cathedral ports
Thank you for the link Old Geezer. That pro stock port looked crazy. Ok so if cathedral ports arnt making the port flow better, what is? Is it the valve angle? Properly sized ports whats the deal? I understand the Ls7 does not have cathedral shaped heads and flows a lot better then a Ls1 head so what is the key factor that makes that engine so much better. I am sure cam timing, exhaust tuning, and intake tuning play a role but i would think the head port would have the largest impact. Am i wrong to assume this? Thanks
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Joined: Apr 2005
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From: Brockport NY
When i say better i mean better then previous engines like Lt1 and SBC that is excluding the exotic heads you can buy for those platforms. Correct me if i am wrong in believing this?
What most people don't realize is that the intake manifold is just a standard rectangle port, and that the olny reason the head looks like is does is to get the injector pointed at the intake valve... The region of the head that is "cathedral" has nothing to do with the flow of the head once the intake is bolted on.
Look at your intake manifold once its removed. The stocker had standard rectangle ports with rubber o-rings around them. The injector goes into the intake on the side, but is far enough out that the heads require a cathedral style port to let the injector have better angle toward the valve.
So once your intak is bolted on your only flowing air thru a traditional style rectangular port, not the cathedral style. It was all about cleanance & injector tuning.
Now this can differ on aftermarket intake manifolds. For example my Aluminum Lingenfelter Weiand intake manifold has cathedral ports on it, but the base of the manifold is also different than stock & for the injectors to fir the intake requires this style port to get the injector in the proper placement.
well, as far as the heads, the only major change that I know of is the valve degree change from 23 degrees to 15 degrees. overall, the extra power came from many little revisions and redesigns of the traditional small block chevy; the ls1 was a billion dollar project within GM designed to replace and improve the traditional small block chevy motor. back to the heads, the valve angle change is important as it allowed for a newly designed set of ports that improved the airflow by a pretty considerable margin. some of the key points in this improvement had to do with the fact that they flow remarkably well for a set of heads with less than 200cc intake runners-
Port velocity, and Intake charge density
*edit* Please check the attatched links for better clarification of anything I have posted.
Port velocity is directly linked to the effectiveness of a head. it is the speed at which the air charge travels from the plenum of the intake, through the intake runner, through the head and into the cylinder for combustion. this burst of air that is fed to the cylinder upon every intake stroke is the intake charge. this term describes the air and the fuel it carries with it. a motor with an oversized set of heads and induction system will NOT produce significant power until the port velocity has reached an acceptable speed. in fact, many years ago it was common for a pro-stock street car to have the "bigger is better" approach to head ports. large, hollowed out caves were ported into a lot of motors. eventually someone found out that these large ports are lazy, they do flow a large cross sectional area of air, but they do it slowly, and with less density than a properly sculpted and sized intake tract.
as the RPMs rise in your motor, the air demand increases, and the time allowed for it to reach the cylinder is decreased. now, stop and think about how this might effect a performance motor- what would be the necessary air- handling qualities of a head to make good use of this short time frame? speed, and density of the intake charge, maybe? this is where port velocity comes into play. a properly sized port will be just large enough to provide the volume of air that you need for your maximum calculated power level. this will ensure that you reach an acceptable port velocity at as low of an rpm level as possible, and yet not stifle the motor's peak power potential. the port design refinements allowed for a useable-y sized port that maintained this velocity for good torque and efficiency while still allowing it to produce some pretty decent numbers
Be sure to scroll down to the area reguarding wave dynamics. It is in bold print and not easily missed.
http://en.wikipedia.org/wiki/Cylinder_head_porting
another link using david vizard as a source. If you do not know who david vizard is, you should. search for him on google. scroll halfway down this page and read the two paragraphs, "port flow vs. Velocity" and "swirl"
http://www.moparmusclemagazine.com/t...ads/index.html
now we enter intake charge density. with an excellent port velocity comes charge density. when you suck air and fuel through a head at a good intake port velocity, say around 600 FPS, you can use the head's intake port design to increase the density of the charge, which would effectively give you the advantage of a larger port volume, without actually having a larger port. this is inherent in almost all cylinder heads, but there was some gains made in the new ls1 port design. if you look at a cross-section of any cylinder head, you will notice that the entrance to the intake port is larger than the exit at the valve, where it enters the cylinder. the "vaccum" created at the cylinder produces a venturi effect where the air gains speed and stability as it travels through the intake port. there is a limit, however, at which point the intake charge velocity reaches a speed where the fuel literally puddles and drops out of the air mixture. along with tract reversion issues with the valve. i could be talking out of my #%$ here but If i remember correctly it is around 1300 fps.
Preview of a fantastic book for LS1's. start your reading at the top of page 71 and read halfway through. great book to buy. a bit outdated as far as aftermarket gear but still well worth the money.
http://books.google.com/books?id=57f...hl=en#PPA71,M1
in reference to your question, the two goals of a good head and specifically the intake port are to provide as much as as the engine needs, at the highest possible speed and density.
cylinder heads: valve angle, valve shrouding, and spark plug placement. also, other power adding features of the lsx design.
the 15 degree valve angle not only provides a straighter shot into the cylinder, but it also unshrouds the valves a bit more.
think about how the air must flow around the valve to get into the cylinder. most of your duration is at lower lifts, and even at a lift of around .6", there still isnt much room for the air to escape around the valve, which means that intake charge hits the back of the valve and flows outward into the cylinder. this brings up our next term, valve shrouding. when you have this intake charge flowing out around the valve, it will be impeded by the cylinder walls, the spark plug and the combustion chamber design. with a standard small block chevy 23 degree valve angle, the valve will get closer and closer to the cylinder wall. this is still happening with a 15 degree head, but not as much. as a side note, nascar heads run 18 degree valve angles.
another reason the heads produce more power has to do with spark plug placement. this is a huge factor in power production, as the combustion process inside of a motor has a limited amount of time to complete. and again, that time is short, less than a fraction of a second. the ignition and burn of a compressed mixture of gas and air occurs in an expanding, ball-like flame front. that said, if the spark plug is perfectly centered, the flame front has an equal distance to travel all the way around the cylinder bore. if it is slightly off center, one side has to travel farther than the other to get a complete burn. the result is a longer burn time, a slower expansion of the gases propelling the piston's downward movement, and less power. the ls1 has a very ideal spark plug placement compared to many of the older head designs. *edit* to further explain, this is revelent because you want to have the quickest burn possible to maximize your cylinder pressures as soon as possible on the doward power stroke of the piston. the very early stages of the combustion process are critical. the sooner you get a complete burn the better as you want to get as much combustion while the piston is close to the head. anything at all that can contribute to a more consistent, faster burn will have noticeable results.
Swirl is a rotational flow of the intake charge once it enters the cylinder. there is also a tumble rotation of air, with one running perpendicular and the other horizontally with the cylinder bore centerline. a high amount of this tumbling, swirling motion makes the gasses burn quicker due to better atomization and consistancy of the air /fuel mixture. the design of the combustion chamber will determine how well the head introduces this movement. in the case of the LS1, the flat, triangle shaped area where the spark plug enters the combustion chamber is responsible for much of the swirl introduced. another place for newer design to improve.
another great Vizard link that talks about and to McLaren racing about engine development. scroll halfway down and read from "Port Evolution" to "Exhaust port design."
http://www.enginebuildermag.com/Arti...ren_heads.aspx
the injection system is very ideal, by aiming the injectors at the back of the intake valve rather than injecting the fuel into the intake manifold and letting the air carry it through the bends and turns into the cylinder. the computer controlled spark timing and sequential injection timing is a major advancement compared to the bank-fire injection system on say, an older TPI style motor. a bank fire system fires all four injectors on one cylinder bank at the same time, and it begins to glob together as it waits for the intake charge to carry it into the cylinder. a sequential fire system like the ls1 fires the injector precisely when the motor needs it, which gives the benefit of better fuel atomization. the intake itself is also less restrictive and better built for higher rpms with shorter, better sculpted intake runners. the lt1 and TPI intake were both fairly restrictive- a standard dual-or single plane intake outflowed them by a pretty good margin. anything stock that says TPI should be melted down into beer cans- at least the ones that limit RPM at 5500.
there are also little things about the combustion chamber design that improve power, like eliminating hotspots that can pre-ignite the air/fuel mixture, resulting in detonation. the elimination of hotspots allows for higher compression ratios - *edit think cylinder pressures. valve angle jobs, valve bowl refinements etc. etc. again, all in all, its really a bunch of different refinements that made the power difference.
Port velocity, and Intake charge density
*edit* Please check the attatched links for better clarification of anything I have posted.
Port velocity is directly linked to the effectiveness of a head. it is the speed at which the air charge travels from the plenum of the intake, through the intake runner, through the head and into the cylinder for combustion. this burst of air that is fed to the cylinder upon every intake stroke is the intake charge. this term describes the air and the fuel it carries with it. a motor with an oversized set of heads and induction system will NOT produce significant power until the port velocity has reached an acceptable speed. in fact, many years ago it was common for a pro-stock street car to have the "bigger is better" approach to head ports. large, hollowed out caves were ported into a lot of motors. eventually someone found out that these large ports are lazy, they do flow a large cross sectional area of air, but they do it slowly, and with less density than a properly sculpted and sized intake tract.
as the RPMs rise in your motor, the air demand increases, and the time allowed for it to reach the cylinder is decreased. now, stop and think about how this might effect a performance motor- what would be the necessary air- handling qualities of a head to make good use of this short time frame? speed, and density of the intake charge, maybe? this is where port velocity comes into play. a properly sized port will be just large enough to provide the volume of air that you need for your maximum calculated power level. this will ensure that you reach an acceptable port velocity at as low of an rpm level as possible, and yet not stifle the motor's peak power potential. the port design refinements allowed for a useable-y sized port that maintained this velocity for good torque and efficiency while still allowing it to produce some pretty decent numbers
Be sure to scroll down to the area reguarding wave dynamics. It is in bold print and not easily missed.
http://en.wikipedia.org/wiki/Cylinder_head_porting
another link using david vizard as a source. If you do not know who david vizard is, you should. search for him on google. scroll halfway down this page and read the two paragraphs, "port flow vs. Velocity" and "swirl"
http://www.moparmusclemagazine.com/t...ads/index.html
now we enter intake charge density. with an excellent port velocity comes charge density. when you suck air and fuel through a head at a good intake port velocity, say around 600 FPS, you can use the head's intake port design to increase the density of the charge, which would effectively give you the advantage of a larger port volume, without actually having a larger port. this is inherent in almost all cylinder heads, but there was some gains made in the new ls1 port design. if you look at a cross-section of any cylinder head, you will notice that the entrance to the intake port is larger than the exit at the valve, where it enters the cylinder. the "vaccum" created at the cylinder produces a venturi effect where the air gains speed and stability as it travels through the intake port. there is a limit, however, at which point the intake charge velocity reaches a speed where the fuel literally puddles and drops out of the air mixture. along with tract reversion issues with the valve. i could be talking out of my #%$ here but If i remember correctly it is around 1300 fps.
Preview of a fantastic book for LS1's. start your reading at the top of page 71 and read halfway through. great book to buy. a bit outdated as far as aftermarket gear but still well worth the money.
http://books.google.com/books?id=57f...hl=en#PPA71,M1
in reference to your question, the two goals of a good head and specifically the intake port are to provide as much as as the engine needs, at the highest possible speed and density.
cylinder heads: valve angle, valve shrouding, and spark plug placement. also, other power adding features of the lsx design.
the 15 degree valve angle not only provides a straighter shot into the cylinder, but it also unshrouds the valves a bit more.
think about how the air must flow around the valve to get into the cylinder. most of your duration is at lower lifts, and even at a lift of around .6", there still isnt much room for the air to escape around the valve, which means that intake charge hits the back of the valve and flows outward into the cylinder. this brings up our next term, valve shrouding. when you have this intake charge flowing out around the valve, it will be impeded by the cylinder walls, the spark plug and the combustion chamber design. with a standard small block chevy 23 degree valve angle, the valve will get closer and closer to the cylinder wall. this is still happening with a 15 degree head, but not as much. as a side note, nascar heads run 18 degree valve angles.
another reason the heads produce more power has to do with spark plug placement. this is a huge factor in power production, as the combustion process inside of a motor has a limited amount of time to complete. and again, that time is short, less than a fraction of a second. the ignition and burn of a compressed mixture of gas and air occurs in an expanding, ball-like flame front. that said, if the spark plug is perfectly centered, the flame front has an equal distance to travel all the way around the cylinder bore. if it is slightly off center, one side has to travel farther than the other to get a complete burn. the result is a longer burn time, a slower expansion of the gases propelling the piston's downward movement, and less power. the ls1 has a very ideal spark plug placement compared to many of the older head designs. *edit* to further explain, this is revelent because you want to have the quickest burn possible to maximize your cylinder pressures as soon as possible on the doward power stroke of the piston. the very early stages of the combustion process are critical. the sooner you get a complete burn the better as you want to get as much combustion while the piston is close to the head. anything at all that can contribute to a more consistent, faster burn will have noticeable results.
Swirl is a rotational flow of the intake charge once it enters the cylinder. there is also a tumble rotation of air, with one running perpendicular and the other horizontally with the cylinder bore centerline. a high amount of this tumbling, swirling motion makes the gasses burn quicker due to better atomization and consistancy of the air /fuel mixture. the design of the combustion chamber will determine how well the head introduces this movement. in the case of the LS1, the flat, triangle shaped area where the spark plug enters the combustion chamber is responsible for much of the swirl introduced. another place for newer design to improve.
another great Vizard link that talks about and to McLaren racing about engine development. scroll halfway down and read from "Port Evolution" to "Exhaust port design."
http://www.enginebuildermag.com/Arti...ren_heads.aspx
the injection system is very ideal, by aiming the injectors at the back of the intake valve rather than injecting the fuel into the intake manifold and letting the air carry it through the bends and turns into the cylinder. the computer controlled spark timing and sequential injection timing is a major advancement compared to the bank-fire injection system on say, an older TPI style motor. a bank fire system fires all four injectors on one cylinder bank at the same time, and it begins to glob together as it waits for the intake charge to carry it into the cylinder. a sequential fire system like the ls1 fires the injector precisely when the motor needs it, which gives the benefit of better fuel atomization. the intake itself is also less restrictive and better built for higher rpms with shorter, better sculpted intake runners. the lt1 and TPI intake were both fairly restrictive- a standard dual-or single plane intake outflowed them by a pretty good margin. anything stock that says TPI should be melted down into beer cans- at least the ones that limit RPM at 5500.
there are also little things about the combustion chamber design that improve power, like eliminating hotspots that can pre-ignite the air/fuel mixture, resulting in detonation. the elimination of hotspots allows for higher compression ratios - *edit think cylinder pressures. valve angle jobs, valve bowl refinements etc. etc. again, all in all, its really a bunch of different refinements that made the power difference.
Last edited by nine-eight; Apr 3, 2008 at 10:33 PM.
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From: virginia
Thread Starter
Joined: Apr 2005
Posts: 1,456
Likes: 0
From: Brockport NY
There was some good points in there but some of the Lt1 facts are wrong. The Lt1 is SFI just like the Ls1 and the Lt1 actually has higher compression then the ls1 due to its reverse cooled cylinder heads. I get the point of all of the small refinements coming together to just make a overall better head. Thanks for the input.
http://books.google.com/books?id=mm8...hl=en#PPA88,M1
you are correct, I actually remember having someone tell me before that the LT1 did not have a bank fire system, that it was sequential. I have deleted that part from my original post, and thank you. the primary topic i was trying to cover with the above post had to do with the port velocity. the point of the topic is that the revised valve angle, combustion chamber and intake tract changes (that also mirror the exhaust tract changes) from the run of the mill 23 degree chevy head and its effects on port velocity and volumetric efficiency were probably the biggest contribution to the increased power output of the ls1 motors.
Glad you chimed in. I appreciate your helpful, constructive and thoughtful attention to the topic.
http://www.camaros.net/forums/archiv...p/t-18657.html
http://books.google.com/books?id=283...ptC0hfgk&hl=en
http://www.sportcompactcarweb.com/te...ead/index.html
There was some good points in there but some of the Lt1 facts are wrong. The Lt1 is SFI just like the Ls1 and the Lt1 actually has higher compression then the ls1 due to its reverse cooled cylinder heads. I get the point of all of the small refinements coming together to just make a overall better head. Thanks for the input.
http://www.camaros.net/forums/archiv...p/t-18657.html
http://books.google.com/books?id=283...ptC0hfgk&hl=en
http://www.sportcompactcarweb.com/te...ead/index.html
here I go, and pull up some information on the net to give some support to my post, and you post some chapped-*** remark about my knowledge coming from the internet. hell, you dont know a damn thing about me. yeah, I posted some internet links for you to read. what about it? what else do you want me to do, send you a book? post a photo of chuck norris holding a dyno sheet?
I guess McLaren engines and the likes of david vizard and smokey yunik are all intenet morons to you.I figured, this girl sure acts like she knows something everyone else doesnt. so I just typed your name in and found a few of your posts.
Then I saw that 80% or better of your posts are all just snide little remarks with no real substance. Kinda makes me think that maybe, you a troll? but nah, theres no real trolling going on. just some insults being thrown around. whether it be directed at ron @ vengeance racing or just some random guy on the board trying to learn something.
along with a "well... MY fecal matter emits NO odor" attitude and a few laughable huns, luvs, and honey thrown in, as "luv jessica" or "honey you cant handle it" remarks.
https://ls1tech.com/forums/showthrea...t=#post8715823
Wow and infinte wisdom coming out of your pie hole here.... sounds like you can regurgitate what every other moron on the boards "thinks" is good. I highly doubt YOU have ever touched a ET or All Pro head let alone ran one on the dyno against something else or even come close to making 1000hp in a LS2 block.
Oh yeah you READ about it on a internet forum. I forgot
Thank god I'm actually screwing someone who knows something. Knowledge thru injecton!
Jess
I'm guessing "someone" has "lied" to you before, poor boys. Someone = Hooker
Wow and infinte wisdom coming out of your pie hole here.... sounds like you can regurgitate what every other moron on the boards "thinks" is good. I highly doubt YOU have ever touched a ET or All Pro head let alone ran one on the dyno against something else or even come close to making 1000hp in a LS2 block.
Oh yeah you READ about it on a internet forum. I forgot
Thank god I'm actually screwing someone who knows something. Knowledge thru injecton!
Jess
I'm guessing "someone" has "lied" to you before, poor boys. Someone = Hooker
heh...you throw around more b*llshit than a dude ranch. your only qualifications seem to be a physics class and whatever you managed to pick up hanging around a shop. and maybe "Knowledge through injection."
I have ported my own heads. it isnt rocket science. aftermarket castings are stronger with more airlflow potential and its not worth my time porting them when in the same amount of time at work I could buy a set of CNC'd trickflows or AFR's.
FYI, You come off like an insecure little girl trying to validate her feelings of self-worth through shooting other people down as they try to share information and learn. you cut down people who may or may not be below the level of knowledge you have, when at one point you didnt even know where or what an oil filter was.
Well, have fun. I think ive had my fun with this post. the user wanted to find out what made the differences in power between two motors, and this isnt getting him any closer to the answer. I am done with this thread. and I sincerely wish you the best with your therapy sessions. maybe a few more trips a week is in order?
BTW, in your snide reply to predator-z, moron is spelled with two O's, honey. not that im insinuating anything.
Luv, 98.
Last edited by nine-eight; Apr 4, 2008 at 02:18 PM.
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Joined: May 2006
Posts: 132
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From: virginia
Good Job, now you can quote people on the internet AND bash a girl!
FWIW I do know what/where a oil filter is/goes, I just changed my own oil this weekend, I've also met David Vizzard before rather than just quote what he writes without understanding it.
You are right, you should be done with this thread rather than "helping" the orignal poster out you are confusing him with internet BS.
Jes
FWIW I do know what/where a oil filter is/goes, I just changed my own oil this weekend, I've also met David Vizzard before rather than just quote what he writes without understanding it.
You are right, you should be done with this thread rather than "helping" the orignal poster out you are confusing him with internet BS.
Jes
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
Good Job, now you can quote people on the internet AND bash a girl!
FWIW I do know what/where a oil filter is/goes, I just changed my own oil this weekend, I've also met David Vizzard before rather than just quote what he writes without understanding it.
You are right, you should be done with this thread rather than "helping" the orignal poster out you are confusing him with internet BS.
Jes
FWIW I do know what/where a oil filter is/goes, I just changed my own oil this weekend, I've also met David Vizzard before rather than just quote what he writes without understanding it.
You are right, you should be done with this thread rather than "helping" the orignal poster out you are confusing him with internet BS.
Jes
I do agree that there is some misinformation in this thread which I don't plan to address. I would advise the OP that this thread and wiki aren't the best places to learn about ports. Actually if one wants to learn why ports do or don't work you need to have a fairly rigorous background in some sciences. Unfortunately there are no simple answers to the complex questions about non-steady state airflow in engines.
Jditlfm I recommend Prof. Gordon Blair's writings on this subject, but it will make your head hurt at the very least. The first few times thru his stuff makes mine hurt. But eventually the Aaha! moments arrived.
Jon
Good Job, now you can quote people on the internet AND bash a girl!
FWIW I do know what/where a oil filter is/goes, I just changed my own oil this weekend, I've also met David Vizzard before rather than just quote what he writes without understanding it.
You are right, you should be done with this thread rather than "helping" the orignal poster out you are confusing him with internet BS.
Jes
FWIW I do know what/where a oil filter is/goes, I just changed my own oil this weekend, I've also met David Vizzard before rather than just quote what he writes without understanding it.
You are right, you should be done with this thread rather than "helping" the orignal poster out you are confusing him with internet BS.
Jes
when someone comes off like you do, it doesn't matter if you're male, female, or martian, you're going to get bashed.. with your comments you should expect it.
you aren't exactly helping anyone out in this thread either, other than arguing with someone that they didn't do it right.
maybe you should go throw your legs up in the air and get another "knowledge by injection" and come back and try to make a post with some substance?
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Joined: May 2006
Posts: 132
Likes: 0
From: virginia
Wow there is a serious amout of testosterone taking over for real thinking, typical men..... and thanks for the accusation that I'm a ****, I'm guessing you don't get laid much or the internet is the only place you have enough ***** to say such a thing. Either way when they tested my IQ I was 149 and I DIDN'T sleep with anyone to get that score.
Honestly the guys I know who do head porting wouldn't even bother posting up info because there are too many internet heros who couldn't absorb it and would rather argue with them about things they aren't going to understand.
Have fun boys, Jes
Honestly the guys I know who do head porting wouldn't even bother posting up info because there are too many internet heros who couldn't absorb it and would rather argue with them about things they aren't going to understand.
Have fun boys, Jes
Wow there is a serious amout of testosterone taking over for real thinking, typical men..... and thanks for the accusation that I'm a ****, I'm guessing you don't get laid much or the internet is the only place you have enough ***** to say such a thing. Either way when they tested my IQ I was 149 and I DIDN'T sleep with anyone to get that score.
Honestly the guys I know who do head porting wouldn't even bother posting up info because there are too many internet heros who couldn't absorb it and would rather argue with them about things they aren't going to understand.
Have fun boys, Jes
Honestly the guys I know who do head porting wouldn't even bother posting up info because there are too many internet heros who couldn't absorb it and would rather argue with them about things they aren't going to understand.
Have fun boys, Jes
it's easy to post smart *** comments,how about some real tech info?
