Dyno graph inside Why is my boost falling off on the big end?
03-02-2017, 01:53 PM
#41
TECH Enthusiast
I think some people on this thread do not understand that your turbo can be making boost, even if your boost gauge is not showing it, because it is not going past the throttle body. If you are referencing the intake manifold for your boost gauge, like you should be for a boost gauge, it will show vacuum at a cruise. Hypothetically just for reference, lets consider a 2500 rpm cruise on the interstate, with a car with no BOV, the BOV is not really a necessary item. You would have no boost on your gauge, showing vacuum, but if you ran a gauge off the compressor housing you would see pressure, this pressurized air residing between the turbo and the throttle body. The purpose of a throttle body is to control air pressure inside the intake manifold. You can also see this same pressure in the intake tract at idle, I do on my setup. It is not a lot of pressure, but it is more than atmospheric. This is why air blows out the BOV. Think of a water tap, when it is opened the pressure in the line is what makes the water run out. The same thing happens with the BOV, it is pressurized behind it, that is why air is blowing out it, but because it is open to the atmosphere, there is not much, because it is being released. Still it is more than atmospheric, it is probably in the range of 101 or 102 kPa if there were a pressure gauge on the compressor housing. It doesn't need to be large, just not be in vacuum, as to mess up the diaphragm on the wastegate. I've never seen a serious race car that wasn't using a line off the compressor housing as the source for opening the wastegate? I have seen setups where the controller sees manifold pressure for control, but the mechanical action of opening the piston comes from the compressor housing.
03-02-2017, 02:55 PM
#43
I think some people on this thread do not understand that your turbo can be making boost, even if your boost gauge is not showing it, because it is not going past the throttle body. If you are referencing the intake manifold for your boost gauge, like you should be for a boost gauge, it will show vacuum at a cruise. Hypothetically just for reference, lets consider a 2500 rpm cruise on the interstate, with a car with no BOV, the BOV is not really a necessary item. You would have no boost on your gauge, showing vacuum, but if you ran a gauge off the compressor housing you would see pressure, this pressurized air residing between the turbo and the throttle body. The purpose of a throttle body is to control air pressure inside the intake manifold. You can also see this same pressure in the intake tract at idle, I do on my setup. It is not a lot of pressure, but it is more than atmospheric. This is why air blows out the BOV. Think of a water tap, when it is opened the pressure in the line is what makes the water run out. The same thing happens with the BOV, it is pressurized behind it, that is why air is blowing out it, but because it is open to the atmosphere, there is not much, because it is being released. Still it is more than atmospheric, it is probably in the range of 101 or 102 kPa if there were a pressure gauge on the compressor housing. It doesn't need to be large, just not be in vacuum, as to mess up the diaphragm on the wastegate. I've never seen a serious race car that wasn't using a line off the compressor housing as the source for opening the wastegate? I have seen setups where the controller sees manifold pressure for control, but the mechanical action of opening the piston comes from the compressor housing.
Edit...it should be even worse on my car cause its a blower which will generate more pressure at idle than the turbo since its RPM dependent.
03-02-2017, 03:21 PM
#44
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.
Yes.... It can... Mine does
Crack the bov and air is leaving the port to atmosphere, Not entering the charge pipe
03-02-2017, 03:28 PM
#45
TECH Enthusiast
I wasn't specifically referring to you ddnspider, your not alone, there are at least 3 people on this thread of that belief. I'm not passive aggressive, but I do believe in speaking in a diplomatic manner, ie I would say I disagreed with a statement, rather than calling someone an idiot. Once again not referring to any specific person here. With the bypass open the pressure will be so small you won't be able to measure it with a boost gauge, it will be very small like 0.1 psi or something like that. Boost gauges typically don't have enough resolution to see that small of a pressure build. If you had something like a barometer that measures small pressure differences, you would see it.
I have a ball bearing turbo, and that may also be part of why I see as much as I do even at an idle. Before I put my turbo on the car I could spin it just by blowing into the turbine housing. Going back to my original statement(see post #22), I'm not saying there is a large amount of boost here at an idle, just that it is not in vacuum, and that it doesn't suck on the piston seal on the wastegate like hooking your wastegate up to the manifold does. There are multiple references to this out there by Tial, JGS and PTE that state this. This is not something I came up with, it is documented by the wastegate manufacturers in their installation instructions etc.
I have a ball bearing turbo, and that may also be part of why I see as much as I do even at an idle. Before I put my turbo on the car I could spin it just by blowing into the turbine housing. Going back to my original statement(see post #22), I'm not saying there is a large amount of boost here at an idle, just that it is not in vacuum, and that it doesn't suck on the piston seal on the wastegate like hooking your wastegate up to the manifold does. There are multiple references to this out there by Tial, JGS and PTE that state this. This is not something I came up with, it is documented by the wastegate manufacturers in their installation instructions etc.
03-02-2017, 03:38 PM
#46
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A ruler, couple zip ties, some aquarium air line, a little water, and you're there. The plastic tubing might even fit on an existing barbed nipple if there's one in your system pre throttle plate.
Last edited by SethU; 03-02-2017 at 03:45 PM.
03-02-2017, 08:00 PM
#50
03-02-2017, 11:14 PM
#51
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.
yes !
Air generally moves because of a pressure difference. the Bypass hangs open and the air comes out- therefore there is higher pressure inside the plumbing than outside it. It might only be 0.1psi higher, but it is higher. To measure this you would probably want a gauge that reads in inches of water above atmospheric- and log it via the computer- the same sort of measurement gauge I use to measure vacuum below atmospheric (in inches of water) in a crank case during boost, to prove the compressor is actually providing PCV action to the crankcase via the compressor inlet if possible.
What is happening as the blades of a fan type device turns? Air molecules, gas molecules, are physical things, just very tiny and transparent to us. The fan blade swings around, through them, pushing them together, gathering them at certain places, perhaps near the tips of the blades or otherwise, creating a pressure difference from one side of the blade to the other thus causing them to move with more purpose in a specific direction and with greater velocity and closer together, as others move in to fill the gaps where previous molecules used to be. Why do new molecules seek to enter the space where previous molecules existed, before those were scooped away? It is entropy, the desire for air molecules to seek the ends of their containers and spread with a speed and distance between them depending on their temperature and pressure, to the full volume of their container.
So yes, the pressure is lower above the blades of your ceiling fan when it is turning a certain direction, and something about airplane wings and lift should also be going through your minds as well, for it is the same sort of magic at work there as well.
Last edited by kingtal0n; 03-02-2017 at 11:45 PM.
03-03-2017, 07:05 AM
#52
So you guys are going to sit here and try to tell me that a turbo, being spun by exhaust, at idle (which is still spinning) wont move enough air to have positive pressure?
Have you seen the size the hole it takes to allow enough air to idle an engine? Its tiny.
Have you ever spun a turbo by hand? it moves enough to feel.
Dont be retards. its def positive pressure. Where you try to measure that is a different story.
Keep you BOV shut, stick a MAP on the charge pipe and idle the car. It will be positive.
Have you seen the size the hole it takes to allow enough air to idle an engine? Its tiny.
Have you ever spun a turbo by hand? it moves enough to feel.
Dont be retards. its def positive pressure. Where you try to measure that is a different story.
Keep you BOV shut, stick a MAP on the charge pipe and idle the car. It will be positive.
03-03-2017, 09:47 AM
#53
I see you are running the eboost controller. I would be willing to bet that your Gate pressure and sensitivity are not set right, causing you boost to go flat up top. Try this, if your goal is let's say 18psi....set the gate pressure to 13psi....and set the sensitivity to 20. Basically keep the gate pressure to around 5 psi less than your target boost pressure.
03-03-2017, 11:34 AM
#57
9 Second Club
03-05-2017, 09:13 AM
#59
This is both an economy feature and performance feature; it is how a factory bypass is generally setup on OEM turbo cars. It allows compressor wheel speed maintenance during throttle lift events, and through them, provides a pressure increase in the space between the compressor inlet and air filter.
If you think of the reverse: imagine you clog the air filter, what happens to the pressure just behind the filter, pre turbo? The pressure will drop in this area, you will have a vacuum when compared to atmosphere. The more you clog/cover the air filter, the lower the pressure will go behind the filter, the fewer air molecules will be available in that space to breath.
03-05-2017, 12:15 PM
#60
So you guys are going to sit here and try to tell me that a turbo, being spun by exhaust, at idle (which is still spinning) wont move enough air to have positive pressure?
Have you seen the size the hole it takes to allow enough air to idle an engine? Its tiny.
Have you ever spun a turbo by hand? it moves enough to feel.
Dont be retards. its def positive pressure. Where you try to measure that is a different story.
Keep you BOV shut, stick a MAP on the charge pipe and idle the car. It will be positive.
Have you seen the size the hole it takes to allow enough air to idle an engine? Its tiny.
Have you ever spun a turbo by hand? it moves enough to feel.
Dont be retards. its def positive pressure. Where you try to measure that is a different story.
Keep you BOV shut, stick a MAP on the charge pipe and idle the car. It will be positive.