Why LSA doesn't matter
07-24-2014, 12:17 AM
#21
HotRod has a good article that will that will also help out.
http://www.hotrod.com/techarticles/e...ne_angle_tech/
I'd also recommend going to all the major cam grinder/manufacture websites and looking for tech articles about understanding valve events. There's a lot of good info available online you just have to spend the time to look for it.
http://www.hotrod.com/techarticles/e...ne_angle_tech/
I'd also recommend going to all the major cam grinder/manufacture websites and looking for tech articles about understanding valve events. There's a lot of good info available online you just have to spend the time to look for it.
07-24-2014, 12:57 PM
#22
It's hard to generalize cam grinding especially when trying to teach the masses, but asking specific questions helps me to answer those questions as best I can.
07-24-2014, 01:31 PM
#23
This one is for the masses. How does IVC and EVO determine the powerband and how do you know when each will peak or carry. How does this change when you add cubic inches? Assuming were on a tight budget and given that most people go with 5/16th pushrods with ls7 lifters am I better off going with a mild lobe or an aggressive lobe when its been proven that light valves make power in themselves on a hydraulic roller setup even before valve float.
07-24-2014, 03:14 PM
#25
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This one is for the masses. How does IVC and EVO determine the powerband and how do you know when each will peak or carry. How does this change when you add cubic inches? Assuming were on a tight budget and given that most people go with 5/16th pushrods with ls7 lifters am I better off going with a mild lobe or an aggressive lobe when its been proven that light valves make power in themselves on a hydraulic roller setup even before valve float.
07-24-2014, 04:44 PM
#26
This one is for the masses. How does IVC and EVO determine the powerband and how do you know when each will peak or carry. How does this change when you add cubic inches? Assuming were on a tight budget and given that most people go with 5/16th pushrods with ls7 lifters am I better off going with a mild lobe or an aggressive lobe when its been proven that light valves make power in themselves on a hydraulic roller setup even before valve float.
Where the intake valve closes is closely related to where HP and TQ will peak in relation to RPM. IVO also plays a role in this as well. You cannot make up for cylinder fill that wasn't achieved on the intake stroke on the compression stroke by closing the intake valve later. The IVO event is what gets things going on the intake stroke and gets momentum started in the intake tract. Of course where the exhaust valve closes and where overlap ends determines this as well. Resonance tuning at its finest indeed. That is another topic for another discussion though.
The intake tracts minimum cross sectional area, flange area, the intake tracts length(cylinder head and intake manifold), local velocities, low lift flow numbers, piston speed and compression to name a few will determine where the intake valve needs to close. These variables will also have a large affect in and of themselves aside from the IVC event as to where peak HP and TQ is made in the operating range. You cannot force an engine to peak at an RPM that the induction or exhaust system will not allow. I've seen cam grinders and enthusiasts try to add more and more duration in an attempt to gain a higher peak power RPM only to fail time and time again when the induction and/or exhaust system will not allow it. The cam merely accentuates the power curves where as the induction and exhaust system play a much larger role in setting the RPM where peak power occurs.
Where the exhaust valve opens and how long the piston is given to "blow down" and how long the exhaust port is given to evacuate the cylinder is part of determining how far power will carry into the operating range. This event can help to shape the torque curve as well.
How does IVC and EVO affect where peak power is made?
Air has mass. Air is not weightless although it may seem that way. In our day to day lives we rarely stop to think that the air we're breathing actually weighs something as air is invisible to the naked eye.
Since air has mass, as it gains momentum and gains velocity in the intake tract it gains inertia. Because of this inertia when the piston begins its rise from bottom dead center to top dead center on the compression stroke air does not cease to flow into the cylinder immediately. You would think that because the piston is now pushing upwards that it would instantly push the mass out of the cylinder. This is not true though.
How long that air mass can carry enough inertia to continue to fill the cylinder while the piston rises to TDC directly influences when the intake valve close event should occur. I won't get into what design factors influence forward intake flow before reversion occurs on the compression stroke right now as that is another lesson all by itself.
As the piston moves faster and faster(higher piston speed) the intake and exhaust ports have less time to fill and exhaust the cylinder. Because of this, the intake valve must close later to achieve optimum cylinder fill and the highest VE possible.
RPM is not the only factor that influences piston speed though! The stroke of the engine and engine rpm is what determines piston speed. Rod length does not change the actual maximum piston speed, but it does change the acceleration of the piston as it goes past TDC and BDC. As stroke increases it has the exact same affect on cam timing as increasing the RPM of the engine without ever increasing engine RPM. In general a longer stroke crank needs a later intake valve close event versus a shorter stroke crank. I won't get into what physics are behind the longer stroke necessitating a later close.
If we have optimized cam timing for a given length stroke and piston speed, but that stroke now becomes longer or the RPM increases, the cam timing must also change to become optimum once again. On average I will make the IVC event 4-6 crank degrees later when comparing a 3.622" stroke crankshaft to a 4.0" stroke crankshaft. That isn't always set in stone 100%, but for the most part it's true. Now, the question that was asked, "How do we know where it will peak for a given IVC or EVO event"? That is something I don't want to get into without some further discussion occurring first. There are a ton of physics involved regarding the design of the intake and exhaust tracts that influence this way more than I can type out right now and attempt to explain.
I mentioned earlier about piston speed and it increasing. It gives the ports less time to do their job. Thus duration must increase and/or the lobe centers must widen to allow the events to stay optimum for the combination to perform best. So as piston speed increases whether by RPM or by increasing stroke, the exhaust valve must open sooner. Whether by adding duration or by widening the lobe centers. Again, if cam timing is optimized before the piston speed changes, I'll add 4-6 crank degrees going from a 3.622" stroke to a 4.0" stroke.
A higher compression engine should also have an earlier EVO event than a low compression engine. Higher compression engines drop cylinder pressure much sooner after the combustion event has occurred. Lower compression engines drop cylinder pressure slower after the combustion event has occurred. Since a higher compression engine has more cylinder pressure occurring earlier on the power stroke the added pressure is doing more work in a shorter amount of time than a lower compression engine. Because of this we can put more torque to the crank in a much shorter period of crank degrees. If you wait too late to open the exhaust valve in a high compression engine you're just wasting potential at the higher end of the operating range.
In a lower compression engine the amount of torque put to the crank is less in a shorter period of time so to attempt to even come close to doing the same amount of work as the high compression engine, that work must occur over a longer period of time. This necessitates a longer power stroke. This means that you have to choose whether you want to make torque on the bottom end and have power not carry as far due to a later opening EVO event. Or lose torque on the bottom end and have torque carry further with an earlier opening exhaust event. With a higher compression engine we can make more torque on the bottom end and carry torque further up top due to the earlier evo event that can be utilized.
The IVC event also can alter how much cylinder pressure is present. Don't get caught up in dynamic compression calculations though. A DCR calculation is really only good for cranking compression. As RPM rises and piston speed rises we are trapping more and more air mass in the cylinder. Since air has mass when it is compressed it creates pressure. So as RPM rises the engine produces more and more cylinder pressure up to the RPM where peak torque is produced. After peak torque(and peak VE subsequently) cylinder pressure begins to fall. At peak torque the highest amount of air mass is entering the engine so this will be the highest point of cylinder pressure the engine produces. Don't build an engine based on DCR. There are certain DCR's that work best with certain fuels and yes you can manipulate it somewhat, but for the most part it is a dynamic formula for a static measurement. In fact, making the IVC event later in an attempt to lower DCR to work with a given fuel octane may even raise cylinder pressure higher at peak torque making detonation worse.
As far as knowing where a given IVC/EVO event will allow an engine to peak or carry, a more specific example would need to be given. For the most part and in general though, a later IVC event means power will peak later and less bottom end torque will be generated with more high end HP. The same can be said for an earlier opening EVO event.
As far as whether to use a mild lobe or an aggressive lobe when utilizing 5/16" push rods, LS7 lifters and lightweight valves. A few other variables would need to be nailed down first before a decision could be made.
At what RPM does the combination operate? What is the weight of the valves? Seated and open pressure of the valve springs?
In general though, if we were comparing two combinations. One with solid stem valves, LS7 lifters and 5/16" push rods. Versus hollow stem valves with LS7 lifters and 5/16" push rods. I would normally use a more aggressive ramp rate with the lighter weight valves. A LS engine utilizing stock rocker arms can get away with a lot more than a LS engine utilizing roller rocker arms in this regard. The stock rocker arms allow a cam grinder to utilize a wider range of lobe profiles from mild to aggressive as the moment of inertia for a stock rocker arm is very low. This means that very little of the rocker arms mass is placed over the valve allowing better valve control even with more aggressive ramp rates.
Hopefully this answers Alwaystoslow question and sparks some more questions to be answered. I'll try to answer questions as soon as I can and to the best of my ability. Just keep them specific and clear so the discussion can stay focused on each topic and specific scenario.
07-24-2014, 05:06 PM
#27
So glad to see you lay all this out Martin. I was literally writing all the same stuff up for a sticky for the carb section and if you will allow me to quote this, you will save me a bunch of work.
I think explaining this in such a way that your average racer/rodder can visualize it is the hardest part. I am most glad that you talked about mass. That is the part that I think makes the visualization all come together. Understanding that the mass of air and fuel rushing in to filling the cylinder is like compressing a spring. We want to close the intake valve at close to the exact moment the spring is most compressed (most air and fuel in the cylinder) before it springs back and pushes the air and fuel back out of the cylinder. I think that visualization really works.
In a previous conversation with Martin, I had taken a similar position. My argument was that it is just different ways to express the exact same thing. And, that you could get to the same place regardless of the method that you used to express it.
I have since came to see it the way Martin does. The reason is, when I really started comparing successful combos using the exact valve events, I saw correlations in valve events that I would not have realized using duration/LSA/advance definitions. Having IVO IVC EVO EVC is just so much easier to visualize what you are actually doing compared to duration/LSA/advance.
I think explaining this in such a way that your average racer/rodder can visualize it is the hardest part. I am most glad that you talked about mass. That is the part that I think makes the visualization all come together. Understanding that the mass of air and fuel rushing in to filling the cylinder is like compressing a spring. We want to close the intake valve at close to the exact moment the spring is most compressed (most air and fuel in the cylinder) before it springs back and pushes the air and fuel back out of the cylinder. I think that visualization really works.
The only thing I would mention is to be careful about saying LSA doesnt matter...it is true the actual number isnt important, but as you pointed out, valve overlap is very important. Where you can run into trouble is you do not have any information about valve overlap without knowing LSA. So to say LSA is not important or doesnt matter is not exactly correct. Overall good beginner info though.
I have since came to see it the way Martin does. The reason is, when I really started comparing successful combos using the exact valve events, I saw correlations in valve events that I would not have realized using duration/LSA/advance definitions. Having IVO IVC EVO EVC is just so much easier to visualize what you are actually doing compared to duration/LSA/advance.
Last edited by speedtigger; 07-24-2014 at 05:21 PM.
07-24-2014, 05:17 PM
#28
So glad to see you lay all this out Martin. I was literally writing all the same stuff up for a sticky for the carb section and if you will allow me to quote this, you will save me a bunch of work.
I think explaining this in such a way that your average racer/rodder can visualize it is the hardest part. I am most glad that you talked about mass. That is the part that I think makes the visualization all come together. Understanding that the mass of air and fuel rushing in to filling the cylinder is like compressing a spring. We want to close the intake valve at close to the exact moment the spring is most compressed (most air and fuel in the cylinder) before it springs back and pushes the air and fuel back out of the cylinder. I think that visualization really works.
I think explaining this in such a way that your average racer/rodder can visualize it is the hardest part. I am most glad that you talked about mass. That is the part that I think makes the visualization all come together. Understanding that the mass of air and fuel rushing in to filling the cylinder is like compressing a spring. We want to close the intake valve at close to the exact moment the spring is most compressed (most air and fuel in the cylinder) before it springs back and pushes the air and fuel back out of the cylinder. I think that visualization really works.
You are more than welcome to put this on whatever forum here you wish.
I think your visualization is better than any I could ever come up with! Most excellent sir.
07-24-2014, 05:32 PM
#29
Great info here Martin.
I feel that too many people in the LS community buy a camshaft solely based off of "114 or 112" LSA, rather than the camshafts overall valve events and performance.
Cam going in my car right now is a 108. LSA is just a number
I feel that too many people in the LS community buy a camshaft solely based off of "114 or 112" LSA, rather than the camshafts overall valve events and performance.
Cam going in my car right now is a 108. LSA is just a number
07-24-2014, 10:01 PM
#31
If the valve events landed the LSA to be tighter, wouldn't that mean more overlap? And spreading them out cause less overlap? Is this why people think that a tighter LSA will lope more?
07-25-2014, 08:05 AM
#32
I've been meaning to make this thread for a long time. The main reason I want to make this thread is to educate anyone out there who may be curious about cam specs and valve events and that wants to become better educated on how and why camshafts are specified. This may also be good for those of you who are planning on purchasing a camshaft soon, but are confused by the many variants of camshafts available that may all seem similar, but have different LSA and slightly different duration. Hopefully even the more seasoned veterans on this site that have been doing this for a long time will find this information valuable. So with that said, here goes nothing.
I feel like to explain this best, I need to first explain how I choose a camshaft. At least paraphrase it somewhat to the extent of this thread's purpose. I won't go through everything, but I'll start with the very first thing I do when I begin to spec a camshaft.
I do not select a camshaft based on duration nor do I select it based on LSA. Whenever I have one of you guys on the phone or I'm reading your email that you've sent with specifications of your combination listed, I am thinking of a certain set of valve events that I feel will perform best for the combination. Now, that is not to say I do not have a good idea of what duration and LSA will be, but until I hammer out the events I really do not care what they end up at. If the events are right, the duration and LSA will be right.
Once I have selected the valve events I feel are best for the combination, I use a valve event calculator to compute those valve events into intake duration, exhaust duration, intake center line and exhaust center line. I could do the math manually, but it's much simpler and easier to do it with a valve event calculator.
Here is the meat and potatoes on LSA and why it doesn't matter now that I've got that out of the way. LSA is just a number. It is a sum of numbers. Although the LSA is fixed to the camshaft used in a LS engine and cannot be altered once ground, it is not actually "ground into" the camshaft. It is merely a sum of numbers as I said above. The intake and exhaust "lobe centers" or the "lobe center lines" are what really matters along with the duration of the intake and exhaust lobe.
Now let me show you how LSA is computed from a sum of numbers. Take for example our SNS Stage 2 camshaft. Its specs are 227/235 .614/.621 110+3. Let's take a look at what 110+3 really means. This means that for this given camshaft, the intake center line is 107 and the exhaust center line is 113. What does this mean exactly? Let's first look at what center lines on a camshaft are.
The intake center line is the point on the intake lobe where maximum lobe lift is reached. I won't get into asymmetrical cams and how this changes in that instance, but for now lets just assume that the above is true in all instances. The exhaust center line is the point on the exhaust lobe where maximum lobe lift is reached. Again, let's just assume that all cam lobes are symmetrical for the purpose of this discussion.
So if we have a 107 intake center line this means that 107 crank degrees after top dead center the intake lobe is at max lift. If we have a 113 exhaust center line this means that 113 crank degrees before top dead center the exhaust lobe is at max lift.
With that out of the way we can now compute the LSA of the camshaft. Once we have our center lines and we know what they are, we now know for any given cylinder(1,2,3,4,5,6,7 or 8) that the intake and exhaust lobes max lift occur 220 crank degrees apart from one another. How do I know this? I'll show you.
If you take the 107 icl and the 113 ecl and add them together, you get 220 crank degrees of lobe separation. Lobe centers or lobe center lines are expressed in crank degrees while LSA is expressed in cam degrees. So this means that on any given cylinder in our LS engine with the SNS Stage 2 camshaft installed, max intake lobe lift and max exhaust lobe lift occur 220 crank degrees apart from one another.
Since the crankshaft rotates 2 full revolutions for every 1 cam revolution, to compute the lobe separation to cam degrees we take 220 and divide it by 2. This gives us 110. So 110 cam degrees of rotation occurs between the intake lobe's max lift and the exhaust lobe's max lift. This means that on any given cylinder in a LS engine with the SNS Stage 2 camshaft installed that the intake and exhaust max lobe lift is separated 110 cam degrees apart from one another.
That is ALL that it means.
I also get the question all the time, "will this cam chop"? Or, "I'm afraid that because this cam is on a 114lsa it won't chop". This is internet myth and I will debunk it here for you.
LSA as I have shown is nothing but a sum of numbers. Overlap is what determines how much your cam will chop in a given engine. Cubic inches and a few other factors can change how much it chops, but for the majority more overlap means more chop and less overlap means less chop.
Now that you know what center lines are, think about a camshaft mentally in your mind. Look at how the centers of the lobes are spread apart from one another. If the LSA is tighter they will be closer to one another and if the LSA is wider they will be spread further from one another. If you took those centers and spread them apart further from one another, what would happen to the intake opening and exhaust closing ramps? They would now overlap less. I'll give an example.
Take the SNS Stage 2 cam 107 and 113 centers. If we change the exhaust center to a 115, we now have changed the LSA to a 111lsa. We didn't touch the duration of the intake or exhaust lobes, we just widened the exhaust center line. By doing this, and widening the centers further apart we reduce overlap. The SNS Stage 2 has 11 degrees of overlap @.050 lobe lift. If we change it to a 111lsa by doing the above, we now have 9 degrees of overlap@.050 lobe lift.
Now here is the real eye opener. If two camshafts no matter their duration or LSA both have the same amount of overlap and you put both cams in the exact same vehicle with everything else the same aside from the camshafts they will sound identical.
Let's take another cam for this example. 235/251 116+5. This cam has a 111 icl and a 121 ecl. Now most of you would probably say that because this camshaft has a 116lsa that it will not chop nearly as hard as the 110lsa of the SNS Stage 2. Let's take a closer look at how much overlap this cam actually has.
To determine overlap we add the intake and exhaust durations together and then divide them by two. This gives us 243. We now take the LSA and multiply it by 2 this gives us 232. Now subtract 243-232 = 11 degrees of overlap. So this camshaft has just as much overlap as the SNS Stage 2 with a 110lsa.
If you had the SNS Stage 2 cam installed in your car and replaced it with the 235/251 116lsa cam it would sound 100% identical to the SNS camshaft that you previously had installed. Again, LSA is just a sum of numbers and it doesn't matter!
I will leave this thread with one last suggestion. Do not pick a cam based on LSA. LSA is not the end all be all when it comes to camshaft performance or sound. Don't be lured into a trap by a manufacturer or a vendor when they tell you that, "X companies camshaft won't sound like you want it to because it's ground on a certain LSA". If you really want to know how two different camshafts will sound and want to see which one will chop harder at idle, just compare their overlap figures. If one has more overlap than the other it will chop harder than the other 95% of the time. If one has less overlap than the other it will chop less 95% of the time. Different exhaust systems and tuning can and will affect this, but for the most part overlap is a very good way in determining cam sound AND how drivable a camshaft will be. Don't think that just because a cam is ground on a tight LSA that it will be a pain to drive or because it's ground on a wide LSA that it will be a dream to drive.
I hope I have now instilled in those of you that read this that camshafts are just a sum of numbers. There are no absolutes in cam grinding. Everything is a compromise and not everything is as it seems at face value. Look deeper into your cam selections and compare valve events, overlap figures and not just duration and LSA specs. Compare the known performance of other camshafts with similar overlap and valve events to the cam you're considering purchasing. This will give much more insight into what you're looking for rather than just basing an assumption of LSA and duration.
I know that some of you already may know what I have put here, and that some of you may find this boring and not intriguing. For those that did not know this information I hope that after reading this thread you are better informed about your future or past purchases and are better informed into the how and the why cams do what they do.
I feel like to explain this best, I need to first explain how I choose a camshaft. At least paraphrase it somewhat to the extent of this thread's purpose. I won't go through everything, but I'll start with the very first thing I do when I begin to spec a camshaft.
I do not select a camshaft based on duration nor do I select it based on LSA. Whenever I have one of you guys on the phone or I'm reading your email that you've sent with specifications of your combination listed, I am thinking of a certain set of valve events that I feel will perform best for the combination. Now, that is not to say I do not have a good idea of what duration and LSA will be, but until I hammer out the events I really do not care what they end up at. If the events are right, the duration and LSA will be right.
Once I have selected the valve events I feel are best for the combination, I use a valve event calculator to compute those valve events into intake duration, exhaust duration, intake center line and exhaust center line. I could do the math manually, but it's much simpler and easier to do it with a valve event calculator.
Here is the meat and potatoes on LSA and why it doesn't matter now that I've got that out of the way. LSA is just a number. It is a sum of numbers. Although the LSA is fixed to the camshaft used in a LS engine and cannot be altered once ground, it is not actually "ground into" the camshaft. It is merely a sum of numbers as I said above. The intake and exhaust "lobe centers" or the "lobe center lines" are what really matters along with the duration of the intake and exhaust lobe.
Now let me show you how LSA is computed from a sum of numbers. Take for example our SNS Stage 2 camshaft. Its specs are 227/235 .614/.621 110+3. Let's take a look at what 110+3 really means. This means that for this given camshaft, the intake center line is 107 and the exhaust center line is 113. What does this mean exactly? Let's first look at what center lines on a camshaft are.
The intake center line is the point on the intake lobe where maximum lobe lift is reached. I won't get into asymmetrical cams and how this changes in that instance, but for now lets just assume that the above is true in all instances. The exhaust center line is the point on the exhaust lobe where maximum lobe lift is reached. Again, let's just assume that all cam lobes are symmetrical for the purpose of this discussion.
So if we have a 107 intake center line this means that 107 crank degrees after top dead center the intake lobe is at max lift. If we have a 113 exhaust center line this means that 113 crank degrees before top dead center the exhaust lobe is at max lift.
With that out of the way we can now compute the LSA of the camshaft. Once we have our center lines and we know what they are, we now know for any given cylinder(1,2,3,4,5,6,7 or 8) that the intake and exhaust lobes max lift occur 220 crank degrees apart from one another. How do I know this? I'll show you.
If you take the 107 icl and the 113 ecl and add them together, you get 220 crank degrees of lobe separation. Lobe centers or lobe center lines are expressed in crank degrees while LSA is expressed in cam degrees. So this means that on any given cylinder in our LS engine with the SNS Stage 2 camshaft installed, max intake lobe lift and max exhaust lobe lift occur 220 crank degrees apart from one another.
Since the crankshaft rotates 2 full revolutions for every 1 cam revolution, to compute the lobe separation to cam degrees we take 220 and divide it by 2. This gives us 110. So 110 cam degrees of rotation occurs between the intake lobe's max lift and the exhaust lobe's max lift. This means that on any given cylinder in a LS engine with the SNS Stage 2 camshaft installed that the intake and exhaust max lobe lift is separated 110 cam degrees apart from one another.
That is ALL that it means.
I also get the question all the time, "will this cam chop"? Or, "I'm afraid that because this cam is on a 114lsa it won't chop". This is internet myth and I will debunk it here for you.
LSA as I have shown is nothing but a sum of numbers. Overlap is what determines how much your cam will chop in a given engine. Cubic inches and a few other factors can change how much it chops, but for the majority more overlap means more chop and less overlap means less chop.
Now that you know what center lines are, think about a camshaft mentally in your mind. Look at how the centers of the lobes are spread apart from one another. If the LSA is tighter they will be closer to one another and if the LSA is wider they will be spread further from one another. If you took those centers and spread them apart further from one another, what would happen to the intake opening and exhaust closing ramps? They would now overlap less. I'll give an example.
Take the SNS Stage 2 cam 107 and 113 centers. If we change the exhaust center to a 115, we now have changed the LSA to a 111lsa. We didn't touch the duration of the intake or exhaust lobes, we just widened the exhaust center line. By doing this, and widening the centers further apart we reduce overlap. The SNS Stage 2 has 11 degrees of overlap @.050 lobe lift. If we change it to a 111lsa by doing the above, we now have 9 degrees of overlap@.050 lobe lift.
Now here is the real eye opener. If two camshafts no matter their duration or LSA both have the same amount of overlap and you put both cams in the exact same vehicle with everything else the same aside from the camshafts they will sound identical.
Let's take another cam for this example. 235/251 116+5. This cam has a 111 icl and a 121 ecl. Now most of you would probably say that because this camshaft has a 116lsa that it will not chop nearly as hard as the 110lsa of the SNS Stage 2. Let's take a closer look at how much overlap this cam actually has.
To determine overlap we add the intake and exhaust durations together and then divide them by two. This gives us 243. We now take the LSA and multiply it by 2 this gives us 232. Now subtract 243-232 = 11 degrees of overlap. So this camshaft has just as much overlap as the SNS Stage 2 with a 110lsa.
If you had the SNS Stage 2 cam installed in your car and replaced it with the 235/251 116lsa cam it would sound 100% identical to the SNS camshaft that you previously had installed. Again, LSA is just a sum of numbers and it doesn't matter!
I will leave this thread with one last suggestion. Do not pick a cam based on LSA. LSA is not the end all be all when it comes to camshaft performance or sound. Don't be lured into a trap by a manufacturer or a vendor when they tell you that, "X companies camshaft won't sound like you want it to because it's ground on a certain LSA". If you really want to know how two different camshafts will sound and want to see which one will chop harder at idle, just compare their overlap figures. If one has more overlap than the other it will chop harder than the other 95% of the time. If one has less overlap than the other it will chop less 95% of the time. Different exhaust systems and tuning can and will affect this, but for the most part overlap is a very good way in determining cam sound AND how drivable a camshaft will be. Don't think that just because a cam is ground on a tight LSA that it will be a pain to drive or because it's ground on a wide LSA that it will be a dream to drive.
I hope I have now instilled in those of you that read this that camshafts are just a sum of numbers. There are no absolutes in cam grinding. Everything is a compromise and not everything is as it seems at face value. Look deeper into your cam selections and compare valve events, overlap figures and not just duration and LSA specs. Compare the known performance of other camshafts with similar overlap and valve events to the cam you're considering purchasing. This will give much more insight into what you're looking for rather than just basing an assumption of LSA and duration.
I know that some of you already may know what I have put here, and that some of you may find this boring and not intriguing. For those that did not know this information I hope that after reading this thread you are better informed about your future or past purchases and are better informed into the how and the why cams do what they do.
AMEN Brother!
07-25-2014, 08:09 AM
#33
Aug 8th, 13, 9:32 AM
cstraub cstraub is online now
Join Date: Dec 2005
Location: Tri-Cities
Posts: 6,061
Default LSA, it is what it is...as it is a sum of numbers..
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My customer in NY that posted his dyno sheet and feed back from the CSC Legend cams have brought this post on.
LSA is really a sum of numbers that in the end, it is what it is. The engine, the rpm, the induction, and the exhaust need a "schedule". This schedule is valve events. This is what is critical, when you start and when you stop. The cid and rpm will put the demands on the engine and power range will determine where and the induction and exhaust supply the how.
For years I have have heard wide lobe sep for good vacuum. Well how about properly cammed engine for the intended rpm range and if the LSA is a 107 then thats what it is. I've got several of you on here and many others with vacuum reports of 11 to 15 inches during idle. These are customers wanting street cars with pop. These are not drag cars. Many circle track sanctioning bodies have Vac rules. Some pull truck stuff also. I have learned over the years manipulating the valve events you can achieve vacuum. These cams aren't on 112 or 114 LSAs I can assure you.
I re-cammed a 632CID engine for a gentleman in Denmark. The post is in my sponsors section. We went from a 256/269 .050" 708/720ish lift cam on a 115 to 253/269 .050" (note not much change at .050") 710/680" lift (again not much change) on a 107 Sep. The car is now just about as fast with the new cam NA as it was with the old cam and a 250 shot. No dyno numbers but just track time, but this had to have been a 150HP increase with cam change. The major change, LSA.
It has taken me years to figure some of this stuff out and I know the publlic is not going to change overnight. All I am wanting to get through to you, the board, that you can skin a cat several ways.
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Location: Tri-Cities
Posts: 6,061
Default LSA, it is what it is...as it is a sum of numbers..
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My customer in NY that posted his dyno sheet and feed back from the CSC Legend cams have brought this post on.
LSA is really a sum of numbers that in the end, it is what it is. The engine, the rpm, the induction, and the exhaust need a "schedule". This schedule is valve events. This is what is critical, when you start and when you stop. The cid and rpm will put the demands on the engine and power range will determine where and the induction and exhaust supply the how.
For years I have have heard wide lobe sep for good vacuum. Well how about properly cammed engine for the intended rpm range and if the LSA is a 107 then thats what it is. I've got several of you on here and many others with vacuum reports of 11 to 15 inches during idle. These are customers wanting street cars with pop. These are not drag cars. Many circle track sanctioning bodies have Vac rules. Some pull truck stuff also. I have learned over the years manipulating the valve events you can achieve vacuum. These cams aren't on 112 or 114 LSAs I can assure you.
I re-cammed a 632CID engine for a gentleman in Denmark. The post is in my sponsors section. We went from a 256/269 .050" 708/720ish lift cam on a 115 to 253/269 .050" (note not much change at .050") 710/680" lift (again not much change) on a 107 Sep. The car is now just about as fast with the new cam NA as it was with the old cam and a 250 shot. No dyno numbers but just track time, but this had to have been a 150HP increase with cam change. The major change, LSA.
It has taken me years to figure some of this stuff out and I know the publlic is not going to change overnight. All I am wanting to get through to you, the board, that you can skin a cat several ways.
07-25-2014, 08:19 AM
#34
Here is an example of two cams with the same LSA but different duration:
230/230 110+2
IVO is 7.0 ° BTDC ( - indicates ATDC)
IVC is 43.0 ° ABDC
EVO is 47.0 ° ATDC ( - indicates BTDC)
EVC is 3.0 ° BBDC
Overlap is 10 °
240/240 110+2
IVO is 12.0 ° BTDC ( - indicates ATDC)
IVC is 48.0 ° ABDC
EVO is 52.0 ° ATDC ( - indicates BTDC)
EVC is 8.0 ° BBDC
Overlap is 20 °
In this example a 10 degree increase in duration has doubled the overlap. You can imagine the difference in idle characteristics between these two cams. In order to get the 240 duration cam to have the same overlap as the 230 duration cam, the LSA would need to be widened to 115 degrees.
Conversely, if you were to look at IVO and the EVC above, you can quickly see the overlap increase. In fact, you can know the overlap with just those two events and do not even need to know duration, intake centerline or how much advance. But the cool part is that when I look at the individual events I can start to visualize what each of them does in a running engine and imagine how changes to individual events affect performance and that's when this really gets fascinating.
Last edited by speedtigger; 07-25-2014 at 09:10 AM.
07-25-2014, 09:22 AM
#35
I knew you would like this thread Chris!
Steve,
It really is cool to see you using valve events now instead of duration and LSA. I remember speaking with you a while back possibly a year or more ago and you having a slightly different outlook on all of this.
I like seeing how you've opened up to looking at the events and that you now see the big picture because of it.
Getting people to use what's in between their ears more and understand the physics of a running engine is the ultimate epiphany in engine building. If you can't grasp physics you cannot grasp the dynamics of a running engine.
I'm not saying that you have to be a physics major and have a masters in fluid dynamics or continuum mechanics, but an understanding will get you much further than most. A lot of engine building is common sense, but it still comes back to physics.
Wow. If anyone else would have told me this, I would have doubted them. That is tremendous. Where was the IVC on those two cams?
This is only true if the two camshafts are identical in duration. When the durations are not identical is where one can get the wrong impression about the overlap and performance characteristics.
Here is an example of two cams with the same LSA but different duration:
230/230 110+2
IVO is 7.0 ° BTDC ( - indicates ATDC)
IVC is 43.0 ° ABDC
EVO is 47.0 ° ATDC ( - indicates BTDC)
EVC is 3.0 ° BBDC
Overlap is 10 °
240/240 110+2
IVO is 12.0 ° BTDC ( - indicates ATDC)
IVC is 48.0 ° ABDC
EVO is 52.0 ° ATDC ( - indicates BTDC)
EVC is 8.0 ° BBDC
Overlap is 20 °
In this example a 10 degree increase in duration has doubled the overlap. You can imagine the difference in idle characteristics between these two cams. In order to get the 240 duration cam to have the same overlap as the 230 duration cam, the LSA would need to be widened to 115 degrees.
Conversely, if you were to look at IVO and the EVC above, you can quickly see the overlap increase. In fact, you can know the overlap with just those two events and do not even need to know duration, intake centerline or how much advance. But the cool part is that when I look at the individual events I can start to visualize what each of them does in a running engine and imagine how changes to individual events affect performance and that's when this really gets fascinating.
This is only true if the two camshafts are identical in duration. When the durations are not identical is where one can get the wrong impression about the overlap and performance characteristics.
Here is an example of two cams with the same LSA but different duration:
230/230 110+2
IVO is 7.0 ° BTDC ( - indicates ATDC)
IVC is 43.0 ° ABDC
EVO is 47.0 ° ATDC ( - indicates BTDC)
EVC is 3.0 ° BBDC
Overlap is 10 °
240/240 110+2
IVO is 12.0 ° BTDC ( - indicates ATDC)
IVC is 48.0 ° ABDC
EVO is 52.0 ° ATDC ( - indicates BTDC)
EVC is 8.0 ° BBDC
Overlap is 20 °
In this example a 10 degree increase in duration has doubled the overlap. You can imagine the difference in idle characteristics between these two cams. In order to get the 240 duration cam to have the same overlap as the 230 duration cam, the LSA would need to be widened to 115 degrees.
Conversely, if you were to look at IVO and the EVC above, you can quickly see the overlap increase. In fact, you can know the overlap with just those two events and do not even need to know duration, intake centerline or how much advance. But the cool part is that when I look at the individual events I can start to visualize what each of them does in a running engine and imagine how changes to individual events affect performance and that's when this really gets fascinating.
It really is cool to see you using valve events now instead of duration and LSA. I remember speaking with you a while back possibly a year or more ago and you having a slightly different outlook on all of this.
I like seeing how you've opened up to looking at the events and that you now see the big picture because of it.
Getting people to use what's in between their ears more and understand the physics of a running engine is the ultimate epiphany in engine building. If you can't grasp physics you cannot grasp the dynamics of a running engine.
I'm not saying that you have to be a physics major and have a masters in fluid dynamics or continuum mechanics, but an understanding will get you much further than most. A lot of engine building is common sense, but it still comes back to physics.
07-25-2014, 09:45 AM
#36
Steve,
It really is cool to see you using valve events now instead of duration and LSA. I remember speaking with you a while back possibly a year or more ago and you having a slightly different outlook on all of this.
I like seeing how you've opened up to looking at the events and that you now see the big picture because of it.
It really is cool to see you using valve events now instead of duration and LSA. I remember speaking with you a while back possibly a year or more ago and you having a slightly different outlook on all of this.
I like seeing how you've opened up to looking at the events and that you now see the big picture because of it.
08-02-2014, 02:29 PM
#39
Once you have determined the camshafts overlap period in cam degrees you can compare it to other camshafts that you may of been recommended to purchase. Or that you like the performance of.
This is the simplest way to get a feel for sound.
08-07-2014, 06:41 PM
#40
I don't understand how to come up with ICL and ECL. Are you taking LSA and applying any applicable advance/retard and that ends up being the ICL/ECL?
The first cam you mention, I imagine that would be sold as a 110+3 LSA cam correct?
so if I had a 110+2LSA cam, I would have 108/112 ICL/ECL?
The first cam you mention, I imagine that would be sold as a 110+3 LSA cam correct?
so if I had a 110+2LSA cam, I would have 108/112 ICL/ECL?