wastegating facts

sheesh man, lighten up. maybe a little help here helping us understand your "turbocharger law" you are talking about. Most here have a lot of real world experience that far outweighs what one can learn in a book. If you are purely speaking about pressure as in lbs per square inch in the entire exhaust system pre turbo such as TIP(Turbine inlet pressure) then I and many others have actually measured said exhaust pressure that contradicts what you are telling us.

If you want to remain silent with your explanation I understand, we are just simpletons in you fish pond
 
JWT said:
I hope that reading this will inspire some of you to read a book on turbochargers, I feel that no matter how much I try to explain turbocharging facts some of you will still not believe what I am saying, I can appreciate that you don’t know who I am so why should you. But I will repeat again the exhaust must produce sufficient horse power to meet the compressor demand, a turbocharger is a turbine driven supercharger.
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Your assuming that when the wastegate opens that the shaft speed will stay the same. Did you read just one book on turbocharging? Maybe it was flawed. Your basically saying that you take away one half of the driving force on a divided housing, and the turbine pressure increases. I agree that the exhaust must create sufficient HP to drive the compressor. You just don't miraculously gain more turbine pressure by bypassing the turbine. You should fill out your signature. Maybe your Pius Bell or someone. Lead product Engineer for Borg?
 
What about non wastegated turbos ! Some of you with this knowledge explain this to me . How does that work ? I run a GT4094 non waste gated turbo. Where does the exhaust gas go . Does it just blow through at a certain point on the map. I didnt stay at the Holliday in Express last night.
 
C.A.P. You are correct. there is a sweet spot on the turbine map at which point the pressure drops to a very small amount and you need a wastegate to open to bring the pressure back up again to drive the compressor :umno::bang:poke::pop:
 
As you all know the turbine is driven by the positive pumping pressure of the cylinders and the compressor is attached to the turbine by a shaft.
you also must know that if the compressor wheel pressure is a result of compressor speed the air is drawn in through the inducer and thrown out of the exducer at a high velocity; this air is converted by slowing down to static pressure before entering the engine.
When the turbo is designed the compressor and housing map is chosen to meet the engine requirements, a turbine housing is then matched to give the best possible performance; the turbine housing A/R ratios can be chosen for various response and because a smaller A/R ratio will not perform well at higher exhaust flows if a low end response is required a wastegated housing is sometimes chosen.
the problem with a wastegated housing is it will only supply a balanced exhaust driving pressure until the wastegate is opened and some of that balanced exhaust energy is diverted around the turbine to control boost pressure this will happen during acceleration and is controlled by compressor boost pressure not wheel speed.
as the engine accelerates engine speed is increasing and air demand continues to rise so wheel speed and flow must also increase (you can see this on your compressor map look at pressure ratios and speed lines) more flow and speed more compressor horse power demand but the problem is the compressor is still opening the wastegate to control pressure so the turbine pressure must increase to supply that demand, the result is higher exhaust pressure than compressor pressure.
 
JWT said:
As you all know the turbine is driven by the positive pumping pressure of the cylinders and the compressor is attached to the turbine by a shaft.
you also must know that if the compressor wheel pressure is a result of compressor speed the air is drawn in through the inducer and thrown out of the exducer at a high velocity; this air is converted by slowing down to static pressure before entering the engine.
When the turbo is designed the compressor and housing map is chosen to meet the engine requirements, a turbine housing is then matched to give the best possible performance; the turbine housing A/R ratios can be chosen for various response and because a smaller A/R ratio will not perform well at higher exhaust flows if a low end response is required a wastegated housing is sometimes chosen.
the problem with a wastegated housing is it will only supply a balanced exhaust driving pressure until the wastegate is opened and some of that balanced exhaust energy is diverted around the turbine to control boost pressure this will happen during acceleration and is controlled by compressor boost pressure not wheel speed.
as the engine accelerates engine speed is increasing and air demand continues to rise so wheel speed and flow must also increase (you can see this on your compressor map look at pressure ratios and speed lines) more flow and speed more compressor horse power demand but the problem is the compressor is still opening the wastegate to control pressure so the turbine pressure must increase to supply that demand, the result is higher exhaust pressure than compressor pressure.
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How can turbine pressure increase when you are allowing pressure to be vented through the wastegate. This is like saying a pump blows a hole in the casting and you build more pressure with the hole in it. This would be fantastic, if it were true. You are making assumptions that I believe are incorrect. Your assuming that when the wastegate opens that no turbine speed is lost. Perhaps when the wastegate is opened the engine is allowed to breathe better so you now have decreased the load on the compressor and maybe that is what is allowing the shaft to maintain rpm.
 
Looking at what he is saying in the first post is technically correct but perhaps not as clearly explained on paper.

Think about it this way - can you build more boost pressure that the wastegate is set for? For example if the wastegate is set at 40 lbs can you still achieve 50 lbs of boost? If you can, then you must still have some turbine drive pressure. If the gate bleeds off three cylinders then the remaining ones are seeing a higher pressure.

It seems to me he is taking a lot or words to try and describe high drive pressure greater that 1:1. Guys have been measuring this for a long time. If greater than 1:1 then yes, turbine pressure is increased.

He is also assuming that the truck is still accelerating which would require more boost and turbine pressure to maintain acceleration. If no acceleration then static condition occurs and pressures reach new equilibrium (hey, I used a big word too).

Just my thoughts.

Paul
 
Lets simplify this discussion and pretend that we are talking about an open throat housing where the wastegate bypasses pressure from all cylinders. When the wastegate opens? Explain from here.
 
This would work the same as turbo with wastegates on both ports the pressure driving the wheel would have to increase, you have to remember that a turbocharger is driven by exhaust pressure; and as I said before diverting some of exhaust gasses reduces driving HP so the pressure driving the wheel has to increase as engine demand increases; flow is load more flow needs more driving pressure

If you were driving a wheel attached to a rotating air pump with two water hoses and you started to shut one of the hoses down do you think the pump wouldn’t slow down? You would have to increase the pressure on the other hose to maintain the same driving force and increase it even more if you need to pump more air.
 
So...a turbo that only wastegates off one half of the turbine housing is bad.
point taken...is there anything else you are trying to educate us laymen?
 
This post basically says, when you are setup to run X psi of max boost, once the wastegate opens some of the driving force is bypassing the turbine, so in order to maintain your X psi of boost the turbine needs more pressure. At this point if the X amount of boost starts to fall the wastegate starts to close and return the turbine pressure. Seems obvious. Or am I missing the point of this thread?
 
After re-reading the original post, how would the wastegate fully open and close at one pre-set psi value? Electronic gate?
 
Maybe this guy is trying to say that if Boost output is maintained and wastegate opens, and boost is still maintained, drive pressure must remain constant. Not increase but remain constant.

If it takes 10 lbs of exhaust to spin 5 lbs of boost and the wastegate suddenly opens and bypasses 4lbs of exhaust, I think JWT means that if boost is going to stay at 5 lbs, there must now be 14 lbs of exhaust coming out of the engine, but only 10 lbs measurable on a turbine inlet pressure gauge because 4 lbs are being bled off. You are losing everyone by saying that pressure will increase. Pressure will not increase, total flow will increase if boost is to be maintained.

JWT, your wording is throwing everyone off. Here is how I interpret your wording. I'm driving down the road in a V8 gasser. I pull two plug wires while I'm going 60 MPH. I maintain speed by pressing the accelerator down more. The other 6 cylinders have to up their HP output to maintain speed BUT HP WAS NOT INCREASED. Your statement: wastegate opens, pressure must increase delta niner! Exhaust flow must increase but pressure will not and cannot increase with an open wastegate. Thats as ridiculous as you saying hey dude, my tire is a little low, why don't you slash it so pressure will increase. DA

JWT, thanks for teaching everyone nothing. No crap if you open the wastegate a bypass exhaust boost will fall. No crap the shaft will lose speed.

I'll bet with high tech equipment, you would actually see that the wastegate flutters a bit, constantly changing exhaust pressure according to boost pressure pushing on the actuator.
 
JWT said:
This would work the same as turbo with wastegates on both ports the pressure driving the wheel would have to increase, you have to remember that a turbocharger is driven by exhaust pressure; and as I said before diverting some of exhaust gasses reduces driving HP so the pressure driving the wheel has to increase as engine demand increases; flow is load more flow needs more driving pressure

If you were driving a wheel attached to a rotating air pump with two water hoses and you started to shut one of the hoses down do you think the pump wouldn’t slow down? You would have to increase the pressure on the other hose to maintain the same driving force and increase it even more if you need to pump more air.
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This is correct, but as I said before you are assuming the turbo will maintain the same speed. The idea of a wastegate to to keep from overspeeding the turbo! You are making in accurate assumptions. To move a shaft given speed it will require x force, this point is taken, but opening a wastegate will relieve drive pressure which will help to drop your boost pressure. Remember boost is a restriction, so now that you have dropped your restriction, the compressor wheel will not require as much force to be spinning at given rpm.

Bottom line two hoses hooked up to the same pump, with seperate valves half open, assume you at this point you are running rated flow and pressure from the pump. Now open one valve all the way and tell me that the pump pressure will not fall.
 
I looked at a few of my runs on my logger this is a thumper tnetics 102mm with a 60mm gate on a small chevy. tps 100% boost 42psi gate set at 45psi 8000rpm drive pressure 38psi. tps 100% boost 45psi 8400rpm drive pressure 43psi. tps 100% boost 46psi 8600rpm w/g open drive pressure 30psi. That tell me that if your drive pressure is increasing with the gate open maybe you need a bigger gate? I run an external on my 12v also just because they are higher flowing
 
I do have a question for anybody...i have a stock charger blocked wastegate and can push close to 45 but can bark it pretty good...i can bark at less than 35psi...just got an elbow and wondering putting that in and gated at 35 will that help my bark at all? How if it does?
 
You must take the pressure reading from both ports to get the true reading.

This is what an engineer from BorgWarner Dave Andrews who has also worked for Garrett said regarding this question.
He has worked on high pressure applications and durability testing.

The question was; when wastegate valve begins to open, what happens to exhaust manifold pressure?

His answer; Exhaust manifold pressure always goes up, since flow is being diverted around the turbine wheel, the expansion ratio across the wheel essentially exhaust manifold pressure must increase to create the same power for the compressor.
 
JWT said:
His answer; Exhaust manifold pressure always goes up, since flow is being diverted around the turbine wheel, the expansion ratio across the wheel essentially exhaust manifold pressure must increase to create the same power for the compressor.
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I think this is the problem in perspective. You are making a case for maintaining the same power for the compressor, then yes you will have to have more driving force. The others have looked at what happens when the gate opens - pressure must drop but they are not stating that they are maintaining the same compressor power. Both sides are right. Now let's get on to something completely different.
 
If you read my first post I said that (during acceleration)
You have to be decelerating when the wastegate opens. Therefore the boost is rising as the wastegate opens to stabilize the pressure not the wheel speed; the wheel speed will still increase to supply engine demand during acceleration.
As I said before if you look at a compressor map you will see that the wheel speed must increase to maintain at constant pressure as flow demand increases, (follow the speed line on the map) and you will see that it drops off.
 
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