Sales@Tick

iTrader: (3)

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.

HCI2000SS

iTrader: (2)

Great info Martin!

Atomic

iTrader: (37)

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.

KrisR

iTrader: (2)

Awesome post Martin. This kind of thing is one of the reasons I ordered a camshaft from you.

Felix C

Goes counter to everything we have been taught since I started reading here in 2004.

I seem to recall a comment by SStrokerAce(sp?), a professional engine builder of long standing, regarding how important it is.

Fry_

It seems like the most know about custom cams the more I realize I don't know enough to spec one myself. Thank you for helping explain the process.

Sales@Tick

iTrader: (3)

LSA as a number itself does not matter.

When it comes to figuring valve overlap it does matter.

Bret is a good friend of mine and we have talked about this at length.

We both understand and both respect how we come to our own specifications. Bret uses duration and LSA, I use valve events.

To each their own. My post wasn't so much as to say to totally disregard it, but do not use it to select a camshaft based on performance or sound.

dr_whigham

iTrader: (49)

Thanks for spending the time to hammer this out for us folks, Martin. Perhaps this needs to be blue...

"MAC"

iTrader: (1)

Thanks Martin i feel like you have opened my eyes a bit on cam info. Great post no doubt.

Sales@Tick

iTrader: (3)

I would say the most common question I get while speaking with a customer is, "will this cam sound good at idle"?

I felt that this thread would address that and why sometimes people are misled to the way a cam should perform or sound based solely on its LSA.

The title of the thread and the statement that, "LSA doesn't matter" wasn't made to discount LSA 100%. It was was made to catch your attention and to break the myths that LSA controls the way a cam sounds or changes the performance of a camshaft.

It is really the changing of the lobe centers that accomplishes this, not the change in LSA.

That was my point I was trying to make.

I think it would be great if this was made a sticky!

KCS

iTrader: (20)

So if you were to pick 3 values in order to describe a camshaft to someone, would LSA be one of them? It seems like intake and exhaust duration and LSA are the three most common values used to describe a camshaft throughout the industry. If it isn't useful for performance or sound characteristics, why is it listed for all the cams you sell on Tick's website?

From the perspective of designing a camshaft, sure, the LSA is going to be whatever it's going to be, but when you're selecting a camshaft, I think the LSA is a pretty important piece of information...at least a top three.

Rise of the Phoenix

iTrader: (27)

Good information there Martin. You are a great asset to this forum and the LSx community as a whole.

Sales@Tick

iTrader: (3)

I would choose intake duration, exhaust duration and LSA only because those are the three most common identifiable specifications that the majority of enthusiasts can relate to.

If I started mentioning valve events to customers I can easily see how that would get confusing very quickly.

As I said in post number 10 my post was simply to open people's eyes that LSA is not the end all be all and it should not be used to choose a camshaft based on performance or sound. That the changing and manipulation of the lobe centers is what changes performance and sound when the LSA is widened or tightened. Not the actual change in LSA itself.

Blackpanther99

iTrader: (8)

Thanks for sharing Martin, thats why I went with you for my custom grind on my truck!

Sales@Tick

iTrader: (3)

No problem Alex.

"MAC"

iTrader: (1)

Please keep cam recommendations to PM or this thread.

http://www.ls1tech.com/forums/showth...799&styleid=27

99Bluz28

iTrader: (35)

Good thread Martin!
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.

"MAC"

iTrader: (1)

My bad who ever changed my statement

mchdg86

iTrader: (3)

I don't expect you to give your secrets away. But can you help me understand valve events and there affect on the power band?

Blackpanther99

iTrader: (8)

x2... Im also curious about the valve events.

Hooefully you can share, if not its cool since it could be a secret.