Wastegates...Please Explain ??
#1
08-24-2008, 03:44 AM
Join Date: Aug 2008
Location: East Yorkshire, UK
Posts: 32
Rep Power: 18 
Wastegates...Please Explain ??
Hi Guys, Firstly I'd like to congratulate everyone on such an informative forum, and secondly I hope someone can explain the exact operation of the wastegate actuators. As I understand, on a standard K16 car the wastegates are set to open at around .7-.8 bar, when this pressure operates against the springs allowing gas to escape through the hot exhaust side and slowing the turbine. However, since an FVD reflash my car now shows .9-1.0 bar so I guess there must be some kind of electronic control somewhere. So my questions are: Why aren't my wastegates opening to allow the excess pressure out ? and if they can be controlled electronucally why do so many people used upgraded wastegate springs? Apologies if this has been answered before, but I can't find anything or get a satisfactory answer anywhere else.
#2
08-24-2008, 07:43 AM
long story short...
the wastegates control the boost.. and they are controlled electronicly by a electronic boost controller (porsche calls it a frequency valve) there is a vacuum hose attached to the y pipe that is attached to the boost controller then is's t'd off to the wastegates(if you look at your wastegates u can see there is a vacuum line attached to them) ... so when the engine is under boost the computer opens and shuts the frequency valve which allows pressure to open and close the wastegates in turn controlling the boost by allowing exhaust gas to bypass the turbos.
some people put larger springs or add more spring pre-load to there exisiting wastegate accuators to hold the wastegate shut allowing the turbo to make more boost this is only good to the efficency point of the turbo.... it that case you not able to let enough exhaust gas out and you begin to lose boost at higher rpms
hope this helps
tim
the wastegates control the boost.. and they are controlled electronicly by a electronic boost controller (porsche calls it a frequency valve) there is a vacuum hose attached to the y pipe that is attached to the boost controller then is's t'd off to the wastegates(if you look at your wastegates u can see there is a vacuum line attached to them) ... so when the engine is under boost the computer opens and shuts the frequency valve which allows pressure to open and close the wastegates in turn controlling the boost by allowing exhaust gas to bypass the turbos.
some people put larger springs or add more spring pre-load to there exisiting wastegate accuators to hold the wastegate shut allowing the turbo to make more boost this is only good to the efficency point of the turbo.... it that case you not able to let enough exhaust gas out and you begin to lose boost at higher rpms
hope this helps
tim
#3
08-24-2008, 08:38 AM
Join Date: Aug 2008
Location: East Yorkshire, UK
Posts: 32
Rep Power: 18
Thanx Tim,
Clear as mud now, no only joking, if I understand correctly then, by reflashing the computer this will alter the parameters of the frequency valve? In your opinion should I fit upgraded wastegate actuators (such as the ones sold by Evoms) to a pair of K16/24s I am thinking of replacing my 16s with ?
Cheers...
Clear as mud now, no only joking, if I understand correctly then, by reflashing the computer this will alter the parameters of the frequency valve? In your opinion should I fit upgraded wastegate actuators (such as the ones sold by Evoms) to a pair of K16/24s I am thinking of replacing my 16s with ?
Cheers...
#4
08-24-2008, 09:08 AM
1. It is Pressure, not vacuum that is sent to the WG.
2, The springs RESIST opening under boost preesure. The computer will actively open the wastegate when needed. However, under high boost pressure the springs are inadeuate to hold the WG closed. Hence the need for upgraded springs.
Programming cannot overcome wimpy springs.
A
2, The springs RESIST opening under boost preesure. The computer will actively open the wastegate when needed. However, under high boost pressure the springs are inadeuate to hold the WG closed. Hence the need for upgraded springs.
Programming cannot overcome wimpy springs.
A
#5
08-24-2008, 09:40 AM
Thanx Tim,
Clear as mud now, no only joking, if I understand correctly then, by reflashing the computer this will alter the parameters of the frequency valve? In your opinion should I fit upgraded wastegate actuators (such as the ones sold by Evoms) to a pair of K16/24s I am thinking of replacing my 16s with ?
Cheers...
Clear as mud now, no only joking, if I understand correctly then, by reflashing the computer this will alter the parameters of the frequency valve? In your opinion should I fit upgraded wastegate actuators (such as the ones sold by Evoms) to a pair of K16/24s I am thinking of replacing my 16s with ?
Cheers...
#6
08-24-2008, 09:43 AM
Join Date: Aug 2008
Location: East Yorkshire, UK
Posts: 32
Rep Power: 18
So, let me try to understand again, if the computer actively opens the wastegates by applying pressure to the springs via the pressure lines when required, in my case at around .9-1.0 bar then what is the point of upgraded springs as full boost pressure has already been reached in order pressure the lines and activate the wastegates...Apologies for any stupidity...please be gentle.
#7
08-24-2008, 10:01 AM
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The other thing waste gates are for is when you blow off the pedal. The is a delay between when you shut it down. The turbos are still blowing. I believe when you let off
the vacuum opens the waste gates to allow the over pressure out at that time.
the vacuum opens the waste gates to allow the over pressure out at that time.
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#8
08-24-2008, 10:01 AM
Correct pressure activates the wastegates and progammimg cannot compensate for wimpy springs.... I use the term vacuum hose to represent the rubber hose that connects every thing together 
1. It is Pressure, not vacuum that is sent to the WG.
2, The springs RESIST opening under boost preesure. The computer will actively open the wastegate when needed. However, under high boost pressure the springs are inadeuate to hold the WG closed. Hence the need for upgraded springs.
Programming cannot overcome wimpy springs.
A
2, The springs RESIST opening under boost preesure. The computer will actively open the wastegate when needed. However, under high boost pressure the springs are inadeuate to hold the WG closed. Hence the need for upgraded springs.
Programming cannot overcome wimpy springs.
A
#9
08-24-2008, 10:09 AM
Join Date: Aug 2008
Location: East Yorkshire, UK
Posts: 32
Rep Power: 18
#10
08-24-2008, 10:09 AM
The whole thing is a mechanical system being controlled by an electronic system. It's the interplay between the two (especially when you change the parameters it was designed for) that gets interesting.
Ok, here's my best understanding and I'd welcome being corrected if I've got this wrong.
The ecu is connected to the boost frequency solenoid (N75 valve) and it electronically signals it to open and close. When open, it allows manifold pressure to run to the wastegate actuators. When closed, it does not. You can actually log the signal frequency with a durametric.
Now, when the valve is open it exerts pressure on the spring and diaphragm inside the wastegate actuator, pressing the wastegate actuator rod down which mechanically opens a flapper valve inside the turbine housing and lets hot exhaust gas circumvent the turbine wheels (thereby slowing the compressor wheel and reducing boost).
Programming can clearly tell the N75 valve to open less frequently, tricking the wastegates into staying shut longer, thus producing more boost.
However, if you think about it from the turbine side, you've now got a mechanical flapper valve connected to a rod that is only being held in the up (i.e. flapper closed) position because a spring is holding it there. That spring was only designed to hold that flapper shut up until .7 or so bar. The exhaust gas pushing through the turbine housing at 1.2 bar is physically overcoming the spring inside the actuator housing and forcing it open, no matter what the ECU and N75 valve are trying to do on the other end of the spring. Now, eventually the ECU will compensate with its N75 signal and you'll hit the desired boost, but there's been time lost mucking about trying to compensate.
A stronger spring lets the flapper stay closed and eliminates the N75 "seeking" trying to set the right boost level.
It's a balancing act. If the spring is too strong, the flapper doesn't open when you want it to and you run into an overboost situation pretty quick.
Any clearer?
Ok, here's my best understanding and I'd welcome being corrected if I've got this wrong.
The ecu is connected to the boost frequency solenoid (N75 valve) and it electronically signals it to open and close. When open, it allows manifold pressure to run to the wastegate actuators. When closed, it does not. You can actually log the signal frequency with a durametric.
Now, when the valve is open it exerts pressure on the spring and diaphragm inside the wastegate actuator, pressing the wastegate actuator rod down which mechanically opens a flapper valve inside the turbine housing and lets hot exhaust gas circumvent the turbine wheels (thereby slowing the compressor wheel and reducing boost).
Programming can clearly tell the N75 valve to open less frequently, tricking the wastegates into staying shut longer, thus producing more boost.
However, if you think about it from the turbine side, you've now got a mechanical flapper valve connected to a rod that is only being held in the up (i.e. flapper closed) position because a spring is holding it there. That spring was only designed to hold that flapper shut up until .7 or so bar. The exhaust gas pushing through the turbine housing at 1.2 bar is physically overcoming the spring inside the actuator housing and forcing it open, no matter what the ECU and N75 valve are trying to do on the other end of the spring. Now, eventually the ECU will compensate with its N75 signal and you'll hit the desired boost, but there's been time lost mucking about trying to compensate.
A stronger spring lets the flapper stay closed and eliminates the N75 "seeking" trying to set the right boost level.
It's a balancing act. If the spring is too strong, the flapper doesn't open when you want it to and you run into an overboost situation pretty quick.
Any clearer?
Last edited by Seal Grey Matte; 08-24-2008 at 10:40 AM.
#12
08-24-2008, 10:12 AM
100% correct
Thanx Tim,
Clear as mud now, no only joking, if I understand correctly then, by reflashing the computer this will alter the parameters of the frequency valve? In your opinion should I fit upgraded wastegate actuators (such as the ones sold by Evoms) to a pair of K16/24s I am thinking of replacing my 16s with ?
Cheers...
Clear as mud now, no only joking, if I understand correctly then, by reflashing the computer this will alter the parameters of the frequency valve? In your opinion should I fit upgraded wastegate actuators (such as the ones sold by Evoms) to a pair of K16/24s I am thinking of replacing my 16s with ?
Cheers...
#13
08-24-2008, 10:46 AM
Join Date: Aug 2008
Location: East Yorkshire, UK
Posts: 32
Rep Power: 18 The whole thing is a mechanical system being controlled by an electronic system. It's the interplay between the two (especially when you change the parameters it was designed for) that gets interesting.
Ok, here's my best understanding and I'd welcome being corrected if I've got this wrong.
The ecu is connected to the boost frequency solenoid (N75 valve) and it electronically signals it to open and close. When open, it allows manifold pressure to run to the wastegate actuators. When closed, it does not. You can actually log the signal frequency with a durametric.
Now, when the valve is open it exerts pressure on the spring and diaphragm inside the wastegate actuator, pressing the wastegate actuator rod down which mechanically opens a flapper valve inside the turbine housing and lets hot exhaust gas circumvent the turbine wheels (thereby slowing the compressor wheel and reducing boost).
Programming can clearly tell the N75 valve to open less frequently, tricking the wastegates into staying shut longer, thus producing more boost.
However, if you think about it from the turbine side, you've now got a mechanical flapper valve connected to a rod that is only being held in the up (i.e. flapper closed) position because a spring is holding it there. That spring was only designed to hold that flapper shut up until .7 or so bar. The exhaust gas pushing through the turbine housing at 1.2 bar is physically overcoming the spring inside the actuator housing and forcing it open, no matter what the ECU and N75 valve are trying to do on the other hand. Now, eventually the ECU will compensate with its N75 signal and you'll hit the desired boost, but there's been time lost mucking about trying to compensate.
A stronger spring lets the flapper stay closed and eliminates the N75 "seeking" trying to set the right boost level.
It's a balancing act. If the spring is too strong, the flapper doesn't open when you want it to and you run into an overboost situation pretty quick.
Any clearer?
Ok, here's my best understanding and I'd welcome being corrected if I've got this wrong.
The ecu is connected to the boost frequency solenoid (N75 valve) and it electronically signals it to open and close. When open, it allows manifold pressure to run to the wastegate actuators. When closed, it does not. You can actually log the signal frequency with a durametric.
Now, when the valve is open it exerts pressure on the spring and diaphragm inside the wastegate actuator, pressing the wastegate actuator rod down which mechanically opens a flapper valve inside the turbine housing and lets hot exhaust gas circumvent the turbine wheels (thereby slowing the compressor wheel and reducing boost).
Programming can clearly tell the N75 valve to open less frequently, tricking the wastegates into staying shut longer, thus producing more boost.
However, if you think about it from the turbine side, you've now got a mechanical flapper valve connected to a rod that is only being held in the up (i.e. flapper closed) position because a spring is holding it there. That spring was only designed to hold that flapper shut up until .7 or so bar. The exhaust gas pushing through the turbine housing at 1.2 bar is physically overcoming the spring inside the actuator housing and forcing it open, no matter what the ECU and N75 valve are trying to do on the other hand. Now, eventually the ECU will compensate with its N75 signal and you'll hit the desired boost, but there's been time lost mucking about trying to compensate.
A stronger spring lets the flapper stay closed and eliminates the N75 "seeking" trying to set the right boost level.
It's a balancing act. If the spring is too strong, the flapper doesn't open when you want it to and you run into an overboost situation pretty quick.
Any clearer?
#14
08-24-2008, 01:00 PM
Join Date: Aug 2008
Location: East Yorkshire, UK
Posts: 32
Rep Power: 18 The wastegate actuator has a spring in it that has a tension on it. Every spring has a certain amount of tension. let's say, for arguments sake, that your wastegate has a spring with 10lbs. of tension. That means the wastegate will open at 10 lbs. of boost. Now the wastegate actuator has a nipple on top of it with a vacuum hose on it, that vacuum hose gets routed to the intsake manifold. When you are driving your car under boost your intake manifold becomes pressurized, when you are running around without boost your intake manifold sees a vacuum (vacuum is created by the normal operation of your engine). When your intake manifold sees pressure it puts pressure into all the vacuum hoses that are attached to it including the one going to your wastegate. when the hose going to your wastegate has 10 psi in it the air pushes th spring which further moves the rod that will open the flapper in your turbine housing and then the exhaust ga bypasses the turbine wheel, preventing it from spinning faster and then your boost is controlled at 10psi. When you add an electronic boost control you bleed off air pressure from that wastegate hose. In other words, if you want to run 15lbs. of boost you need to bleed off five pounds of boost before the wastegate. It does this electronically through a solenoid. By bleeding off 5 lbs. of air the wastegate will still open at a 10lbs. air signal to the spring but the car is really running 15lbs. of boost but the wastegate does not know that. There is a limit to what the factory watgate can control the boost up to because of many parameters but this is the basic way a wastegat and boost controller controls boost.
#15
08-24-2008, 01:39 PM
So I think what you're saying is that the internal pressure of the hot (exhaust/turbine) side of the turbo can affect the operation of the wastegate valve causing it to open prematurely. Would this not happen regardless of boost pressure (generated by compressor) as there is nothing to regulate the pressure generated by exhaust gases that turn the turbine except the wastegates which we now understand are controlled by the boost frequency valve ?