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2G Over boost or just paranoid?

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spyderdrifter

10+ Year Contributor
5,263
708
Jul 11, 2009
Somewhere in, Colorado
Here's the symptoms, I'll be driving to work in my usual spirited manner and after the first 5 or so miles of running/boosting fine, it'll over boost. I'll be steadily climbing in boost and then around 5 psi it'll quickly rise to 10 psi. I've seen it go to 12 psi at times too. I'm not too worried about this since 10 psi is factory spec, but is this really ok to live with for now? All my mods are current on my mod list. I don't remember when exactly this first started, but I know it never happened before last summer when I installed my Apexi exhaust (full 3in turbo back - no cat). Still factory fuel system, no mbc, no boost controller, big T28-internally gated, no porting. Like I said, I'm not overly concerned since it doesn't go past 12 psi (prosport Evo boost gauge), but would still like to find out more to this beyond the posts I just read.
 
Sounds like boost creep caused by the addition of the 3in exhaust. As long as it's only creeping to 12psi I wouldn't worry about it, but that's what is happening.
 
I know this was last touched on earlier this year, but I do t want to start another post when I got this here and still this issue. Anyway, I pulled my fmic off and put the smic back on. The fmic will now be going on my gsx. So the smic is on and still I'm over boosting when I shouldn't be. Yes I do have a turbo-back 3 inch exhaust, but I never had over boost until adding the fmic, and theoretically, since it's off, I shouldn't be having over boost. Anyone got ideas?
 
Boost creep is a function of inefficient wastegate not an fmic. And from your earlier posts 10 psi is not factory spec.
 
My wastegate works just fine though and I never saw issues until adding the fmic. I should probably port the compressor housing for the wastegate flapper, but haven't had time to do it.

How is 10psi not factory spec? Thought that was spec.
 
The fmic could cause issues becased you increased the flow through everything. you want to port the turbine housing. Not the compressor housing.
 
Yeah I meant the turbine housing (hot side). So what could cause over boost when everything has been returned to the previous setup when over boost wasn't present? Could it just simply be the turbine housing needing the extra attention? Now that I think about it, I do now have a tubular exhaust manifold too, whereas I didn't the last time I had the smic installed.
 
What a surprise, exactly the answer I expected. You dont have to port the turbine housing. You have to port the wastegate hole at a minimum. Turbine inlet is optional although a good idea.
 
The wastegate hole on the turbine housing is the spot I've been talking about. But that aside, how/why is it being cold affecting this issue? I've lived in Colorado for many years with this car and never had the issue til this year. And last year was by far way colder than now.
 
I got 12 psi back during warmer weather and when the fmic was on. Not so much now, but I still get the sudden increase of boost and rpms when hitting 3-4k rpms. And it'll easily jump up 2k rpm. If it's not boost creep, then what else could it be. Not arguing with what you're saying, but to me it'd make sense that any sudden unwanted jump of boost would be over boost regardless of the psi. Just my thought of it though. Correct me if this is wrong though.
 
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