Evo 3 16g surging at part throttle !

[v8killer]

Hey guys my Evo 3 16g turbo is surging at part throttle in boost .I'm running speed density and i don't have any boost leaks at the moment. The turbo spools fast so is it just something i'm going to have to live with ?

 

[92AWDHX40]

How are you tuning it.

 

[95gst16g]

It shouldn't...what bov are you running? If you can adjust the spring pressure you may have the bov adjusted to tight.

How are you tuning it.

He said speed density

 

[v8killer]

It shouldn't...what bov are you running? If you can adjust the spring pressure you may have the bov adjusted to tight.


He said speed density

I am running speed density tunning with Jackel. I am runnng a stock bov with the dual port dodge mod ! I have tried using just the top and with both hooked up. I don't see how being too tight would cause it to surge under boost because its supposed to be closed right ?

 

[95gst16g]

Is it under light boost? If its shuttering when you let off it could be too tight but if you have it to the floor then Idk why it would surge

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[v8killer]

another thing is i have it hook to the pressure side of my up pipe not the bov port on the intake. The reason i done this is because at idle it was pulling the bov open causing it to suck in un filtered air. but i have tried almost every way of hooking it up even on a boost/vac port !

Is it under light boost? If its shuttering when you let off it could be too tight but if you have it to the floor then Idk why it would surge

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Yes light boost like when you go to pass someone !

 

[95gst16g]

Sounds like the bov may be tour problem...just try a stock 1 g bov and see what happens

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[v8killer]

Sounds like the bov may be tour problem...just try a stock 1 g bov and see what happens

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The bov seam to work normal ? it held 25+lbs of boost and opens good !

 

[95gst16g]

But if the spring is stiff it will work when you are in high boost but say you hit like 5psi and let off it will cause compresser surge if there is too much tension on the spring.

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[ramsack]

BOV flutter is not surge.

 

[JusMX141]

BOV flutter is not surge.

....if the noise you're hearing is coming from the valve itself and not the turbo.

If the valve is not opening and the flutter sound is coming from the turbo, it's absolutely compressor surge.

 

[ramsack]

Then it's not BOV flutter...

 

[95gst16g]

Yeah well if it isn't opening at all where does all of the extra air go when you let off? I would think it would cause the air to cause a little disruption from the compressor? I'm just thinking the bov isn't opening at all with the lower boost levels...Idk I'm no expert.

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[ramsack]

I guess a BOV is going to make the exact same sound at 1 psi as it does at 20 psi so how are you positive it's not opening. No one who ever claims any of this has ever hooked a boost gauge up to their charge pipes to see what is going on, or even tried to witness first hand to actually watch if their BOV opens or not. Pressure acts everywhere with equal force, so I'd like to know how a turbo's shaft is going to slam into its bearing from a pressure spike, especially with these little part-throttle flutters.

 

[95gst16g]

Yeah I was just suggesting to maybe try a stock bov and see if it goes away then you will know for sure what's causing the noise

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[brian9397gsx]

With a 1g bov modded you loose the quick release part of the valve making it more likley to have light comp surge at part throttle or light boost

 

[v8killer]

Guys it is the turbo making the noise and not the valve i can tell the difference, also i noticed today the the boost will flutter also when it does this ! yes the valve is tight when hooked up to the positive side because you don't have the vac on the port to help pull it open when the throttle is closed so that may be my problem. I may try a boost/vac source again !

 

[brian9397gsx]

Where are you sourcing your vacuum line for your bov?

 

[ramsack]

You definitely need a source that is vacuum when there is no boost present (intake manifold) to help snap the BOV open during partial throttle boosts. There is no magical tradeoff to have a sprung BOV open at low boost but also keep shut high boost. Most with a diaphragm will somewhat alleviate the problem, but they rely on springs too. The best kind to use are the kind that rely on surface area on the charge pipe side versus larger area on the vac/boost line side.

 

[v8killer]

Where are you sourcing your vacuum line for your bov?

on the uicp boost source !

 

[ramsack]

Switch it over to somewhere on the intake manifold, and NOT teed into a line that goes to the FPR or a boost gauge. It needs its own vacuum source right off the manifold, and it's recommended to use some line with decent inner diameter, like 3/16". I doubt your BOV is even opening at all.

 

[v8killer]

Switch it over to somewhere on the intake manifold, and NOT teed into a line that goes to the FPR or a boost gauge. It needs its own vacuum source right off the manifold, and it's recommended to use some line with decent inner diameter, like 3/16". I doubt your BOV is even opening at all.

It's opening. When you back off the throttle you can hear it good !

 

[ramsack]

Yes, it will open at high boost, and will cause this "surge" at a decently high boost level too because of not having vacuum to keep it open. The only thing to open it now is boost versus less boost. A properly working BOV operates by seeing boost versus vacuum, and the vacuum stays vacuum, which holds the BOV open until boost is almost non-existent.

 

[v8killer]

Yes, it will open at high boost, and will cause this "surge" at a decently high boost level too because of not having vacuum to keep it open. The only thing to open it now is boost versus less boost. A properly working BOV operates by seeing boost versus vacuum, and the vacuum stays vacuum, which holds the BOV open until boost is almost non-existent.

You have to remember my stock bov has been modifed to a dual port one above and below the diaphram. when i had it hooked up the the manifold at vac on just the top port it would hang the valve open at idle causing a vac leak. when i would tee into both ports from the manifold it would stay shut but it would leak under a boost leak test pretty low ? So there is my problem.

 

[ramsack]

You're running speed density, it doesn't matter if it the BOV is open or not. A vacuum leak will be present no matter what as the charge pipes are basically at atmospheric pressure at idle, anyway. It's normal for a BOV to be open during idle, even without this mod, which is the main reason cars die when they are vent the BOV when running with a stock MAF. I read the article on that dodge mod once and I played out different situations in my head to try to understand it, and it seemed like complete crap to me. Trying to get a BOV that has equal surface areas on both sides of the diaphragm chambers is like polishing a turd. Sprung BOVs are used because they are simple and they are cheap. I'd suggest finding one that operates completely on pressure differential (HKS SSQV, Synapse, Toyota MR2 mk2, some Saabs I believe).