Dyno graph inside Why is my boost falling off on the big end?
Staging Lane
Joined: Sep 2012
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Am I wrong in thinking that even if you put the reference for the wastegate in the compressor housing its still going to see vacuum? Turbos do not create positive pressure at idle or even in light load situations, wouldn't this mean it is seeing vacuum at that time? Plus Isn't whole point of running the reference from the manifold to control the level of boost the engine is actually seeing? Pressure is lost through the IC and piping.
This at least was my understanding. Let me know if I am wrong. lol
This at least was my understanding. Let me know if I am wrong. lol
TECH Enthusiast
Joined: Jan 2012
Posts: 557
Likes: 9
From: Bowling Green KY
Am I wrong in thinking that even if you put the reference for the wastegate in the compressor housing its still going to see vacuum? Turbos do not create positive pressure at idle or even in light load situations, wouldn't this mean it is seeing vacuum at that time? Plus Isn't whole point of running the reference from the manifold to control the level of boost the engine is actually seeing? Pressure is lost through the IC and piping.
This at least was my understanding. Let me know if I am wrong. lol
This at least was my understanding. Let me know if I am wrong. lol
TECH Enthusiast
Joined: Jan 2012
Posts: 557
Likes: 9
From: Bowling Green KY
One more question , I'm still getting light smoke after installing a Mighty Mouse ls Wild setup, and all new -10 an drains with a turbo werx exa pump and brand spanking new turbo ! This is the most frustrating thing as I battled this problem all last fall and still can't seem to figure it out . I've read some people clock their turbo an inch forward or clockwise? I really don't understand why I'm still getting smoke when I let off, or come to a stop . All new valve stem seals, the right pcv setup, a proper drain. Could my turbo possibly need a restrictor? This is the most frustrating issue I've had since switching over to turbo! I see 65-70 psi oil pressure at wot . But it never smokes under boost , it's always when I back off or at low Rpms . Could there be excessive blow by in the motor causing it ? That doesn't make sense though considering it doesn't ever do it under wot and only when I'm babying the car ...
8 psi spring as stated above also
8 psi spring as stated above also
Originally Posted by ScottyBG
The lowest the pressure we should see at the compressor housing should be atmospheric. Even at an idle my turbo generates pressure in the intake pipe, I know this because my BOV is open and air is blowing out it. The compressor housing is where you want to get your boost line from for your wastegate, not the manifold. The only place there is any appreciable amount of vacuum is behind the throttle blade in the intake.
Thread Starter
TECH Apprentice
Joined: Aug 2015
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According to Turbonetics' literature, you should not need to run a restrictor on that turbo. It does come with a fitting on the oil inlet, with a screen on it correct? I believe this fitting lets the correct amount of oil in. Is it possible it is just a rich fueling condition creating the smoke? I do not run a restrictor on my 7875, and never noticed any smoke.
TECH Enthusiast
Joined: Jan 2012
Posts: 557
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From: Bowling Green KY
When I put paper, or thread in front of my BOV at idle, it blows it pretty good, if there were not more pressure in the tube than atmospheric it would not blow out it. The turbo is spinning, and the throttle blade is closed, there is no where for the air to go, other than out the bov. I've no doubt the intake piping is slightly pressurized. Its not much, certainly less than 1 psi, but it is more than atmospheric.
TECH Enthusiast
Joined: Jan 2012
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From: Bowling Green KY
If the intake pipe were not pressurized we would need to put air filters over our BOV's so the engine would not suck dirt in them when they are open. Because the pipe is pressurized we don't need to. Think, that turbo is spinning, when it is spinning it pushes air. I agree that it is not much at an idle, but with a closed throttle blade, pretty much any at all will make a small positive pressure. A fan can't spin without moving some air and it moves this air by creating a higher pressure in front of the blades. Air flows from high pressure to low pressure.
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Verdad Gallardo TECH Enthusiast
Joined: Jan 2012
Posts: 557
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From: Bowling Green KY
Here is some interesting reading, this has been beaten to death on the interwebs.
There are various links from this thread that cover the topic regarding a waste gate and why we never hook it up to a manifold vacuum source.
https://www.theturboforums.com/threa...no-b-c.330186/
There are various links from this thread that cover the topic regarding a waste gate and why we never hook it up to a manifold vacuum source.
https://www.theturboforums.com/threa...no-b-c.330186/
There is no way to isolate the gate function from exhaust gas pressure. The exhaust pressure is always opposing the valve face
The only way to keep steady boost is to have closed loop controller that will add reference vs rpm
And whether your turbo is creating a high pressure or low pressure in the charge pipe at idle vs the absolute pressure around it is all based on engine consumption vs turbo output.
I have a 94mm gt55 and when the hotside and turbo is all at temp it will have a very slight pre TB charge pressure at idle. When it's cold it is negative
The only way to keep steady boost is to have closed loop controller that will add reference vs rpm
And whether your turbo is creating a high pressure or low pressure in the charge pipe at idle vs the absolute pressure around it is all based on engine consumption vs turbo output.
I have a 94mm gt55 and when the hotside and turbo is all at temp it will have a very slight pre TB charge pressure at idle. When it's cold it is negative
9 Second Club
Joined: Nov 2003
Posts: 13,616
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From: Norn Iron
The plumbing config you are using would offer you the lowest range of boost control options and if EGBP is high, then total possible boost will be even lower.
Again...Read the instructions.
The reason your bov is open is because the pressure inside the charge pipes is greater than what the manifold is seeing with a closed throttle body.
And like rotary said, those turbines are known to hit a wall around 5500 rpm. No matter how you control boost you won't be able to get the power to carry much further if at all.
And like rotary said, those turbines are known to hit a wall around 5500 rpm. No matter how you control boost you won't be able to get the power to carry much further if at all.
Holy derp! LOL at making positive pressure at idle. The turbo is spinning but you have this giant blockage called a throttlebody at idle that only has a small opening in it. You are moving air not making positive pressure.
Is there positive pressure vs absolute pressure pre TB? Yes can be... So are u the durp?
positive pressure in my terms is anything greater than atmospheric, i.e. more than 0psi. And nobody Makin any power I see referencea a waste gate or controller at the turbo, your motor isn't seeing the same pressure as at the compressor due to losses in the intake tract like the fmic.
9 Second Club
Joined: Nov 2003
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From: Norn Iron
positive pressure in my terms is anything greater than atmospheric, i.e. more than 0psi. And nobody Makin any power I see referencea a waste gate or controller at the turbo, your motor isn't seeing the same pressure as at the compressor due to losses in the intake tract like the fmic.
0psi would be absolute vacuum.
And if you have such huge losses through the intake tract or IC...fix your ****.
now put what you wrote in terms of a boost gauge. I'm not talking about vacuum, I'm talking about atmospheric pressure or the transition point between boost and vacuum like on a gauge. We can talk semantics in wording but the intake tract still isn't generating positive pressure above atmospheric pressure at idle with a BOV sitting open.
OP nice numbers.
Regarding the WG source, I can see where running this off of the compressor would give the quickest response signal to the WG, and letting it see vacuum is not good for the diaphragm...but...question; I've always thought running WG signal to right before the TB would account for any loss through the intercooler and piping and the boost should remain stable. Is this incorrect? Wouldn't the losses/differences between the compressor and TB increase with RPM/boost/etc?
Regarding the WG source, I can see where running this off of the compressor would give the quickest response signal to the WG, and letting it see vacuum is not good for the diaphragm...but...question; I've always thought running WG signal to right before the TB would account for any loss through the intercooler and piping and the boost should remain stable. Is this incorrect? Wouldn't the losses/differences between the compressor and TB increase with RPM/boost/etc?