Wastegate crack open pressure

[maxiz1]

Hi guys,
I've been suffering from relatively low boost. Just realised it upon installation of a boost meter and cross checked the accuracy with an industrial pressure gauge. I could never go beyond 6.5 psi. I'm running stock APU (or ATW equivalent).

I've checked almost everything and confirmed to be ok. Boost/vacuum leak, N249, N75, diverter valve.

When testing the wastegate, I observed that it started to crack open at 3.6 psi, and fully open at 9 psi.

I just wondered whether this is the correct setting. Seems to be quite low to me. A few years ago I've sent the turbo for rebuilt and not sure whether the guy had messed up with the wastegate shaft setting.

Hope to see your inputs!

[walky_talky20]

6.5 psi is correct. Spec if only 7psi for ATW.

Wastegate crack pressure is 2-3 psi when stock. I cranked mine up to 5psi crack pressure and it definitely makes the boost behave differently. Like it is harder for the ECU to control it, especially on part throttle where its trying to hit specific, low amounts of boost. I would say yours seems perfectly adjusted.

Have you logged Actual vs Requested Boost and N75 Duty Cycle on a 3rd gear Wide Open Throttle pull from 1500 RPM to redline? I would suggest this.

[maxiz1]

Thanks walky. I was almost going to buy a set of turbo gasket to tune the wastegate. I guess everything is fine so my next step is to get an ECU tuning.

[Blazius]

Probably is yes. And yes the tighter you set the WG , it will be harder to control on those low pressures and areas where you need to control boost with throttle plate is defined, so if you change WG around it wont be the best thing :)

[walky_talky20]

Thanks walky. I was almost going to buy a set of turbo gasket to tune the wastegate. I guess everything is fine so my next step is to get an ECU tuning.

FYI, you can adjust the wastegate without removing the turbo. Here are some notes I made last time I did it:

So I had to replace my turbo>downpipe gasket today. "While I was in there" I decided I would "cowboy up" and check/adjust my wastegate as well. I successfully adjusted my wastegate to 5psi crack pressure *without removing the turbo or exhaust manifold*. The procedure was as follows:

- cowboy up
- remove 3 nuts holding downpipe to the turbo
- unbolt downpipe mounting bolt to transmission
- push downpipe off the turbo and down a bit to create some room
- loosen pinch clamp slightly and pull pressure hose off the wastegate actuator
- connect metered pressure supply to the actuator
- determine the current crack pressure (when you are able to spin the flapper)
- pressure up to FULLY EXTEND the actuator rod
- remove the adjustment nut clip (mine did not have this)
- Use a 10mm deepwell socket (1/4" drive), extension, and ratchet to loosen and remove the end nut from the rod.
- spin the other nut up the shaft with your fingers (mine wouldn't move by hand, so I had to do these next 3 steps)
- hold the flapper open and remove all pressure from the actuator
- slip the rod on top of the flapper lever, pressure it up again (fully extend)
- Use the socket/ratchet to tighten the inboard nut and move it up the shaft a few turns
- remove pressure, slip the rod back into the lever arm hole, pressure up again, install end nut snug (but not tight)
- test new cracking pressure (repeat above steps again if it isn't right)
- Use socket/ratchet to fully tighten the end nut and install the clip
- reconnect the pressure line to the wastegate actuator, pinch using long side cutters
- put your downpipe back on
- cowboy down (?)
- done

I adjusted mine to crack at 5 psi. It was previously adjusted to about 3 psi. It took maybe 2 or 3 additional turns of the nut.

[maxiz1]

That's very helpful walky. For now I'm good about confirming the correct WG setpoint. I did ran the boost log and there seem to be a difference of 1.5 psi less at peak boost (8psi requested vs 6.5 psi actual). I could not simultaneous get the N75 duty cycle due to my scan tool limitation but all in all I think it is ok as an ECU tuning is needed to get a major upgrade in performance. I did not ran it up to the redline coz I'm still with the stock auto tranny and it's making a jerk on downshift. Planning to repair that using transgo kit.

I've one question about the DV. I've read people upgrading the DV to stiffer spring when increasing the boost. However from my understanding, I don't think it is required because the factory installation of the DV has the side to be installed on the turbo pressure side. So the pressure will only exert the piston sideways and in no way will lift the piston even if you don't have the equalisation from the top sensing line. Leaks can only happen if the seal is not good but not really a major leak.

If people reverse the installation i.e. bottom connection installed into the pressure side then there is a possibility of lift but still very small due to the equalisation from the sensing line. In summary, I fail to understand why an upgrade is needed unless you want something more reliable i.e. longer lasting and sealing well. Please let me know if I understand this incorrectly.

[Blazius]

That's very helpful walky. For now I'm good about confirming the correct WG setpoint. I did ran the boost log and there seem to be a difference of 1.5 psi less at peak boost (8psi requested vs 6.5 psi actual). I could not simultaneous get the N75 duty cycle due to my scan tool limitation but all in all I think it is ok as an ECU tuning is needed to get a major upgrade in performance. I did not ran it up to the redline coz I'm still with the stock auto tranny and it's making a jerk on downshift. Planning to repair that using transgo kit.

I've one question about the DV. I've read people upgrading the DV to stiffer spring when increasing the boost. However from my understanding, I don't think it is required because the factory installation of the DV has the side to be installed on the turbo pressure side. So the pressure will only exert the piston sideways and in no way will lift the piston even if you don't have the equalisation from the top sensing line. Leaks can only happen if the seal is not good but not really a major leak.

If people reverse the installation i.e. bottom connection installed into the pressure side then there is a possibility of lift but still very small due to the equalisation from the sensing line. In summary, I fail to understand why an upgrade is needed unless you want something more reliable i.e. longer lasting and sealing well. Please let me know if I understand this incorrectly.

Because that trend started when people didnt really know why Bosch and Audi made certain things the way they did. It was just plastic vs metal, lets gooo upgrade. Even though metal piston DV'a arent really upgrade, because they always leak, it might be 0.1% it might be 0.01% or 10%. A GOOD 710P will hold all the boost you can throw at it with these small frame turbos.
Same thing with the N249. Its there for a reason, to protect your turbo and give it more life and to operate the car at best possible scenarios when certain variables are met. If you wanna do away with all that you can upgrade an electric DV but it requires ECU tuning and some wiring, but that is the next step.

[maxiz1]

Because that trend started when people didnt really know why Bosch and Audi made certain things the way they did. It was just plastic vs metal, lets gooo upgrade. Even though metal piston DV'a arent really upgrade, because they always leak, it might be 0.1% it might be 0.01% or 10%. A GOOD 710P will hold all the boost you can throw at it with these small frame turbos.
Same thing with the N249. Its there for a reason, to protect your turbo and give it more life and to operate the car at best possible scenarios when certain variables are met. If you wanna do away with all that you can upgrade an electric DV but it requires ECU tuning and some wiring, but that is the next step.

I agree with you. My stock DV is still working fine after 20 years and it is still holding pressure when I tested up to 14 psi. Coincidentally I also worked in the consulting industry dealing with pressure relieving valves. But again, if there’s something new I’m more than willing to learn.