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Old 01-17-2007, 03:10 PM   #1
wrxfactor
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Member#: 49978
Join Date: Dec 2003
Chapter/Region: NESIC
Location: Shrewsbury, MA
Vehicle:
2002 WRX w/ JDM STi
6spd, EJ255, VF39 & EWG

Default Is my WGDC affecting max boost? EWG VF39 2.5L 02 WRX

Here is my problem: I had a Bosal twin dump DP mated to the stock 3rd cat from an 02 WRX. At 20psi with all the below mods (before HKS DP) the car made 220whp and 240wtq. 20psi was the max that the turbo could make, and the shop suggested backpressure was an issue. The wastegate was fully shut, and yet the turbo could make no more boost. They attributed this to the cat creating excessive backpressure.

About a week ago I swapped the Bosal/3rd cat combo in favor of an HKS DP. Now I am only seeing 11psi at WOT in 3rd gear, and 12psi at WOT in 5th (100mph or about 4100-4200RPM). So here are my questions:

1. Could the issue of backpressure have forced my tuner to give uncharacteristic WGDC values that are now preventing me from making more boost?

2. If not, what could be preventing me from making boost? Leaks might be possible, but it was immediately after the downpipe swap and I am sure nothing was bumped.

3. Would using an MBC in place of the stock BCS allow me to figure out if I can make more boost, and is this a reasonable solution in the short run?

I know that info is needed to answer my questions, so here's the mod list:

USDM Legacy GT EJ255 engine swap (full longblock minus intake manifold and throttle body, no AVCS hooked up)
SSAC top mount intercooler
EcuTeK flash on 2002 WRX ECU
Seimens 660cc injectors
Walbro 255lph fuel pump
UR EWG uppipe
TiAL 38mm WG
VF39 with welded flapper
HKS heat-coated DP
Stock 2005 WRX catback


Something else I feel should be mentioned. At 11psi in second gear, the butt dyno feels the same power as it used to feel at 18-19psi. My guess is that the tune had headroom and now the car is making some more power, but I am not sure how much more.
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Old 01-17-2007, 10:13 PM   #2
wrxfactor
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Member#: 49978
Join Date: Dec 2003
Chapter/Region: NESIC
Location: Shrewsbury, MA
Vehicle:
2002 WRX w/ JDM STi
6spd, EJ255, VF39 & EWG

Default

I will answer myself as #3 was performed tonight and we reached 20psi without issue. This should be fine in the short run, we didn't set it close to 20 psi, rather around the 14psi mark. Also, it's 18 degrees F out tonight, so it should be a tad less in warmer weather.

My assumption in #1 was most likely correct. By eliminating the use of the stock BCS, we cured the inability to make boost. Therefore, this is a tuning issue, not a mechanical one. We don't need to address #2.

It's alright that no one responded and made a suggestion, I just hope that this will help someone in the future who may run into the same or a similar problem.
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Old 01-18-2007, 08:40 AM   #3
blkscooby
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Location: Gilbert, AZ
Vehicle:
2009 G8 GT
Cammed, sprayed, stalled

Default

Quote:
Originally Posted by wrxfactor View Post
I will answer myself as #3 was performed tonight and we reached 20psi without issue. This should be fine in the short run, we didn't set it close to 20 psi, rather around the 14psi mark. Also, it's 18 degrees F out tonight, so it should be a tad less in warmer weather.

My assumption in #1 was most likely correct. By eliminating the use of the stock BCS, we cured the inability to make boost. Therefore, this is a tuning issue, not a mechanical one. We don't need to address #2.

It's alright that no one responded and made a suggestion, I just hope that this will help someone in the future who may run into the same or a similar problem.
You may be premature in your conclusiopns about #1 and 2. I have found on a friends car that the stock BCS is limiting him to 19 psi boost. I have the GM BCS in my car and I can make up to 22 out of my TD-04. I think that the stock BCS cannot overcome increased boost pressures above 18 or 19. This would then cause the boost pressure to begin bleeding away and not increasing. I would suggest the GM BCS; its inexpensive, easy to do ,but would require your WGDC map to be lowered. It requires about 40% less DC because it is a stronger solenoid. I am not sure how it would work on a EWG setup though. I'm sure someone else has tried it?

Also, are you using a stock, unmodded BPV? If so, that could also be part of the issue. THey are known to not hold boost above 18-20 psi. They can be modded for $0.16 (search thread) and hold much more boost.
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Old 01-18-2007, 12:02 PM   #4
wrxfactor
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Member#: 49978
Join Date: Dec 2003
Chapter/Region: NESIC
Location: Shrewsbury, MA
Vehicle:
2002 WRX w/ JDM STi
6spd, EJ255, VF39 & EWG

Default

Quote:
Originally Posted by blkscooby View Post
You may be premature in your conclusiopns about #1 and 2. I have found on a friends car that the stock BCS is limiting him to 19 psi boost. I have the GM BCS in my car and I can make up to 22 out of my TD-04. I think that the stock BCS cannot overcome increased boost pressures above 18 or 19. This would then cause the boost pressure to begin bleeding away and not increasing. I would suggest the GM BCS; its inexpensive, easy to do ,but would require your WGDC map to be lowered. It requires about 40% less DC because it is a stronger solenoid. I am not sure how it would work on a EWG setup though. I'm sure someone else has tried it?

Also, are you using a stock, unmodded BPV? If so, that could also be part of the issue. THey are known to not hold boost above 18-20 psi. They can be modded for $0.16 (search thread) and hold much more boost.
I had no problem making 20psi pre-downpipe swap, even with stock BCS and unmodded BPV. I have a GM BCS in my back seat but I can't put it in unless I go get retuned. I bought it because my tuner told me to do so, however, when I returned for him to fix the tune, he told me they had solved the problem for someone else with a restictor pill, so we never put it in (to my dismay).

Many people who go to an EWG setup do not utilize the stock BCS, instead they use the GM, Perrin, or Prodrive, or a better EBC like the AVC-R. We are using both ports on the MBC as TiAL suggests in the diagram on their website. Here is how it's set up:



The only thing we did was eliminate the vent coming from the top port of the WG to the side port of the MBC. Putting a T in there would release too much air, so I will set it up that way when the GM BCS goes in.
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Old 01-18-2007, 12:26 PM   #5
blkscooby
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Join Date: Sep 2003
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Location: Gilbert, AZ
Vehicle:
2009 G8 GT
Cammed, sprayed, stalled

Default

Where is the discharge from your EWG tied in? Or does it dump to atmosphere?
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Old 01-18-2007, 12:38 PM   #6
wrxfactor
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Member#: 49978
Join Date: Dec 2003
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Location: Shrewsbury, MA
Vehicle:
2002 WRX w/ JDM STi
6spd, EJ255, VF39 & EWG

Default

Quote:
Originally Posted by blkscooby View Post
Where is the discharge from your EWG tied in? Or does it dump to atmosphere?
The EWG setup is VTA, I love the sound You shoulda seen the smile on my friend's face when telling his brother how awesome it was. It might n ot be super pratical, but it keeps me from mashing the go pedal quite a bit.
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