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2008 Forester 2.5XT
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828 Posts
Discussion Starter · #1 · (Edited)
I've been meaning to post this for a while so here it goes..

On my last 2 open source tunes (with GRimmspeed boost solenoid), I've noticed that 10%-15% throttle will take me to full boost, 24psi. On the Protunes before that with the stock solenoid I would have to give at least 40-50% throttle to do so. My tuner said the GS solenoid can bleed boost much better hence it's tuned this way.

Does this about right?

It just makes me wonder how much more power the car makes at full throttle if full boost is hit at 15% throttle.
 

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Pleiads' biggest leghumper
04's 2 FXT's.
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9,263 Posts
no & he is bs'ing you.He needs to learn how to tune & turn the boost down.It can be done for throttle position & I bet he does not know how.


joe r
 

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2004 Subaru FXT MT
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1,841 Posts
Might want to post a link to your mods and tuning history. If I remember right, you on a VF48 with supporting mods, and on E85, right?

To back Joe up, two things come to mind...

1) Throttle mapping. How aggressive is the throttle mapping? Is it stock?

2) Boost mapping. Boost is mapped against rpm and throttle position. Also, WGDC is mapped against rpm and throttle position. I'm going to guess that your tuner didn't bother to do any mapping in the lower throttle regions, and just punched in 0% DC in those cells. This means that with the GS BCS, the WGA isn't seeing MAP, and the turbo is just going to do what it wants, uncontrolled. This is ok on a larger turbo where the engine isn't supplying enough exhaust energy at low throttle to spin it up too fast, but not on a VF48. The VF is still a small turbo for the 2.5L.

FYI, this is why I don't recommend a MBC as well. You can't control the turbo very well in low load conditions. Make the accelerator pedal feel like an on/off switch.
 

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2008 Forester 2.5XT
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828 Posts
Discussion Starter · #4 ·
I was on a VF48 with everything below. The latest mod is the 20G.


20g td05 with 8 cm
Hi flow X pipe and PnP manifolds
Perrin Turbo inlet
Cobb turboback
Perrin Fuel Rails
DW 1000cc injectors
CObb SF airbox
TurboXS tmic
GS Boost Solenoid
E85
 

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2004 Subaru FXT MT
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1,841 Posts
I was on a VF48 with everything below. The latest mod is the 20G.


20g td05 with 8 cm
Hi flow X pipe and PnP manifolds
Perrin Turbo inlet
Cobb turboback
Perrin Fuel Rails
DW 1000cc injectors
CObb SF airbox
TurboXS tmic
GS Boost Solenoid
E85
At what rpm are you getting 24 psig at 10-15% TP? Do you happen to have a log?

I'm a little surprised that this is happening on a 20g 8cm.

I really need to measure exhaust pressure on our motors. I've had the feeling even the 8cm is too small and is plugging things up, but I don't have any data. The plus side to a small turbine housing is quick spool, which can generate issues like this...
 

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2,132 Posts
Make sure your boost/vac hoses are hooked up correctly. Sounds like they could be reversed so and your wastegate is not opening.

I know this because I hooked up my Prodrive wrong and hit 24PSI at part throttle once... Lucky I'm conservative with timing and had the sense to back off when the boost alarm went off and my butt dyno went off the chart... The car took off super hard though. =)

EDIT: Why the hell is your BCS in a bleed mode? It should not be and should not be tuned as such.
 

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2004 XT
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3,203 Posts
I was on a VF48 with everything below. The latest mod is the 20G.


20g td05 with 8 cm
Hi flow X pipe and PnP manifolds
Perrin Turbo inlet
Cobb turboback
Perrin Fuel Rails
DW 1000cc injectors
CObb SF airbox
TurboXS tmic
GS Boost Solenoid
E85
someone needs to update their signature.
 

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05 FXT
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1,540 Posts
I'm going to suggest a different possibility.

I've noticed that some OTS tunes and some tuners throw crazy high WGC's in at low RPM in an attempt to improve spool. And as your tuner suggests, the GM one will bleed off boost better than the OE BCS. W/ that said, he should have gone back and remapped those lower areas. Apparently he did not.

Isn't this the second post regarding issues w/ your most reason tune?
 

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2004 Subaru FXT MT
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1,841 Posts
I'm going to suggest a different possibility.

I've noticed that some OTS tunes and some tuners throw crazy high WGC's in at low RPM in an attempt to improve spool. And as your tuner suggests, the GM one will bleed off boost better than the OE BCS. W/ that said, he should have gone back and remapped those lower areas. Apparently he did not.

Isn't this the second post regarding issues w/ your most reason tune?
Hum, I didn't catch that it was a bleed setup. I'd really like to know why you would bother going to a different bcs and stay in bleed mode...

If the stock bcs isn't bleeding off fast enough for you, go with a smaller restrictor orifice.

If there is something I'm missing here, please let me know...
 

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2008 Forester 2.5XT
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828 Posts
Discussion Starter · #10 ·
I contacted my tuner and he is going to send me a tweaked map. I'll post up the results.
 
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