Originally Posted by Sales@Tick

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 al

so 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.

Originally Posted by vikingray

Originally Posted by Fbodyjunkie06

That's because the valve events changed. Wider LSA later IVC earlier EVO. Tighter LSA earlier IVC later EVO.

IMO Richard like many others attempts to simplify complex notions and tries to create generalities that then create confusion among those who are less educated on the subject.

Originally Posted by Fbodyjunkie06

That's because the valve events changed. Wider LSA later IVC earlier EVO. Tighter LSA earlier IVC later EVO.

IMO Richard like many others attempts to simplify complex notions and tries to create generalities that then create confusion among those who are less educated on the subject.

Originally Posted by LS1Formulation

I absolutely hated that article when I read it in Hot Rod. Why? Because the cams should have all been installed with the exact same ICL, to show what the actual effect of adding overlap to a given combo would do. No one ever seems to mention WHY overlap is beneficial in a NA performance application. As your exhaust is exiting through the headers, a negative pressure wave is produced that creates a vacuum on the cylinder just as the intake valve is opening. This allows the cylinder to fill more thoroughly than it could if only relying on atmospheric pressure. However, at lower RPMs, the exhaust velocity is not high enough to pull a vacuum on the cylinder, so some of the exhaust gets pushed back into the intake, diluting the intake charge and creating the "chop" that everyone loves.

Originally Posted by essamforlife

Too many give the LSA more importance than it's due, mainly from lack of understanding that it's only one of many pieces of the puzzle.