Can a wastegate flap be pushed open from the inside directly by boost?
 

I'm on the standard actuator spring (probably 7PSI), and with an EBC at 100% duty I'm only getting a max of 12.5PSI.

I read a lot about boost creep on the TD04, so ported my exhaust housing to the wastegate heavily (though did not touch the material that seals with the flap); is it possible that my porting has diverted the gasses so much to the wastegate that the flap is being pushed open from inside and overcoming the actuator spring? Is this a thing?

Yes - depending on the strength of your wastegate spring, your level of boost and the type of actuator - the wastegate can (sometimes) easily be pushed open by exhaust gasses. Your porting might contribute to that, but those other factors might outweigh the porting.

This is my MAP against RPM. My boost solenoid is at 100% duty at the top of the revs but it still won't make more than 12PSI.
https://cimg4.ibsrv.net/gimg/www.mia...7507576d7c.jpg

I'm tempted to tie down my wastegate, gently accelerate to 5000rpm, and then floor it to see if I can make more than 12PSI. This will prove I'm experiencing the exhaust gasses pushing directly pushing the flap, will it not?

Yes, I have the same problem right now...

More preload/stiffer spring is what you need

So if I'm currently making 12 PSI and want to hit 14, what spring rating would you suggest, bearing in mind I do have a boost controller and am probably currently on a 7PSI spring.

Ive heard the rule of thumb is double wastegate pressure is where the exhaust pressure will start forcing the door open.

a stronger spring sounds like the solution.

Hook it up without EBC, or turn EBC off and see what your waste gate pressure is. That will give a better understanding of what is happening, and what spring you actually have now.

Yes, about 2X waste gate pressure seems good for a typical sized, single port can.

If you do wire your WG closed, have Boost Cut set to 14 psi, as well as being careful. The computer is faster than your foot.

DNM

Are you running a vented 3 port ebc solenoid? What and how is your ebc plumbed?

I'm running a Mac 3 port solenoid. I have port 3 to the compressor housing, and port 2 to the wastegate, with port 1 venting to atmosphere.

Unhook and plug the vacuum line running to the WGA, see what happens.

Have you done a boost leak test?

Short answer is, yes, it can get blow open. But I would be surprised if it was that low. My friend had the greddy td04 and it would run 20+ psi with the vacuum line off and it's waste gate would open at like, 5psi normally.

No boost leaks; I got the system to hold 1bar of pressure for quite a while without any leaks.

Perhaps your friend is experiencing what a normal TD04 will do; I have (regretfully) ported my wastegate channel a lot within the exhaust housing.

Interestingly, I have just been for a drive with the EBC switched off, so just wastegate pressure; it now surges rhythmically as you floor it. In the below plot you can see the boost fluctuating. Does this suggest the wastegate flap is indeed being pushed open by exhaust gasses directly, or is this what happens when you exceed the boost pressure of the wastegate spring?

https://cimg9.ibsrv.net/gimg/www.mia...3418234d58.jpg

I switched the EBC back on, and the surging stopped and it pulled as per normal (but still hitting it's 12PSI ceiling despite EBC working at 100%).

You have to see if the system is working correctly at all. Do the above with discconecting the vacuum line from the WGA and see if it blows open. If it does, you know the problem is with the waste gate/too light a spring. If it doesn't, then it's with the EBC.

So I fitted the 13PSI spring and it made no difference.

Then I removed the line to the actuator and tested it with gentle acceleration up to 3500, and then full throttle. It's now hitting the set boost limit (205kpa 15PSI) but tailing off at the top end:
https://cimg0.ibsrv.net/gimg/www.mia...1380b5e19e.jpg

Over 6000rpm plot:

https://cimg8.ibsrv.net/gimg/www.mia...60472ee31a.jpg

Then I kept the actuator off and tied back wastegate:

https://cimg4.ibsrv.net/gimg/www.mia...01556af89a.jpg

You can see it finally holds the boost limit all the way to the 7000rpm, like I've been wanting. So what can we conclude from this? Is this proof the wastegate is being pushed open from the exhaust gases at high RPM?

Update, I wound about 20mm of preload into my actuator and now I'm getting a lovely 201Kpa max, with it holding pretty strong to the redline.
https://cimg9.ibsrv.net/gimg/www.mia...ec235ab419.jpg

Where as with the regular 2mm or so of preload I was getting a max of 185Kpa and it tailed off badly:

https://cimg4.ibsrv.net/gimg/www.mia...bcb64ad177.jpg

Interested to see what happens when you connect the tube back up. Do you have any travel left?

Wait, wait, wait...
are you saying you hit a constant 200kpa or so max with the wastegate wired shut?