Greddy type C wastegate, what spring to use?

[Special_K]

So I got my wastegate apart and seems the diaphragm is good afterall. So I'm still trying to figure out why I had boost creeping over 2.0bar.

Would the fact that I have the purple spring (highest available from greddy @ 1.5kg/cm2 21.3 PSI) be a cause? The adjustment screw on top is at the midway point. Which direction should it go if I want to get the lowest boost possible on this spring? I'm assuming 21 PSI is the lowest this spring can do? I'm still learning boost stuff

[r33_gtst]

2 bar of boost as in approximately 30psi ?
What is your set up

[Special_K]

not sure what's usually listed in the setup so I listed all the engine related stuff

rebuilt engine (in Japan) by HRF.
05U block
Weiso low compresion pistons
1.1mm head gasket
272 cams (in and out) 10.8mm lift
JUN oil pump
aftermarket valve springs (not sure what kind)
R33 crank
Greddy intake manifold
Greddy fuel rail
split fire coil packs
Greddy surface fire "10's" plugs
Greddy high capacity sump
Greddy hard pipe kit
RC 1000cc injectors
Z32 AFM's
Greddy Y pipe
Garret 4094R turbo
PLX devices wideband
custom braided oil/water lines for turbo
HKS mushroon filters
Greddy hard pipe
Grex oil filter relocation kit
Greddy oil cooler (I think)
Greddy intercooler (almost 6" thick)
FC datalogit
Power FC with hand controller
Blitz twinSBC boost controller

[Special_K]

Anyone know what size and spring PSI they would normally run in a wastegate for gt4094R turbo? This car originally had a T88 and was swapped for the 4094R to get better spool times with close to the same power.

[r33_gtst]

your problem could be in two places
boost controller not regulating boost properly
single waste gate may not be enough to control that high of boost
If you are running 30+ psi it might be better to go with two wastegates to help control the boost. The new turbo may spool much quicker and the boost controller/wastegate are not equipped for the power.
Id check the boost solenoid and play with the settings
Did you tune the car after the turbo swap?

[Special_K]

the previous owner swapped the turbo but never got it properly tuned. It worked but the flashing knock lights up over 5000rpm so I haven't pushed it hard. You might be right about needing a second wastegate. I'll have to look into this

[Special_K]

update on this.

After some research I seem to understand things better and wanted to to see if others agree.

When I was driving the car home after buying it (5 day road trip) I would lay into it and the boost would build fast from 2500rpm to about 4500rpm and at that point the PFC knock light would flash and the boost would be almost 1.5bar. I'm a bit hazy on the exact reading, it might have been 2.0bar at this point. I just remember being freaked out by how fast the boost shot up and was afraid of blowing the engine. The previous owner said it had a boost creep issue that he thought was because of a cracked header. He's repaired the header a few times.

After I got home I took the exhaust side apart thinking I would find a header leak and that would fix things. But after researching boost creep I found that a leak isn't the cause. It seemed more likely that the waste gate wasn't opening at all since there was no hesitation in the boost building. After taking the waste gate apart I found the spring inside was the biggest offered for this waste gate and this waste gate is one of the biggest greddy makes. The spring is rated at 22psi but the setting screw was half way in causing even more psi so i'm thinking it wasn't even beginning to open until 26-28psi, or about 1.9bar. The boost controller had no hope of controlling boost below 1.9bar since it was physically restricted by the spring.

So basically I need a smaller spring in the waste gate to get to my target boost which is about 1.0bar for now until I know the car better and check over the tune. Anyone else agree?