all the other ports are plugged except for the top (vent)... and all the lines are the same

 

Remember that a turbo system which consists of a relatively big turbo on a small enigne is like a self feeding monster. It takes a while to get going, but once it does, it ramps up very very quickly.

Hence, when you look at dyno charts of 1000+whp Supras, you get nothing until 5k-6k rpms and then you get a massive massive torque and hp spike in a very short rpm range.

So in your current case, with the wastegates wide open, you can't generate enough flow to get the turbo boosting.

Your wastegate placement is poor, so once the turbo starts to build a head of steam, the wastegates can't properly dump enough flow and you get the massive spikes you saw. That's also why with the 0.5 bar spring, you get a minimum of 19psi. The spring is stiff enough to get the turbo spinning, and once the turbo is up on boost, the wastegate flow paths are too poor to dump off enough exhaust to keep the boost down.

I take it you're trying to run more than 25-26psi? Without making a completely new exhaust manifold, you can try preloading/shimming that 0.5bar spring in the wastegates. It's like the old crushed DSM BOV trick; you preload the spring a bit so it takes more force to open it.

Your boost control is still going to be kinda ****ty, but better than having to make a completely new manifold I think.

 

while the placement may not be great, i think there is more going on. you dont go from zero positive manifold pressure with no gates, to massive spikes unless there are other issues. can we get more pics of all the lines and plumbing? where are you sourcing boost for the boost controller?

 

Sounds like the small head on the wastegate doesn't have enough of a meChanical advantage to open the gates at the proper boost. Then when you have the high back pressure of a stock housing turbo on there the spring can't gold the wastegate closed against exhaust pressure above 25psi. Swap in some full size 44mm wastegates and see how that works.

 

TYou should run boost to the top port with a solenoid to help gold boost up top and have the solenoid cut the boost to the top at target boost

 

Wastegate priority shouldn't be such an issue on a highback pressure strip like a Black. Now on a big turbine strip like a 42R I can see an issue with boost creep since the turbine section is so efficient.

 

The other option would be to do backpressure based boost control. Load the wastegate until it opens at a certain pressure on the valve seat and rock it with no boost reference.

 

learning

 

Lets be real here...I've seen way worse gate placement on bigger turbo's not have problems on evo's. I would look elsewhere before focusing on that.

 

they aren't trying to control low boost....

 

that generally indicates too much gain on the boost controller

 

Ok lets back track a bit... I understand what you were thinking about the turbo but here is the reality.

I have a .5 bar spring in the wastegate (yellow)... When i hooked it up to a leakdown tester with the wastegate in my hand... (off the car).. The wastegate fully opened at 19psi. I wrote this on the original post and people still keep thinking it is the manifold.

 

because there is no force on the valve head itself from the exhaust gas

 

OK. so now what do i try?

 

you can try the lightest spring possible, but what really needs to be done is getting better priority to the wastegates