LS2 PCV Sucking Oil into Intake - Good Blog
03-25-2006, 09:48 PM
#1
LS2 PCV Sucking Oil into Intake - Good Blog
Here is link:
http://www.corvetteactioncenter.com/...5/sequel6.html
Here is section on Rings & PCV System:
New Rings and Revised Oil Control
The ring package has, once again, been changed. The top ring is still steel with a moly face and the second ring is still cast iron with a Napier face and they both are now 1.2-mm. wide, down from 1.5. The oil ring is still three-piece, two oil rails and an expander. The tension of all three rings is less than that used with the LS1/LS6 and the rings are more flexible.
The discussion with Jordan Lee and Mark Damico got interesting when I asked a question about the lower-tension rings. C5ers will recall the LS1/LS6 oil consumption fiasco that ended in a technical service bulletin fix. If you're unfamiliar with that, read http://www.idavette.net/hib/02ls6/page5.htm, then continue to read here.
CAC: Now, you guys went through the low-tension thing once before and then had to have a service bulletin fix for the ring flutter issue. How are you going to avoid that same scenario?
MD: Bore distortion is improved and the oil rails are thinner, so they're more compliant, so it takes less tension to get the same sealing.
CAC: How does bore distortion affect ring flutter?
MD: I don't know that it affects the flutter, but it's harder for the rings to seal when the shape's not round. Because we made the rings thinner, they're lighter, so they won't flutter until a higher engine speed.
CAC: My understanding is that with the later LS1 and LS6, the Napier-face, second improved oil control and eliminated that ring flutter problem.
MD: I don't know if I'd call it a "ring flutter problem.
CAC: This is an important point because John Juriga (Asst. Chief Engineer for passenger car Gen 3 engines from 1995-2003) was on record with media in May of 2001 stating that the reason the LS6 had an control problem was due to ring flutter.
MD: The issue was high engine speed at low MAP (manifold absolute pressure)...
CAC: And that was causing ring flutter. That was the explanation given. That's what I've published both in print and on the Internet. Was that not the problem?
MD: I don't remember it being "ring flutter" per se. We measure a characteristic called "blow-by", which is how much of the what you're putting into the cylinder to burn goes by the rings.
If blow-by goes up dramatically at a slight change in engine speed or load-everything's fine, then all of a sudden, it (ring seal) goes out of control-that's usually attributed to what's called "flutter." I don't remember us having that problem, but we definitely had increased oil consumption at high engine speeds and low MAP.
The other thing we ought to point out on the LS2 is the PCV system. There are two sides to it. There's the "fresh side", where air goes into the crankcase and then the "foul side" where air comes out.
You have oil separators on both sides. The separator on the foul side is the one that's the most important because that's where you have oil in the air. Blow-by goes in the crankcase then through the foul-side separator. The LS2 has a different design for that separator. It shares the same location (as Gen 3 parts) but internally, it's significantly different. Back to our CFD analysis and, actually, there's a spin on that that I think is proprietary to GM: analysis with droplets.
JL: "Rain drop analysis". During that separator design, there was a lot of sophisticated analysis done with a proprietary code. We were able to model the air and the oil through that chamber and develop baffles that would separate the oil from the air. It was quite a new technique and there aren't many companies that utilize it, today.
MD: It really helped us design the separator which, I think, was submitted for a patent.
JL: Yeah. The oil/air separator design is patented. When we talk about oil control, it's not only oil control in the pan to keep from sucking air-keep the pickup covered-we need oil control through the ventilation system.
You always want to separate the oil and drop it back into the crankcase and only burn the air. If you can't do that adequately, you're going to have high oil consumption. In the Gen 3s, when we had a lot of air moving through the PVC system at high speed, light load; the ventilation system didn't do a great job in separating the oil from the air so we ended-up burning some of the oil. That would manifest itself in higher oil consumption.
With Gen 4, we made significant improvements to that oil/air separator. We've also made significant improvements in lowering the amount of blow-by air under those conditions that caused the problems which Juriga referred to.
So we have two benefits here: 1) less blow-by through the crankcase under those conditions and 2) our separator is much more effective in separating the oil from the air, so we don't burn the oil. Our oil consumption is less as a result.
CAC: Why do you need an oil separator on the clean side of the system?
JL: On the clean side, in many instances, you have high blow-by at wide open throttle.
CAC: That air flow reverses?
JL: Yeah. You reach the capacity of the dirty air side to consume the air. You don't want to make the dirty air side so large you don't have to worry about the pressure side, but you don't want to consume a lot of crankcase air through the intake side of the engine all the time, either. You consume just enough that you're constantly purging the crankcase vapors adequately.
At light load, you have a little bit of help from manifold vacuum. You create that vacuum in the crankcase and it constantly purges the air and reduces sludge formation and it burns those hydrocarbons, which is a good thing.
When you go wide-open-throttle, high engine speed; you no longer have that vacuum to help pull the air from the crankcase and you, also, have more blow-by, so you may exceed the capacity of the dirty air side, which is sized for most normal light load engine operation.
You have to make sure your fresh air side, which starts to reverse-flow, does not blow oil and air out (into the intake). That's why we end-up having oil/air separation on both inlet and foul air sides.
CAC: In summary, it sounds like a lot of work was done on PCV, crankcase ventilation and oil control.
JL: That's right.
MD: Yeah.
http://www.corvetteactioncenter.com/...5/sequel6.html
Here is section on Rings & PCV System:
New Rings and Revised Oil Control
The ring package has, once again, been changed. The top ring is still steel with a moly face and the second ring is still cast iron with a Napier face and they both are now 1.2-mm. wide, down from 1.5. The oil ring is still three-piece, two oil rails and an expander. The tension of all three rings is less than that used with the LS1/LS6 and the rings are more flexible.
The discussion with Jordan Lee and Mark Damico got interesting when I asked a question about the lower-tension rings. C5ers will recall the LS1/LS6 oil consumption fiasco that ended in a technical service bulletin fix. If you're unfamiliar with that, read http://www.idavette.net/hib/02ls6/page5.htm, then continue to read here.
CAC: Now, you guys went through the low-tension thing once before and then had to have a service bulletin fix for the ring flutter issue. How are you going to avoid that same scenario?
MD: Bore distortion is improved and the oil rails are thinner, so they're more compliant, so it takes less tension to get the same sealing.
CAC: How does bore distortion affect ring flutter?
MD: I don't know that it affects the flutter, but it's harder for the rings to seal when the shape's not round. Because we made the rings thinner, they're lighter, so they won't flutter until a higher engine speed.
CAC: My understanding is that with the later LS1 and LS6, the Napier-face, second improved oil control and eliminated that ring flutter problem.
MD: I don't know if I'd call it a "ring flutter problem.
CAC: This is an important point because John Juriga (Asst. Chief Engineer for passenger car Gen 3 engines from 1995-2003) was on record with media in May of 2001 stating that the reason the LS6 had an control problem was due to ring flutter.
MD: The issue was high engine speed at low MAP (manifold absolute pressure)...
CAC: And that was causing ring flutter. That was the explanation given. That's what I've published both in print and on the Internet. Was that not the problem?
MD: I don't remember it being "ring flutter" per se. We measure a characteristic called "blow-by", which is how much of the what you're putting into the cylinder to burn goes by the rings.
If blow-by goes up dramatically at a slight change in engine speed or load-everything's fine, then all of a sudden, it (ring seal) goes out of control-that's usually attributed to what's called "flutter." I don't remember us having that problem, but we definitely had increased oil consumption at high engine speeds and low MAP.
The other thing we ought to point out on the LS2 is the PCV system. There are two sides to it. There's the "fresh side", where air goes into the crankcase and then the "foul side" where air comes out.
You have oil separators on both sides. The separator on the foul side is the one that's the most important because that's where you have oil in the air. Blow-by goes in the crankcase then through the foul-side separator. The LS2 has a different design for that separator. It shares the same location (as Gen 3 parts) but internally, it's significantly different. Back to our CFD analysis and, actually, there's a spin on that that I think is proprietary to GM: analysis with droplets.
JL: "Rain drop analysis". During that separator design, there was a lot of sophisticated analysis done with a proprietary code. We were able to model the air and the oil through that chamber and develop baffles that would separate the oil from the air. It was quite a new technique and there aren't many companies that utilize it, today.
MD: It really helped us design the separator which, I think, was submitted for a patent.
JL: Yeah. The oil/air separator design is patented. When we talk about oil control, it's not only oil control in the pan to keep from sucking air-keep the pickup covered-we need oil control through the ventilation system.
You always want to separate the oil and drop it back into the crankcase and only burn the air. If you can't do that adequately, you're going to have high oil consumption. In the Gen 3s, when we had a lot of air moving through the PVC system at high speed, light load; the ventilation system didn't do a great job in separating the oil from the air so we ended-up burning some of the oil. That would manifest itself in higher oil consumption.
With Gen 4, we made significant improvements to that oil/air separator. We've also made significant improvements in lowering the amount of blow-by air under those conditions that caused the problems which Juriga referred to.
So we have two benefits here: 1) less blow-by through the crankcase under those conditions and 2) our separator is much more effective in separating the oil from the air, so we don't burn the oil. Our oil consumption is less as a result.
CAC: Why do you need an oil separator on the clean side of the system?
JL: On the clean side, in many instances, you have high blow-by at wide open throttle.
CAC: That air flow reverses?
JL: Yeah. You reach the capacity of the dirty air side to consume the air. You don't want to make the dirty air side so large you don't have to worry about the pressure side, but you don't want to consume a lot of crankcase air through the intake side of the engine all the time, either. You consume just enough that you're constantly purging the crankcase vapors adequately.
At light load, you have a little bit of help from manifold vacuum. You create that vacuum in the crankcase and it constantly purges the air and reduces sludge formation and it burns those hydrocarbons, which is a good thing.
When you go wide-open-throttle, high engine speed; you no longer have that vacuum to help pull the air from the crankcase and you, also, have more blow-by, so you may exceed the capacity of the dirty air side, which is sized for most normal light load engine operation.
You have to make sure your fresh air side, which starts to reverse-flow, does not blow oil and air out (into the intake). That's why we end-up having oil/air separation on both inlet and foul air sides.
CAC: In summary, it sounds like a lot of work was done on PCV, crankcase ventilation and oil control.
JL: That's right.
MD: Yeah.
