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Discussion Starter · #1 ·
which is better? i have a mbc on the car now and it seems to do ok, doesnt hold boost as well as i want. when i had the car pcm controlled it would surge like crazy at 15lbs after the s3 swap, suppose to hold 20. bad solenoid? all vac hoses were and still are hooked up as they need to be, no boost leaks, ran boost leak test.
 

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Two possibilities to consider .

I see you have a hks , but do you still have the stock bov on the s3 compressor housing ? If yes , a bad diaphragm wont show up in a boost leak test unless you have the ricer plate on it .

Exhaust manifold studs tight ? No damage to gasket allowing blow by ?

If you are not holding boost on a MBC then we can rule out the ecu as the culprit . So if you got good results with the boost leak test ( less than 1 psi drop per second every 1.5/2 seconds ABOVE 20 psi ) , then the issue may be on the hot side of the turbo .
 

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Discussion Starter · #4 ·
boost box then pcm boost then mbc..

you have to tell duster you want PCM control boost if your using a different wg than stock s3 one

i did when he did the s3 tune for me. it does fine pcm controlled 1 time then it starts to surge badly. i disconnect the battery reset the pcm and it does good 1 time again and then surge again.
 

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Discussion Starter · #5 ·
Two possibilities to consider .

I see you have a hks , but do you still have the stock bov on the s3 compressor housing ? If yes , a bad diaphragm wont show up in a boost leak test unless you have the ricer plate on it .

Exhaust manifold studs tight ? No damage to gasket allowing blow by ?

If you are not holding boost on a MBC then we can rule out the ecu as the culprit . So if you got good results with the boost leak test ( less than 1 psi drop per second every 1.5/2 seconds ABOVE 20 psi ) , then the issue may be on the hot side of the turbo .
studs are tight, no blow by. turbo has a block off plate, hks bov is on cold side pipe.
 

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Discussion Starter · #6 ·
Two possibilities to consider .

I see you have a hks , but do you still have the stock bov on the s3 compressor housing ? If yes , a bad diaphragm wont show up in a boost leak test unless you have the ricer plate on it .

Exhaust manifold studs tight ? No damage to gasket allowing blow by ?

If you are not holding boost on a MBC then we can rule out the ecu as the culprit . So if you got good results with the boost leak test ( less than 1 psi drop per second every 1.5/2 seconds ABOVE 20 psi ) , then the issue may be on the hot side of the turbo .
mbc holds boost until it gets high in the rpm's. itll spike about 22-24lbs and by 6500 rpm im holding steady at 15lbs.
 

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Discussion Starter · #8 ·
Send dave a log, both when it works right then the next pull on same log of it spiking.

If its a tune issue he will fix it..
i guess i'll hit him up when i can do the log and send it to him. i work all day everyday.
 

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Two possibilities to consider .

I see you have a hks , but do you still have the stock bov on the s3 compressor housing ? If yes , a bad diaphragm wont show up in a boost leak test unless you have the ricer plate on it .

Exhaust manifold studs tight ? No damage to gasket allowing blow by ?

If you are not holding boost on a MBC then we can rule out the ecu as the culprit . So if you got good results with the boost leak test ( less than 1 psi drop per second every 1.5/2 seconds ABOVE 20 psi ) , then the issue may be on the hot side of the turbo .
exhaust leak at manifold usually causes boost creeping...The exhaust doesn't get routed out the wastegate port...overspins turbo in upper rpms aka boost creep
 

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exhaust leak at manifold usually causes boost creeping...The exhaust doesn't get routed out the wastegate port...overspins turbo in upper rpms aka boost creep
I'm confused , or misunderstand what you mean .
Losing exhaust pressure/energy to atmosphere between head and manifold runners , before the scroll area & flapper valve , will cause too much boost to be produced ?

Don't mean to threadjack , lol .
 

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Yeah. Exhaust leak at manifold can cause boost creep.

It's what I always experience with a leak at the head.



Aside from costing me mph at the track it also caused my boost to creep past 6k by a good 3 lbs. Wastegate is physically quieter too...you can tell that the exhaust gas is no longer going through the valve with the same mass flow rate. Some of that exhaust finds its way to the turbine spinning it past what I want. That leak steals some of the control away from the wastegate
 

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Yeah. Exhaust leak at manifold can cause boost creep.

It's what I always experience with a leak at the head.



Aside from costing me mph at the track it also caused my boost to creep past 6k by a good 3 lbs. Wastegate is physically quieter too...you can tell that the exhaust gas is no longer going through the valve with the same mass flow rate. Some of that exhaust finds its way to the turbine spinning it past what I want. That leak steals some of the control away from the wastegate
You will not get more boost with a manifold leak wtf are you talking about
 
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