•This is achieved when the pressure supplied by a hose between the actuator and a pressure source such as the turbine or throttle body overcomes the resistance of a spring in the actuator causing the actuator arm to extend, thereby opening the wastegate.

•The wastegate is available with various spring tensions to allow you to choose the most appropriate for your requirements, and more specifically to protect your engine from destructive boost levels.

•A boost controller can be used to control the level of boost by bleeding pressure from the actuator, thus delaying the opening of the wastegate.

•A boost controller can only raise the level of boost, not lower it.

Please correct me if I am wrong as the above leads me to the following;

I suspect that my current wastegate is designed for around 9-10 pounds of boost. In the short term I was looking for around 6 pounds of boost while I get used to the turbo, ensure the intercooler pipes are tight, and the ECU config is set up correctly for boost. Once I am happy with this I will use the boost controller to raise the level of boost as described in the points above.

Assuming I am on the right track I believe that my only option to lower the boost is to get another actuator designed for a lower boost level. Am I correct in this thinking?

J

[Garry]

Yes your thinking is correct.

If the bracket is shimmed you can try using shorter or longer shims, depending how the bracket is set up. Otherwise you could try bending the actuator bracket ie move the canister closer to the wastegate. This has the same effect. You only need to bend it a few mm to go from 9 to 6 PSI.

[Juffa]

Yes your thinking is correct.

If the bracket is shimmed you can try using shorter or longer shims, depending how the bracket is set up. Otherwise you could try bending the actuator bracket ie move the canister closer to the wastegate. This has the same effect. You only need to bend it a few mm to go from 9 to 6 PSI.

Thanks Garry ,
The bracket isn't shimmed. I will give the bracket bend a try.....

J

[sabretooth]

I don't think I can add much here, except a \"Yep, what Garry said\".

[Techno]

Hi Jeff,
Where are you taking the line to the actuator from .... before or after the intercooler?

How accurate is your reading?

Most actuators have a 7psi default and the actual boost is controlled by regulating the flow in the line.

[Juffa]

Hi Jeff,
Where are you taking the line to the actuator from .... before or after the intercooler?

How accurate is your reading?

Most actuators have a 7psi default and the actual boost is controlled by regulating the flow in the line.

Rob,
Currently taking the line from the before the intercooler. Looking to take it from after the intercooler, ie the throttle body.

Are you free to take a phone call on the weekend about this?

J

[sabretooth]

Post-intercooler will effectively run an even higher boost level. The pressure drop caused by the intercooler will in turn result in the wastegate seeing a lower pressure.

[Garry]

What Sabre said

[Juffa]

In order to test what the pressure required to extend the actuator arm is, I bought fishing hand held scales. The idea beng that I would attach the scales to the actuator arm and pull on the scales until the actuator arm extended and take a reading of the amount of tension on the scales.



I needed to pull the actuator and arm off the turbo to give myself enough room. As you can see I put the actuator into my bench vice to hold it. It required around 12-13 pounds of tension before the arm started to extend. So I'm assuming that my actuator is not opening the wastegate until around the 12-13 pound mark. The MAP sensor is reading around 9.5 pounds at the throttle body. I disconnected the boost controller. Reinstalled the actuator, and connected it directly to the nipple on the turbo body. I then took her for another run and confirmed that boost is maxing at around 9.5 pounds at the throttle body.
I am thinking inthe short term I will bend the actuator bracket by a couple of MM to reduce the amount of movement required by the actuator arm to begin opening the wastegate. In the long term I will probably buy an adjustable actuator, such as the one from Flyin Miata. Thatparticular one can be adjusted between 6 to 9 pounds.

J

[The Pupat]

Juffa: doesn't work like that ;)

The better way to test what pressure it opens at is to rig up a bicycle pump to the pressure line the pump it till the actuator moves (though even then it can be hard to say when it would open the valve enough to control the pressure.

Ohh and I personally wouldn't bother with the adjustable wastegate for 3psi of movement. The boost controller should be enough I'd think (depending upon what type you got).

[Moggy]

I needed to pull the actuator and arm off the turbo to give myself enough room. As you can see I put the actuator into my bench vice to hold it. It required around 12-13 pounds of tension before the arm started to extend. So I'm assuming that my actuator is not opening the wastegate until around the 12-13 pound mark.

This doesn't sound quite right. The scale reading is in pounds, while the pressure on the wastegate actuator is felt in pounds per square inch. So to work out your wastegate actuators opening pressure, you would need to know the area of the diaphragm inside the wastegate actuator and then calculate the pressure required from that.

The wastegate opening pressure would definitely be below 12-13 psi as the diaphragm area would be above one square inch.

It would be unusual for a stock wastegate to boost that high without a bleed (but possible, of course). Perhaps as it is quite a small turbo it is designed to not run low boost? Or maybe something is not set up exactly right. Is the wastegate actuator arm under tension when you bolt it to the side of the compressor? Perhaps the wastegate actuator is having to overcome more than just spring pressure... Also any leaks in the wastegate sensing line will cause an increase in boost.

In the end though, 9.5psi will not cause any harm to your turbo, and in the longer term most people like to run over 10psi anyway... So in other words just go with it...

[Juffa]

Thanks for the responses guys. Do you mean to say I wasted $10.83 on fishing scales Man, this turbo install is breaking the bank

I have attached a bike pump to the actuator. The pump does have a gauge attached, but it was hard to see what the pressure was when the actuator arm moved. Will try again this week.

As for using a boost controller, it my understanding (see earlier part of this thread) that a boost contoller can only raise the boost above the mechanical restrictions of the actuator, not lower it. For instance if the actuator startes to open the wastegate at 9.5 pounds I cannot use the boost controller to lower it to 7 pounds.
I understand that there a low probability that I will damage the engine at 9 pounds of boost, but I would feel more comfortable starting at a lower level of boost and raise it with the use of a boost controller when I (and Tweety) are ready for it.

[Garry]

that a boost contoller can only raise the boost above the mechanical restrictions of the actuator

Yeap.

This is a used turbo so the wastegate may have been adjusted to open at 9.5PSI for the previous application. Just set it to suit your requirements.

[The Pupat]

sorry yep that's true didn't realise that's what you wanted. There's probably a few options to try one of might be might be bending the bracket. They other is having the spring replaced in the turbo if you take the spring out of the actuator and give the Actuator and the spring to a spring maker they should be able to fabricate one at whatever percentage up or down you want, should cost around 60 - 80 dollars I'd say. Otherwise a better place to start would be a garrett retailer (assuming it's a garrett turbo) should be able to supply you with a lower pressure spring I believe. If it's a no go trying to get one from a garrett retailer and you want to try the spring maker route let me know and I'll get you a name to go see.

[sabretooth]

Bending the rod won't change that it opens at 9psi - just that it'd open to 100% quicker when 9psi is reached. Although that theory could be wrong

The helper spring certainly sounds like it'd work to me - and as Warpspeed has posted - it does. The helper spring would mean that less pressure is required on the wastegate actuator's internal diaphragm as pressure is already being applied by the spring. The trick though, would be to get the correct spring rating to create a wastegate that opens at 5psi. Perhaps you can rig up the fishing scales and use those as the helper spring...