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Boost drop with V3 BCS - Evo316g

tsitalon1

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Dec 29, 2010
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309
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Montgomery Al
Nope - There are two small cracks that were previously welded up before I acquired the manifold.

I do not see any carbon around them so I don't "think" they are leaking.

Do Evo316g turbo's sometimes suffer from the old problem where the wastegate flapper valve comes off center allowing some bleed off? Would I still be able to spike to 25-27psi if that were the case?
 

Barnes

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Feb 9, 2003
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Richland, WA
I could see that. Happen to my 14b, and I think it's the same mechanism. Take a picture of the flapper arm where it goes into the exhaust housing. maybe your bushing is sliding out.

Reason I ask about the EGT tap was to see if you could put a nipple onto it and attach a boost gauge. Might be handy to measure turbo back-pressure.
 

prove_it

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Jul 3, 2008
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Sioux Falls, SD
Wouldn't that burn out the gauge?

Also +1 for a sticking housing arm. My cheap ebay housing did that. Would not boost over 10 psi as it would stick.
 

Barnes

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You just have to run a long line. No exhaust gas flows into the boost gauge. It just pressurizes the air inside it. Well, as long as it isn't leaking internally. /ubbthreads/images/graemlins/uhh.gif
 

Boos929

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Feb 17, 2012
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Mass
my 14b does this also if I go from a stop I can only boost 10 psi but if I cruise at like 3k and get on it it will go up to like 13-14 psi but will only hold for a few k before boost drops back down to 10 psi. what does shimming the wg entail ? sorry for the newb questions
 

tsitalon1

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I don't have the same symptoms the posters above are talking about..

I can easily spike to 25 or more and hold it to 5-5.5k - Then it drops to 18-19 by redline
 

tsitalon1

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Montgomery Al
Update: With exhaust removed (everything behind the downpipe)boost levels have not changed at high RPM - Still dropping to 17-19psi at redline.

@prove_it - I will get a log for you shortly, though I can tell you I'm around 35 lb/min according to EcmLink at 6500rpm.

Now I got to get that exhaust back on...it's damn loud without /ubbthreads/images/graemlins/smile.gif
 

prove_it

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Sioux Falls, SD
What are you basing the boost drop on? The boostest? I see you don't have a MAP sensor, so was wondering.

Also you are using the ecmlink boost control right? I see it's active and I'd like to know how you plumbed the controls. I suspect there maybe an issue there.
 
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tsitalon1

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Dec 29, 2010
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Montgomery Al
No Sir, boost drop is based on my boost gauge tee'd into my BOV line. I fully understand boostest is not accurate at higher rpm's.

BCS is connected as per ECMLINK wiki page which is a bleeder setup if I'm not mistaken. To ensure it wasn't my BCS I fabricated a MBC and the results were identical.

My only guess now is that the exhaust manifold has a crack on the bottom of it that isn't visible while installed. I've obtained a 2g manifold and will port it and the o2 housing and see what happens.

Any other ideas?
 

prove_it

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Have you checked and made sure it's a true 7cm exhaust housing? What cams do you have? Your getting 35lbs/min. 42 will be about the peak of your 16g. Boost pressure and airflow are completely different. Your actually not that far off from maxing it out. Airflow can stay the same as the pressure falls. There must be an airflow restriction occurring somewhere, that's all I got. It might just be the stock manifold and O2 housing. I never pushed a 16g with stock stuff, so not sure if that would do it.

I'd make sure your exhaust leak free pre turbo, and also make sure you have a 7cm exhaust housing. Never know.

And since your trying to max the 16G, I would get a capable manifold and housing anyway. Toss the stock crap.
 
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tsitalon1

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Dec 29, 2010
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Montgomery Al
Thanks for the input - Yeah I've never ran a 16g with stock stuff before either. My many DSM high HP builds in the past have swayed me to keep the GVR4 simple and as streetable as possible. To me that means small frame turbo and maxing out what I have rather than slapping a large turbo on and dealing with the lag that is usually associated with it.

I'm not overly familiar with the Evo316g so what am I looking for to determin if it's a 7cm housing vs 6cm?

I know 35 lbs/min is fairly close to maxing it...but if I'm not mistaken there should easily be another 40-50hp available from my setup.

I'll try porting the hell out of the 2g manifold and stock 1g o2 housing since I already have them and see what happens.

I appreciate your time and thoughts!
 
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tsitalon1

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Dec 29, 2010
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Montgomery Al
Alright, here's what I tried that made zero difference:

Replaced stock 1g manifold with a ported 2g manifold
Ported Turbo turbine housing
Ported O2 housing.
All exhaust gaskets replaced.

No change in high rpm boost drop from 25 to 18-19.

I think it's directly related to the Evo 8 FMCI I installed.

I used many reducers to install the FMIC in order to utilize the stock IC piping. My current IC pipe setup is 100% OEM except at the FMIC where it enlarges to 2.5" to accommodate the FMIC. There is also a pretty tight 90º turn on the drivers side entering the FMIC.

So, my question to you guys is, can diameter changes in IC pipes cause pressure loss?

Or can the stock Evo 8 FMIC not support high rpm high boost (25+psi)?
 
Last edited:

slugsgomoo

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Oct 16, 2003
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Tacoma, WA
the evo fmic supports that kind of boost on an evo, so I doubt it. I assume you've pressure tested to at least 30psi?

I'm kind of wondering if where you're sourcing your vacuum line is the issue, I know you aren't supposed to run the AFPR off the BOV line because it can bleed pressure. Have you considered running a dedicated line from a manifold source to the MBC?

Alternatively, if you want to live dangerously unplug the wastegate and see if it'll hold boost that way. I'd expect a spike to 29-32psi and then it should taper to redline, but frankly on pump gas you'll knock like crazy if it actually holds. If I had to bet, I'd guess the BOV is bleeding some pressure and causing the misbehaving.
 

tsitalon1

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Dec 29, 2010
Messages
309
Location
Montgomery Al
I have pressure tested the system to 25psi and cannot locate any leaks, even put my ear to the BOV.

I use to have the BCS source line from the turbo outlet pipe, but moved it to the BOV line, nothing changed.

I really think it's the FMIC setup because if I recall correctly I was able to hold 21 psi to redline with the factory IC and HALF of the WG duty cycles in the past.

Not sure what to do at the moment - I threw out the oem IC so there's no going back /ubbthreads/images/graemlins/smile.gif
 

slugsgomoo

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Oct 16, 2003
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My evo3 was able to hold 24psi to 9,000 rpm with a much bigger intercooler than an evo core (24x12x3.5), I think your issue lies elsewhere, have you tried running unplugged just to see what happens? If you can't hold boost with it unplugged either you have big leaks, your wastegate is toast, or the turbo is not well IMO.
 
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