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boost creep


jeffro

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What causes this?

 

i had my spring backed all the way down to 8psi about 3 weeks ago. recently, it wont go below 9.5, and creeps up till i hit boost cut at 10.5 psi. around 5500 rpm.

 

the wastegate cant be adjust down anymore.

 

what i do know is that im running an open downpipe, whereas before i was running a super restrictive exhaust.

 

is this possibly weather related? or related to the open exhaust? i dont really want to buy an MBC.

 

vacuum leaks, or exhaust leaks before the WG?

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intake manifold. im wondering if the hose isnt cut or something.

 

nope, all vacuum lines look good.

 

i did take the vent nipple off the top of the wg, which opened the opening up by about 4 fold. i thought this was just a vent, but could this unrestricted flow be causing issues?

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What boost controller are you using? I had a shitty manual on my WRX back in the day and it would be all over the place. I went to an electronic never had a problem again. I have a AEM tru-boost on my cobra and they bitch hits and stays at whatever I set it too.
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nope, all vacuum lines look good.

 

i did take the vent nipple off the top of the wg, which opened the opening up by about 4 fold. i thought this was just a vent, but could this unrestricted flow be causing issues?

 

No air should be coming out of that hole except the air being displaced by the diaphragm moving up and down. Try moving your boost reference to the outlet of the turbo, length of hose can have an effect on boost creep and WG response.

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FIAL?

 

no, even more fail. the only thing i changed from my previous setup was my manifold and my downpipe. everything worked fine before.

 

 

i had my vac source hooked up to the turbo outlet before and poor results. then i moved it to the mani and it worked well.

 

my elbow going from my manifold to the wastegate has a crack in it i just noticed. im wondering if that doesnt have anything to do with it.

 

pressure leaking out before the wg/turbo i wouldnt think would give boost creep. if anything, loss of pressure.

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when i went from full exhaust to my open down pipe the boost would skyrocket...

 

thats all the input i have

 

I know Paul and I don't drive Hondas, but I do know that even just adding a downpipe WITH an exhaust on my car can cause boost creep. Paul saw boost creep with an open DP setup, and you are too. Get an exhaust....

 

 

Oh and that wastegate looks craptacular...no offense.

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i've never heard of downpipes and exhaust causing boost creep. Boost creep happens when exhaust gas is unable to bypass the turbine because of the waste gate. Change your waste gate.

 

i read that with the open down pipe, there is zero to little back pressure within the turbine housing. since there is no back pressure, the turbine can over spin because there is nothing limiting how fast the turbine can freely spin. but at the same time how can the turbine spin faster than the pressure of the exhaust.

i think i'm going in the wrong direction here.

 

could the cracked elbow possible create a micro vacuum within the tube, pulling the waste gate towards the closed position?

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No man, turbo's dont want back pressure, the less the better it uses the pressure from the exhaust manifold, that's where you want pressure/velocity.

 

You have a crack between the wastegate and the manifold? That should just cause it to spool slower and possibly build less boost I would assume.

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The times that I've seen a downpipe "cause" boost creep it's because the exhaust without restriction is now the least path of resistance.

 

The point of the wastegate is to divert exhaust gasses from going thru the turbine. What is likely happening here is that the new exhaust has little enough restriction that the path of least resistance has changed from being the wastegate to being out the turbine and thru the exhaust....so now even when the wastegate is open wide, it cannot pull enough of that flow away from the turbine, so the turbo keeps spinning faster and making more boost.

 

So I would say that your new exhaust is too big for the wastegate you have. Possible solutions would be to revise/replace the wastegate so that it can now out-flow the exhaust under all circumstances or place a restriction in the exhaust. I've seen people use metal plates with smaller diameter holes (2.5" small plate put inbetween sections of a 3" pipe for instance) to restrict flow in the exhaust to put things back in balance.

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The times that I've seen a downpipe "cause" boost creep it's because the exhaust without restriction is now the least path of resistance.

 

The point of the wastegate is to divert exhaust gasses from going thru the turbine. What is likely happening here is that the new exhaust has little enough restriction that the path of least resistance has changed from being the wastegate to being out the turbine and thru the exhaust....so now even when the wastegate is open wide, it cannot pull enough of that flow away from the turbine, so the turbo keeps spinning faster and making more boost.

 

So I would say that your new exhaust is too big for the wastegate you have. Possible solutions would be to revise/replace the wastegate so that it can now out-flow the exhaust under all circumstances or place a restriction in the exhaust. I've seen people use metal plates with smaller diameter holes (2.5" small plate put inbetween sections of a 3" pipe for instance) to restrict flow in the exhaust to put things back in balance.

 

ive got a 3" to 2.5" reducer coupler i could clamp on the end. i bet that'd fix it.

 

 

edit, no clamping, blew my last one apart from clamps haha

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ive got a 3" to 2.5" reducer coupler i could clamp on the end. i bet that'd fix it.

 

 

edit, no clamping, blew my last one apart from clamps haha

 

He's speaking on the exhaust side, not intake. He is suggesting that you're dp/exhaust isn't restrictive enough and the exhaust it not flowing through the WG as it should and is causing the boost creep.

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