Boosting problems with RB25 neo and hybrid/custom turbo?

[Triallity]

I just got my car dyno'd and it has an uncontrolled boost spike to 20+ psi when using electronic boost controllers. My integral EBC to my Apexi Power FC can't control it and a Blitz EBC can't manage it either. When using an MBC to set the boost it just spikes to what you set it at and then tapers all the way to my wastegate (7psi). I was having trouble with this taper on my first tune a year ago but it wasn't such a steep decline. I've tried to adjusting the waste gate preload higher and nothing changes. Heres a link to recent thread of my work/mods up to the dyno.

http://forums.gtrcanada.com/gts-tech/64063-er34-barely-starts-then-stalls-rb25det-neo-apexi-power-fc.html

Also here are the dyno graphs from the first tune and the current one.



This is current one and I have no boost controller on it, just the feed hose straight to the waste gate.



This was from a year ago and is using the integrated apexi ECU EBC.

Now as for the turbo I can't identify what it size/model/spec it is. The numbers are on the compressor housing are 49179-53030, 49178-05120 and 971118033. I google these numbers but the best I find is 18g-20g td05-td06.




Here is the rear of the turbo I find it odd the waste gate is kinda blocked off compared to stock turbine housing and has to flow down at a 90 degree angle to the down pipe.

Does it seem this turbo is wrong for my car and now with cams and thicker head gasket I'm out flowing it? Can I try heavier waste gate spring or is there a controller setup that can hold the boost consistent?

[Skym]

That's normal for RB25DET, RB30DET engines when they create more exhaust gas.

With boost spike the internal wastegate is too slow to react / open the wastegate flap on the back of the turbo hence the wastegate opens slowly and not enough to dump enough exhaust gas in the exhaust housing, which is still driving the exhaust wheel and you get a boost spike. It's common with internal wastegates (they have their limits).

Most boost controllers have a map sensor that can detect and reduce this boost spike (can drop the boost level by opening the wastegate way before it reaches peak boost). HKS EVC is one boost controller that has this feature and I think Blitz boost controller does as well. Apexi has boost level in each gear to gain maximum traction (good for drag racing).

The answer is to bore out the existing wastegate hole on the exhaust housing and fit a bigger wastegate flap to make it vent more exhaust gas or upgrade to an external wastegate with a bigger diameter hole, etc.

Another option is to change the exhaust housing to one that has a bigger flap.

This man goes through the different wastegate options, causes of boost spikes and probably explains it better than I could -

https://www.youtube.com/watch?v=PA5T5PnWE-k

With turbo, years ago Greedy / Trust made bolt on turbo kits using Mitsubishi turbo's (TD06, TD05, etc) with custom exhaust housing to suit, oil feed parts, etc. I think Greedy still sell some of these kits (TD06) but with top mount equal length exhaust manifold, etc that work with aftermarket cams from Greedy / Trust.

Most likely those part numbers are Greedy / Trust part numbers. Would need the Greedy / Trust online catalogue or printed catalogue (Greedy / Trust dealers have these) to determine if it is one of their turbo kits.

These days you can buy Kinugawa Turbo's which are a similar bolt on kit (Mitsubishi / Garrett turbo parts) -

http://shopping.kinugawaturbo.com/turboparts.aspx

They might run similar size exhaust wheels, housings (never compared them).

[Triallity]

That explains my problem I'll just keep it at wastegate pressure for now. The turbo really just seems to be steel wheel'ed stock replacement and probably isn't suited to the cams and thicker headgasket.