Are the L92/LS3 exhaust ports really weak?
02-10-2008, 07:05 AM
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Are the L92/LS3 exhaust ports really weak? if the L92/LS3 exhaust ports flow as bad as is believed,at least on the boards here,why did GM go with a smaller exhaust lobe for the LS3,as opposed to the 02 LS6?
02 LS6-218dur@.050/.547lift
08 LS3-211dur@.050/.525lift
discuss....
02 LS6-218dur@.050/.547lift
08 LS3-211dur@.050/.525lift
discuss....
02-10-2008, 03:19 PM
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Jon
02-10-2008, 09:17 PM
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I have no way to know what they're thinking about exactly, but I'll hazard to take a guess or two. First, I do agree with 66duce that they are thinking about more than numbers on a flow bench . . . probably a lot more than an average enthusiast could imagine.
They may be thinking about reversion, emissions, favoring torque over HP, corporate average fuel economy guidelines within GM that they are supposed to adhere to even though it's a performance vehicle . . . lot's of things. My biggest question with the L92/LS3 heads is why the intake runner volume is so large. Why would they want to kill the velocity of the intake with such a large runner for a production engine? Now the intake to exhaust flow ratio on these heads defy all conventional wisdom of modern head design. They have such an excellent combustion chamber and other design features, but for me it's the intakes that I don't understand. The exhaust side doesn't bother me as much for a standard production vehicle. If they were designing for a more ***** to the wall vehicle (which they aren't) they'd probably have the exhausts flowing around 230 CFM at .600" valve lift.
Steve
They may be thinking about reversion, emissions, favoring torque over HP, corporate average fuel economy guidelines within GM that they are supposed to adhere to even though it's a performance vehicle . . . lot's of things. My biggest question with the L92/LS3 heads is why the intake runner volume is so large. Why would they want to kill the velocity of the intake with such a large runner for a production engine? Now the intake to exhaust flow ratio on these heads defy all conventional wisdom of modern head design. They have such an excellent combustion chamber and other design features, but for me it's the intakes that I don't understand. The exhaust side doesn't bother me as much for a standard production vehicle. If they were designing for a more ***** to the wall vehicle (which they aren't) they'd probably have the exhausts flowing around 230 CFM at .600" valve lift.
Steve
02-11-2008, 08:34 AM
#5
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The exhaust valve size is 1.6" which is larger than the previous heads anyway. Exhaust pressure is significantly above atmos at valve open so traditional pressure flow numbers dont mean ****.
My 2p and guessing
My 2p and guessing
02-11-2008, 08:47 AM
#6
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I have no way to know what they're thinking about exactly, but I'll hazard to take a guess or two. First, I do agree with 66duce that they are thinking about more than numbers on a flow bench . . . probably a lot more than an average enthusiast could imagine.
They may be thinking about reversion, emissions, favoring torque over HP, corporate average fuel economy guidelines within GM that they are supposed to adhere to even though it's a performance vehicle . . . lot's of things. My biggest question with the L92/LS3 heads is why the intake runner volume is so large. Why would they want to kill the velocity of the intake with such a large runner for a production engine? Now the intake to exhaust flow ratio on these heads defy all conventional wisdom of modern head design. They have such an excellent combustion chamber and other design features, but for me it's the intakes that I don't understand. The exhaust side doesn't bother me as much for a standard production vehicle. If they were designing for a more ***** to the wall vehicle (which they aren't) they'd probably have the exhausts flowing around 230 CFM at .600" valve lift.
Steve
They may be thinking about reversion, emissions, favoring torque over HP, corporate average fuel economy guidelines within GM that they are supposed to adhere to even though it's a performance vehicle . . . lot's of things. My biggest question with the L92/LS3 heads is why the intake runner volume is so large. Why would they want to kill the velocity of the intake with such a large runner for a production engine? Now the intake to exhaust flow ratio on these heads defy all conventional wisdom of modern head design. They have such an excellent combustion chamber and other design features, but for me it's the intakes that I don't understand. The exhaust side doesn't bother me as much for a standard production vehicle. If they were designing for a more ***** to the wall vehicle (which they aren't) they'd probably have the exhausts flowing around 230 CFM at .600" valve lift.
Steve
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02-11-2008, 03:05 PM
#8
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I am just an observer, not a participant in GM or anyone else's port design. I don't want to pontificate any ideas that I may have, so I encourage people to keep thinking about why the ports and valve events are what they are.
Make the assumption that what GM is selling works fairly well. Now develop theories that explain why it works. Discuss those theories. Remember the theories do not change the facts. When your theory is at odds with the facts, find a new theory.
From what I have seen in the aftermarket, some folks seem to have figured things out enough that they can improve considerably on the OEM stuff...and some have not.
Jon
Make the assumption that what GM is selling works fairly well. Now develop theories that explain why it works. Discuss those theories. Remember the theories do not change the facts. When your theory is at odds with the facts, find a new theory.
From what I have seen in the aftermarket, some folks seem to have figured things out enough that they can improve considerably on the OEM stuff...and some have not.
Jon
02-11-2008, 03:59 PM
#9
I am just an observer, not a participant in GM or anyone else's port design. I don't want to pontificate any ideas that I may have, so I encourage people to keep thinking about why the ports and valve events are what they are.
Make the assumption that what GM is selling works fairly well. Now develop theories that explain why it works. Discuss those theories. Remember the theories do not change the facts. When your theory is at odds with the facts, find a new theory.
From what I have seen in the aftermarket, some folks seem to have figured things out enough that they can improve considerably on the OEM stuff...and some have not.
Jon
Make the assumption that what GM is selling works fairly well. Now develop theories that explain why it works. Discuss those theories. Remember the theories do not change the facts. When your theory is at odds with the facts, find a new theory.
From what I have seen in the aftermarket, some folks seem to have figured things out enough that they can improve considerably on the OEM stuff...and some have not.
Jon
subscribe to common theories.
02-11-2008, 05:21 PM
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I am just an observer, not a participant in GM or anyone else's port design. I don't want to pontificate any ideas that I may have, so I encourage people to keep thinking about why the ports and valve events are what they are.
Make the assumption that what GM is selling works fairly well. Now develop theories that explain why it works. Discuss those theories. Remember the theories do not change the facts. When your theory is at odds with the facts, find a new theory.
From what I have seen in the aftermarket, some folks seem to have figured things out enough that they can improve considerably on the OEM stuff...and some have not.
Jon
Make the assumption that what GM is selling works fairly well. Now develop theories that explain why it works. Discuss those theories. Remember the theories do not change the facts. When your theory is at odds with the facts, find a new theory.
From what I have seen in the aftermarket, some folks seem to have figured things out enough that they can improve considerably on the OEM stuff...and some have not.
Jon
but my understanding of airflow,on a flowbench or running engine,is very limited...so i could be way off here..any thoughts?
02-12-2008, 08:06 AM
#12
my theory on this is: the smaller exhaust valve/port has a lot of velocity,helping to draw the intake charge in,compensating,in a way,for the slower velocity of the big port/valve on the intake side..and the exhaust port actually flows pretty good until the higher lifts..i would think high lift flow on the exhaust is not as critical as on the intake,considering the blow down effect when the exhaust valve is cracked open..
but my understanding of airflow,on a flowbench or running engine,is very limited...so i could be way off here..any thoughts?
but my understanding of airflow,on a flowbench or running engine,is very limited...so i could be way off here..any thoughts?
Just a SWAG, but possibly the intake is SO GOOD that they have to limit the exhaust flow to prevent scavenging? The last thing GM wants is some of the intake charge goin straight thru. So open it later, and close it sooner.
Their (the GM engineers) primary concern has to be emissions. Even at the expense of performance. Secondary, longevity.
Wudaya think about that Old SStroker?
02-12-2008, 09:20 AM
#13
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Dont forget that no intake charge is going to get drawn in if the valve is still closed, which with emissions etc these days is more likely.
.. which raises an interesting point. Perhaps the large intake port with low initial velocity works nicely to minimise charge waste out the exhaust port? If velocity is low then its less likely to make it to and through the exhaust port by the time it closes in comparison to a racey small port, high velocity head?
I know these heads are designed with emissions in mind as I understand the combusion chamber was designed to require more timing to help burn completion.
.. which raises an interesting point. Perhaps the large intake port with low initial velocity works nicely to minimise charge waste out the exhaust port? If velocity is low then its less likely to make it to and through the exhaust port by the time it closes in comparison to a racey small port, high velocity head?
I know these heads are designed with emissions in mind as I understand the combusion chamber was designed to require more timing to help burn completion.
02-12-2008, 01:25 PM
#14
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I think I recall reading somewhere that the smaller exh port also allowed more heatsink material around the exhaust as well to keep temps under control. Not sure how relevant that is to the topic.
02-12-2008, 01:31 PM
#15
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02-12-2008, 10:32 PM
#16
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In spite of evidence to the contrary, 3.4.
It is only magic to those who do not understand why things are happening. However, "magic" may be more correct than some theories. No offense meant to anyone posting here, BTW.
If you had never studied any engines before seeing LS7 or L76/L92 heads would you be asking the same questions? Would you be giving the same answers? If not, why not?
Low emissions and good power are not necessarily mutually exclusive.
It is only magic to those who do not understand why things are happening. However, "magic" may be more correct than some theories. No offense meant to anyone posting here, BTW.
If you had never studied any engines before seeing LS7 or L76/L92 heads would you be asking the same questions? Would you be giving the same answers? If not, why not?
Low emissions and good power are not necessarily mutually exclusive.
02-13-2008, 03:38 AM
#17
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Very true, good clean combustion is always best, emissions usually suggest incomplete combustion or overzealous cylinder scavanging. A large valve and port will allow way more charge to enter under the right circumstances. Which its logic to assume this head is designed to achieve.
Anyway, instead of idiots like me making semi wild guesses about this stuff. How about some of you more experienced guys making some semi (or fully) educated guesses to add to the topic. Afterall its a public forum for the dissemination of information and education of all. Including the idiots amongst us
If there was nothing to learn none of us would be reading this.
Anyway, instead of idiots like me making semi wild guesses about this stuff. How about some of you more experienced guys making some semi (or fully) educated guesses to add to the topic. Afterall its a public forum for the dissemination of information and education of all. Including the idiots amongst us
If there was nothing to learn none of us would be reading this.
02-13-2008, 03:52 PM
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Very true, good clean combustion is always best, emissions usually suggest incomplete combustion or overzealous cylinder scavanging. A large valve and port will allow way more charge to enter under the right circumstances. Which its logic to assume this head is designed to achieve.
Anyway, instead of idiots like me making semi wild guesses about this stuff. How about some of you more experienced guys making some semi (or fully) educated guesses to add to the topic. Afterall its a public forum for the dissemination of information and education of all. Including the idiots amongst us
If there was nothing to learn none of us would be reading this.
Anyway, instead of idiots like me making semi wild guesses about this stuff. How about some of you more experienced guys making some semi (or fully) educated guesses to add to the topic. Afterall its a public forum for the dissemination of information and education of all. Including the idiots amongst us
If there was nothing to learn none of us would be reading this.
02-14-2008, 02:18 AM
#19
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Well knowledge of engines is freely available, but it still takes a good shop to build one right. Not sure why people dont want to discuss how the heads work. Still loads of missing information between that and an optimal camshaft, but I guess it does head in that direction.
Sad this forum does not attract that sort of response
Sad this forum does not attract that sort of response
02-14-2008, 08:43 AM
#20
The key here is the ports flow "bad" in respect to how well the intake flows. They do not flow "bad" by any means for a 6.2L stock engine. In fact the exhaust flows very "good" for a 6.2L. Early IVC is key for these heads