Cam Qs...
05-15-2009, 09:54 PM
#11
I agree that on a daily driver, many times, less is more, and if you plan on staying with the stock converter, you'll want to keep your intake duration in check.
I'd like to hear the head porter's input also, it's always nice to have as much professional info as possible...you know what they say: "you learn something new every day"
I'd like to hear the head porter's input also, it's always nice to have as much professional info as possible...you know what they say: "you learn something new every day"
05-15-2009, 10:09 PM
#15
Here, read this and learn why reverse splits are a bad idea on an lsx engine.
This is a write up by Bret Bauer of Bauer Racing Engines:
--------------------------------------------------------------------------------
Preface.... The Reverse Split Ideology:
The whole "theory" on why LS engines need a reverse split, that being a cam with more intake duration than exhaust duration is as follows from what I take:
1. My Version: Since a LS motor for example has a 80% E/I ratio in bare form and then when a intake manifold is installed it increases that ratio even more so the exhaust is much more than 75% of the intake, we need to match the to camshaft that flow imbalance hence changing the duration to this configuration.
2. LS1Toke: A reverse split cam is best for someone who has limited mods on the intake side and good mods(such as LT, ORY, and cat-back) on the exhaust side.
3. LS1Toke: A reverse split cam is better for your current application if you don't have the best intake flow and if you have full exhaust. What it does is allow more air into the cylinders. So since you have a LS1 intake you would benefit from it because the flow isnt as good as LS6.
And the real kicker a "Advanced Tech" thread on the matter...
https://ls1tech.com/forums/showthread.php?t=925980
Ok so now I guess we have down that with a good exhaust system like a standard bolt on car has, you now have LOTS of exhaust flow after the head so it's not a restriction to the exhaust flow, but with the intake manifold design of the LS motor you have a choked off intake port since the manifold can't FLOW as much as the cylinder head. Therefore this makes the intake to exhaust ratio flow around something stupid like 90%.
Now on to why this is all horse hockey. (bonus points for who can tell me where I get that from)
Just the FACTS mam:
The people who stumble on this "theory" are comparing data from static flow testing only and basing their choices for a camshaft on things that don't really happen in the working motor.
The first rule here that this is a BS idea is the straight fact that the LS motor makes 100% VE or greater very easily. Engine dyno tests show that a stock LS6 motor for example will make 430HP in stock trim without the accessories on it. That's right at or above 100% VE. Now consider that if the LS6 cam is retarded 2° which is normal, the IVC is around 68° ABDC. So there is only 112° of time when the air/fuel is "trapped" in the cylinder, or 62% of 180°.
So how can a head that can flows 250+ cfm in stock form that is being choked off by a intake manifold make 100%+ VE on top of 346 cubes?
How does it do it in stock form, especially with all the stock cams being "traditional" split cams? 196/202, 201/210, 204/218, 204/211 etc....
The real problem here is that these guys are looking at FLOW, and not the depression or delta P, that is causing that flow in the first place. That leads to looking at the intake manifold, the same flow robbing bandit turns out to be the positive pressure producing part of the motor that is causing 100% VE in stock form! Yep our old buddy pressure wave tuning is rearing his ugly head to make this concept of flow irrelevant to the average Joe's easy thinking.
Pressure Wave Tuning the basic and expanded explaination:
Pressure waves are produced from a Helmholtz resonance, which has best been described as air acting like mass on a spring in the intake port from valve to plenum.
A excerpt from Wikipedia that is good on this...
"Qualitative explanation
When air is forced into a cavity, the pressure inside increases. Once the external force that forces the air into the cavity disappears, the higher-pressure air inside will flow out. However, this surge of air flowing out will tend to over-compensate, due to the inertia of the air in the neck, and the cavity will be left at a pressure slightly lower than the outside, causing air to be drawn back in. This process repeats with the magnitude of the pressure changes decreasing each time.
This effect is akin to that of a bungee-jumper bouncing on the end of a bungee rope, or a mass attached to a spring. Air trapped in the chamber acts as a spring. Changes in the dimensions of the chamber adjust the properties of the spring: a larger chamber would make for a weaker spring, and vice-versa.
The air in the port (the neck of the chamber) is the mass. Since it is in motion, it possesses some momentum. A longer port would make for a larger mass, and vice-versa. The diameter of the port is related to the mass of air and the volume of the chamber. A port that is too small in area for the chamber volume will "choke" the flow while one that is too large in area for the chamber volume tends to reduce the momentum of the air in the port."
Here is a easy to read article that relates this phenomenon closer to internal combustion engines... http://www.dinamoto.it/DINAMOTO/on-l...suonatore.html
Or if you feel like you want to a more direct explaination of all of this it can be found in a paper here titled: The Acoustics of Racing Engine Intake Systems
Very cool paper if you are into super geeky engine stuff!
How all of this works to make HP:
So now that we have the idea that pressure waves going back and fourth between the plenum and valve cause a building and dropping of pressure in the intake port. The tuning of this wave is relative to the length of the tract from plenum to valve and is either very good at certain RPM or very bad and also has a order as to how many times it cycles per engine revolution at that RPM. These are called harmonics....
Harmonics are the key to the strength of the pulse, by reading the excerpt above on Helmholtz resonance you can see that the pressure pulse is stronger the longer the runner. Now each RPM has a length associated with each harmonic. The harmonics going from one to six get weaker with every additional harmonic, the first being the strongest and longest, but you have to calculate the appropriate length relative to RPM and cylinder displacement.
A LS motor works on the 2nd Harmonic so it is a very strong, thus producing high pressure in the intake port. High pressure above a low cylinder pressure creates a large depression.... a lot like a flow bench makes. Now with that idea we can relate this to how the average Joe looks at head data.
This large difference or large depression causes the head to act like it is being flowed on a flow bench at a higher depression than the standard 28" of flow. It can be over 100" of depression on a stock LS6 at HP peak. So now the flow of the intake port in this dynamic environment is much more than the 250cfm or so that the flow bench tell us. Actually around .500" lift where the head statically flows 250cfm @ 28" on a flow bench it actually moves about 320cfm on the running motor.
The only issue with using these numbers is that from IVO to IVC the depression between the head port and cylinder changes and it does so at every RPM as well. Either way this points out that with the 2nd order harmonic that the LS motor works on we fill the cylinder much more than the flow bench data says we can. That's why we can fill the cylinder at or more than 100% VE on a stock motor hence how this all makes HP!
So how does this relate to the "split" of the cam?:
What you put into a motor you have to get out... now since time in camshaft terms is relative to duration we have to get out what we get in. Since there are no restrictions in the system to filling the cylinder and as we have seen the motor does so better than we can imagine due to resonance tuning.
The only issue with the resonance tuning is that it's highly sensitive to the intake valve timing and if we leave the valve open too long the motor will lose what it put into the cylinder (late IVC) or not create enough of a pressure build up to start filling the cylinder well at IVO, so that means we have a set intake duration range that is relative to our working RPM range we can use.... (hence why big cams are wrong for street cars!)
So now since we have a limit on the intake side of the cam since it's a compromise between optimal valve events for a range of RPM, we have to figure out what it takes to get out what the motor put in.
The exhaust side of the motor is much, much harder to guess at. The pressures are very high when the exhaust valve is cracked @ EVO and decays from there until EVC. The flow happening here makes very little sense if any at all to even the best in the industry and flow numbers of a static flow bench tell us little to if anything about what is going on.
Conclusion:
What we do know is that with the added depression that the intake port sees due to the 2nd harmonic pressure pulse we put more in the cylinder during the time the intake valve was open than what the cylinder head statically flows.... so we have to get all of that out, and get it out through a smaller hole!
This simple fact is why you need more duration on the exhaust than on the intake in a LS motor.
This is a write up by Bret Bauer of Bauer Racing Engines:
--------------------------------------------------------------------------------
Preface.... The Reverse Split Ideology:
The whole "theory" on why LS engines need a reverse split, that being a cam with more intake duration than exhaust duration is as follows from what I take:
1. My Version: Since a LS motor for example has a 80% E/I ratio in bare form and then when a intake manifold is installed it increases that ratio even more so the exhaust is much more than 75% of the intake, we need to match the to camshaft that flow imbalance hence changing the duration to this configuration.
2. LS1Toke: A reverse split cam is best for someone who has limited mods on the intake side and good mods(such as LT, ORY, and cat-back) on the exhaust side.
3. LS1Toke: A reverse split cam is better for your current application if you don't have the best intake flow and if you have full exhaust. What it does is allow more air into the cylinders. So since you have a LS1 intake you would benefit from it because the flow isnt as good as LS6.
And the real kicker a "Advanced Tech" thread on the matter...
https://ls1tech.com/forums/showthread.php?t=925980
Ok so now I guess we have down that with a good exhaust system like a standard bolt on car has, you now have LOTS of exhaust flow after the head so it's not a restriction to the exhaust flow, but with the intake manifold design of the LS motor you have a choked off intake port since the manifold can't FLOW as much as the cylinder head. Therefore this makes the intake to exhaust ratio flow around something stupid like 90%.
Now on to why this is all horse hockey. (bonus points for who can tell me where I get that from)
Just the FACTS mam:
The people who stumble on this "theory" are comparing data from static flow testing only and basing their choices for a camshaft on things that don't really happen in the working motor.
The first rule here that this is a BS idea is the straight fact that the LS motor makes 100% VE or greater very easily. Engine dyno tests show that a stock LS6 motor for example will make 430HP in stock trim without the accessories on it. That's right at or above 100% VE. Now consider that if the LS6 cam is retarded 2° which is normal, the IVC is around 68° ABDC. So there is only 112° of time when the air/fuel is "trapped" in the cylinder, or 62% of 180°.
So how can a head that can flows 250+ cfm in stock form that is being choked off by a intake manifold make 100%+ VE on top of 346 cubes?
How does it do it in stock form, especially with all the stock cams being "traditional" split cams? 196/202, 201/210, 204/218, 204/211 etc....
The real problem here is that these guys are looking at FLOW, and not the depression or delta P, that is causing that flow in the first place. That leads to looking at the intake manifold, the same flow robbing bandit turns out to be the positive pressure producing part of the motor that is causing 100% VE in stock form! Yep our old buddy pressure wave tuning is rearing his ugly head to make this concept of flow irrelevant to the average Joe's easy thinking.
Pressure Wave Tuning the basic and expanded explaination:
Pressure waves are produced from a Helmholtz resonance, which has best been described as air acting like mass on a spring in the intake port from valve to plenum.
A excerpt from Wikipedia that is good on this...
"Qualitative explanation
When air is forced into a cavity, the pressure inside increases. Once the external force that forces the air into the cavity disappears, the higher-pressure air inside will flow out. However, this surge of air flowing out will tend to over-compensate, due to the inertia of the air in the neck, and the cavity will be left at a pressure slightly lower than the outside, causing air to be drawn back in. This process repeats with the magnitude of the pressure changes decreasing each time.
This effect is akin to that of a bungee-jumper bouncing on the end of a bungee rope, or a mass attached to a spring. Air trapped in the chamber acts as a spring. Changes in the dimensions of the chamber adjust the properties of the spring: a larger chamber would make for a weaker spring, and vice-versa.
The air in the port (the neck of the chamber) is the mass. Since it is in motion, it possesses some momentum. A longer port would make for a larger mass, and vice-versa. The diameter of the port is related to the mass of air and the volume of the chamber. A port that is too small in area for the chamber volume will "choke" the flow while one that is too large in area for the chamber volume tends to reduce the momentum of the air in the port."
Here is a easy to read article that relates this phenomenon closer to internal combustion engines... http://www.dinamoto.it/DINAMOTO/on-l...suonatore.html
Or if you feel like you want to a more direct explaination of all of this it can be found in a paper here titled: The Acoustics of Racing Engine Intake Systems
Very cool paper if you are into super geeky engine stuff!
How all of this works to make HP:
So now that we have the idea that pressure waves going back and fourth between the plenum and valve cause a building and dropping of pressure in the intake port. The tuning of this wave is relative to the length of the tract from plenum to valve and is either very good at certain RPM or very bad and also has a order as to how many times it cycles per engine revolution at that RPM. These are called harmonics....
Harmonics are the key to the strength of the pulse, by reading the excerpt above on Helmholtz resonance you can see that the pressure pulse is stronger the longer the runner. Now each RPM has a length associated with each harmonic. The harmonics going from one to six get weaker with every additional harmonic, the first being the strongest and longest, but you have to calculate the appropriate length relative to RPM and cylinder displacement.
A LS motor works on the 2nd Harmonic so it is a very strong, thus producing high pressure in the intake port. High pressure above a low cylinder pressure creates a large depression.... a lot like a flow bench makes. Now with that idea we can relate this to how the average Joe looks at head data.
This large difference or large depression causes the head to act like it is being flowed on a flow bench at a higher depression than the standard 28" of flow. It can be over 100" of depression on a stock LS6 at HP peak. So now the flow of the intake port in this dynamic environment is much more than the 250cfm or so that the flow bench tell us. Actually around .500" lift where the head statically flows 250cfm @ 28" on a flow bench it actually moves about 320cfm on the running motor.
The only issue with using these numbers is that from IVO to IVC the depression between the head port and cylinder changes and it does so at every RPM as well. Either way this points out that with the 2nd order harmonic that the LS motor works on we fill the cylinder much more than the flow bench data says we can. That's why we can fill the cylinder at or more than 100% VE on a stock motor hence how this all makes HP!
So how does this relate to the "split" of the cam?:
What you put into a motor you have to get out... now since time in camshaft terms is relative to duration we have to get out what we get in. Since there are no restrictions in the system to filling the cylinder and as we have seen the motor does so better than we can imagine due to resonance tuning.
The only issue with the resonance tuning is that it's highly sensitive to the intake valve timing and if we leave the valve open too long the motor will lose what it put into the cylinder (late IVC) or not create enough of a pressure build up to start filling the cylinder well at IVO, so that means we have a set intake duration range that is relative to our working RPM range we can use.... (hence why big cams are wrong for street cars!)
So now since we have a limit on the intake side of the cam since it's a compromise between optimal valve events for a range of RPM, we have to figure out what it takes to get out what the motor put in.
The exhaust side of the motor is much, much harder to guess at. The pressures are very high when the exhaust valve is cracked @ EVO and decays from there until EVC. The flow happening here makes very little sense if any at all to even the best in the industry and flow numbers of a static flow bench tell us little to if anything about what is going on.
Conclusion:
What we do know is that with the added depression that the intake port sees due to the 2nd harmonic pressure pulse we put more in the cylinder during the time the intake valve was open than what the cylinder head statically flows.... so we have to get all of that out, and get it out through a smaller hole!
This simple fact is why you need more duration on the exhaust than on the intake in a LS motor.
I've always been confused as to why your old cam dropped off so much after 5k...I figured that those specs would flow to 5800 easily, and actually still make good power up to 6200ish no problem. Your theory of too much head flow does make sense though. Hopefully your new cam and intake will match your heads more the way you'd like
05-15-2009, 10:41 PM
#18
How do the 243s compare performance and flow wise to the 317s that I'll be using?
I sent an email to him, so hopefully he chimes in. If not, I am sure that he'll at least reply to me, and I will try to convey what he tells me. I am not contesting that the traditionally exhaust biased profiles work. What I am saying is that if he says it works, dyno proven, then I will probably stay with that choice.
I did pose a quesiton about another choice...something like a 216/220 .56x/.58x...something like that. Just arbritrary numbers, but those seem to me that they would jive with the stock converter, retain good driving manners (good enough to carry a newborn) while falling in line with the exhaust bias theory.
My only concern is that I don't want to have a peaky cam, I want to have a strong overall power producing cam. That brings a compromise of reduced peak power, but like I said, I would rather have cam that drives just like a stocker on steroids, as opposed to something that I have to hit 5800 to really feel the power kick in.
I hope this is making sence...and thanks for the info, I really appreciate it.
I sent an email to him, so hopefully he chimes in. If not, I am sure that he'll at least reply to me, and I will try to convey what he tells me. I am not contesting that the traditionally exhaust biased profiles work. What I am saying is that if he says it works, dyno proven, then I will probably stay with that choice.
I did pose a quesiton about another choice...something like a 216/220 .56x/.58x...something like that. Just arbritrary numbers, but those seem to me that they would jive with the stock converter, retain good driving manners (good enough to carry a newborn) while falling in line with the exhaust bias theory.
My only concern is that I don't want to have a peaky cam, I want to have a strong overall power producing cam. That brings a compromise of reduced peak power, but like I said, I would rather have cam that drives just like a stocker on steroids, as opposed to something that I have to hit 5800 to really feel the power kick in.
I hope this is making sence...and thanks for the info, I really appreciate it.
Last edited by 03 BLACKOUTSSS; 05-15-2009 at 10:50 PM.
05-15-2009, 11:20 PM
#19
Wish I could help you with the 243/317 flow comparison, but I'm not sure. I'm sure that Joe or somebody will chime in.
If you want a good all around cam that isn't peaky, stick with a small duration cam like the ones we're referring to (216/220 should be nice for a 6.), and go with a wider LSA, like 114-115. The smaller duration will bring the torque on sooner and the wider LSA will give you a broader torque and power band.
Stumbled across the thread for the ARH headers that are on sale....
https://www.performancetrucks.net/fo...d.php?t=440611
If you want a good all around cam that isn't peaky, stick with a small duration cam like the ones we're referring to (216/220 should be nice for a 6.), and go with a wider LSA, like 114-115. The smaller duration will bring the torque on sooner and the wider LSA will give you a broader torque and power band.
Stumbled across the thread for the ARH headers that are on sale....
https://www.performancetrucks.net/fo...d.php?t=440611
05-16-2009, 05:58 AM
#20
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You will find lots of dyno sheets with "x" cam that works well and put down good #'s. Only way to compare cams would be the same vehicle with a cam swap and no other changes (other than tuning for the new cam).
I have use the 218/214 .578/.578 114 LSA cam in lots of 6.0 trucks and TBSS. Huge increase in TQ and still pulls past 6000 with a smooth idle.
If wanting anything bigger and being OM with a lil more aggressive idle (still mild though), I have used the 222/218 .595/.595 113 LSA cam with great success. I have seen both installed in the same vehicle compared to several cams (Hot Cam, Comp 212/218, TR 224, etc) with better results.
I have seen lots of back to back tests and i am sold on the reverse split concept for most set ups and several other companies (LG being a big one) agree in what I do. Most do not give out cam specs to keep others from following along, they just hand you a cam and say "run this cam".
As far as the reverse split thing, you are trying to make the cylinders fill as much as possible with "CLEAN air", not just "air'. This all comes down to the timing events and what is going on (pressure waves, pulses and harmonic) in the intake tract, exhaust tract and inside cylinder.
The length of the intake runners has alot to do with it but for a given amount of overlap and all the different combinations, a wider LSA and slight reverse split is what works best for lots of low and mid range TQ with descent top end power (what most trucks and mildly geared/mildly stalled F body/Vettes are after).
The same intake duration with a conventional split (4-6 degrees larger on exhaust), can get you 5-8 more HP at 7000 RPM and 3-4 more HP/TQt at 6500 RPM while making the same power at 6000 RPM and less HP/TQ at EVERY RPM below that. The reverse split will get you 10 more HP/TQ at 5000 RPM and 30-40 HP/TQ at 2500 RPM. This is what accelerates the vehicle well.
Everyone has there own theories and it is interesting how they cam across there beliefs. Some have there theories because that si what everyone else is doing, some do it because there only experience witgh cams has showed good gains and there is no reason to try anything else or believe anuything could be better, some spend countless hours on Desk Top Dyno or other HP calculator software that has minimal inputs, etc, etc.
Some people purchase a GOOD software program (Dynomation 5) that has TONS of inputs and measured everything involved (intake manifold runner length, intake manifold cross section, intake manifold taper and cross section at plenum, Venturi diameter of intake and exhaust port, intake/exhaust port runner length, intake/exhaust port cross section, etc, etc, etc, etc and look at the pressure waves going through the engine and how things are working.
Once the program shows a cam with very good results, try it in the real world and you will see the same gains at avrious RPM as shown in the program. Once you see the results in th real world, how can you argue.
I am not trying to change peoples way of thinking on cams, etc. I am just trying to offer a very good working product at a fair price.
Lloyd
I have use the 218/214 .578/.578 114 LSA cam in lots of 6.0 trucks and TBSS. Huge increase in TQ and still pulls past 6000 with a smooth idle.
If wanting anything bigger and being OM with a lil more aggressive idle (still mild though), I have used the 222/218 .595/.595 113 LSA cam with great success. I have seen both installed in the same vehicle compared to several cams (Hot Cam, Comp 212/218, TR 224, etc) with better results.
I have seen lots of back to back tests and i am sold on the reverse split concept for most set ups and several other companies (LG being a big one) agree in what I do. Most do not give out cam specs to keep others from following along, they just hand you a cam and say "run this cam".
As far as the reverse split thing, you are trying to make the cylinders fill as much as possible with "CLEAN air", not just "air'. This all comes down to the timing events and what is going on (pressure waves, pulses and harmonic) in the intake tract, exhaust tract and inside cylinder.
The length of the intake runners has alot to do with it but for a given amount of overlap and all the different combinations, a wider LSA and slight reverse split is what works best for lots of low and mid range TQ with descent top end power (what most trucks and mildly geared/mildly stalled F body/Vettes are after).
The same intake duration with a conventional split (4-6 degrees larger on exhaust), can get you 5-8 more HP at 7000 RPM and 3-4 more HP/TQt at 6500 RPM while making the same power at 6000 RPM and less HP/TQ at EVERY RPM below that. The reverse split will get you 10 more HP/TQ at 5000 RPM and 30-40 HP/TQ at 2500 RPM. This is what accelerates the vehicle well.
Everyone has there own theories and it is interesting how they cam across there beliefs. Some have there theories because that si what everyone else is doing, some do it because there only experience witgh cams has showed good gains and there is no reason to try anything else or believe anuything could be better, some spend countless hours on Desk Top Dyno or other HP calculator software that has minimal inputs, etc, etc.
Some people purchase a GOOD software program (Dynomation 5) that has TONS of inputs and measured everything involved (intake manifold runner length, intake manifold cross section, intake manifold taper and cross section at plenum, Venturi diameter of intake and exhaust port, intake/exhaust port runner length, intake/exhaust port cross section, etc, etc, etc, etc and look at the pressure waves going through the engine and how things are working.
Once the program shows a cam with very good results, try it in the real world and you will see the same gains at avrious RPM as shown in the program. Once you see the results in th real world, how can you argue.
I am not trying to change peoples way of thinking on cams, etc. I am just trying to offer a very good working product at a fair price.
Lloyd