Cam Basics *

[MomsR/T]

Okay.......so my nitrous artical didn't make sticky staus nor get adopted in the KB section......but I want to thank the MODs for giving this artical (CAM-101) its proper place.

This by no means will make you a cam grinder, rather just allow many to understand cam basics..........

This will be long and so I will add to this ORIGINAL from time to time........if it gets too detailed I will make a CAM-201. :mrgreen:

I. Cam specs

a. Lift - Lift denotes the distance the cam will lift the valve off of the seat. Cam lift specs, however, may differ due to lift losses thru geometry and slippage. So therefor a cam with a .500 lift (said to have a 500 lift) is designed to lift the valve half an inch off of its seat. Once the engine is mocked up, you may find you actually receive only a .497 lift......this is okay.

b. Duration - Denotes the time a valve is left open.........duration numbers are often misunderstood and can be expressed many different ways. I will amend this section later to classify the math as to each way. I, and many others, look at duration at .05; this conveys to us the curve rate that can be graphed.

1. Duration can also be expressed as "advertised duration"....this number is used wrecklessly by aftermarket cam makers and can not be reworked to make any mathematical sense........."advertised duration" should not be used.

2. Duration may also be expressed at different points along the lift to denote the cams profile......how fast it peaks and how fast it falls. We'll discuss later how this all plays out and the math behind it, but by knowing one point and the cam's "events" you can figure for the duration curve.

c. LSA - Lobe seperation is expressed in degrees. (The cam has 360 degrees) This seperation gives you an idea of how long both the intake and exhaust valves are closed at the same time. The bigger the number the longer both valves are closed........the more cyl pressure is created.

d. Centerline / Overlap - Expresses the center point between the center of the intake vavle and the center of the exhaust valve...........during CAM-101 we will not discuss centerline at all. The full area of these 2 degree number (between the intake and exhaust valves) is known as Overlap.

II Engine Basics

In another post I was trying to express how the air is coming into the intake, thru the head, into the cyl, exploded, then exhausted.....

Please remember that the engine is alot like your computer "HARDWARE" while the cam is like it's program "SOFTWARE".

I also feel a need to explain a basic and rather crude rule; Air Mass = Horsepower while Air Speed / Velocity = Torque.

So, you would like to have a ton of air coming in and out of the motor right? It means you have a massive amount of horsepower right?

Well........sort of..........lets look at a practical exercise and see if this makes sense.

A garden hose @ 20' with 20psi of water pressure makes water come out of the hose and produces an arc than spans 6' when the hose is held at your waste.........if you hold your thumb of the hose end about half way it now shoots out 12'; but at a slight loss of total volume thru restriction.

If we were to take this same 20' hose however and tapered it ever-so slightly over the 20'......say 2" inner diameter at the faucet.........1.75" after 10' and 1.5" after the full 20', then the water might still spray out 12' but at a less restriction than our thumb given the same water pressure.

This would be torque!

If we were to take that same 20 psi from our house faucet and tried to run that thru a fireman's hose that is 6-8" in diameter.......we would be lucky if the water just dribbled out the end.........

So torque and horsepower can be at odds...............

This is also a good time to teach you what these terms mean. What the hell is horsepower anyways? Well.........its an obscure term kinda like slugging percentage is in baseball. Here is the equation.......

hp = trq x rpm / 5252

This shows us that hp is an abstract corralation between how much torque we have and where we have it............this is one reason why you can have 2 x 300hp cars and one feels fast while the other feels like a pig.

That strange 5252 number simply means that no matter how much power you make, for some strange reason, hp and trq always cross at that magic point.

So.......now we understand we need to make fast moving air but without choking the flow off so much we cut into out hp numbers.

****ie........too big of a port job on your head can make you run slower; it killed the velocity of the air so much that it was more of a trickle vs a sprayer (see hose stroy above).

Given the idea that our throttle body is big, it tapers down in size as the air comes into the intake, tapers more as it enters the intake runner in the head..........NOW WE NEED TO THINK ABOUT WHAT WE WANT TO DO?!?!?!

III Lift

So.....we have fast moving air that has made this long path all the way from the TB and now is sitting on the backside of our valve just waiting to enter the chamber.........depending on the AMOUNT of air and its VELOCITY will tell us how far to open said valve. If we open it too much we can actually slow this air-charge down........if we open it too little we will leave some power "on the table". Lets look at a practical exercise see we can better illustrate this effect:

********ie. We blow up the typical kids balloon......horse power would be the volume (gross amount) but remember that the torque will be the velocity (air speed). Given this, how big do we want to make the opening of this balloon so it flys around the room after we let it go?

If we make the opening too small it won't fly too fast; at extremes, it could just sit there and leak (like a small pin hole) while if its too big it too will just sit there and dump its air and not fly either. As we close in towards the middle from either extreme, somewhere in the middle we should find our purfect orface size of said balloon. THIS IS LIFT!

We won't go into hardcore physics, but try to understand the the shape of a valve is what it is to allow the air to rush 360 degrees around it and into the cyl chamber. This air path makes a HEMI work so well because there is room for the air to flow, with out turbulance, equally around the shape of this "pocket". A WEDGE styled head (most motor styles) always has 1 side of the intake valve covered up with the wall of said pocket.........that is to say "its up against the wall". This is refered to a SCHROUDING the valve........or covering up the valve. This is absolutely HORRIBLE! While one side of the valve can flow towards the center of the cumbustion chamber, the other side has HORRIBLE turbulance........this rolling-swirl will end up effecting our other smooth air while backing up the intake runner as long as its open......this will effect torque AND horsepower.

Head porters refer to fixing this problem by "UNSCHROUDING THE VALVE" by opening up that pocket and allowing that air to freely come out that side of the valve and curve around towards the center of the combustion chamber..........they also shape the chamber in the "heart shape" to promote this swirl.

We have no need for this due to our shape......HEMI, or actually, half a circle. So we can use lift and not be concerned with in-chamber turbulance from a schrouded valve.

So.........too much lift = slowing air speed while too little and we lessen our ability to make power.

We need to take a look at our head's flow chart to see what we have to work with. I will use HEAT's numbers as an example ONLY;

INTAKE SIDE FOR CNC PORTED 5.7 HEAD

200 LIFT = 148 CFM
300 LIFT = 233 CFM
400 LIFT = 285 CFM
500 LIFT = 308 CFM
600 LIFT = 318 CFM

I clipped off lift after .600 (6/10 of an inch of the valve off it's seat) because the heads no longer delivered flow after that. By reading these numbers we can see what these heads will flow and where they flow at. This chart shows us how much "cubic feet per minute" these heads will flow with the valve lifting this much..........

A valve lifting ANY further than the .600 lift mark could not deliver not one more ounce of horse power no matter what........the head design just will not allow any more air (water) to pass thru it per minute (@ 28" of water).

What this also shows us, mathematicly is where you really start to pick up flow........note the spread between 200 to 300 and 300 to 400......this tapers off at 500 and there is little gain up to the 600 mark. What this tells us is that our best VOLUME (see horse power) will be best realized with a total lift somewhere between the 500 and 600. For peak numbers (hp), we would lean towards the 600 mark while for lower end torque numbers we would lean towards the 500 mark. The closer we get to the 600 mark, the more we run a chance of becoming that balloon with a slightly too large opening.....

So lets look at the exhaust side and see if this is liniar.........

EXHAUST SIDE
200 LIFT = 96 CFM
300 LIFT = 147 CFM
400 LIFT = 183 CFM
500 LIFT = 207 CFM
600 LIFT = 213 CFM

I clipped off lift after .600 (6/10 of an inch of the valve off it's seat) because the heads no longer delivered flow after that; just like above. Do you still notice how the gains from 200 to 400 are dramatic but we start to slow after this?

Its good that we see liniar trends, this means we can make a cam that will also is liniar..........total lift between 500 and 600; closer to 500 for torque with closer to 600 for top end horsepower.

******NOTE - Remember when I said you want to taper the air? With ported heads, we also need to note how our intake flows coming to these heads.......if the intake is too small, these lift numbers (flow) will never be achieved while if our intake is too big, the air will tend to "mill-about" or "hang-out" in there versus directly speeding towards a given path. We also would like to see a clean transition from intake to head........if our intake is properly matched to the head, then we can get properly size our cam.

THE PLASTIC 5.7 INTAKE FLOWS SMOOTH, DISPERSES HEAT NICELY AND IS SIZED WELL FOR THIS PORT SHOWN ABOVE.

There will be no MAGIC number I can give you for the "perfect" 5.7 cam in regards to lift..........it depends on the application and every small variable I can't prepare for. But now being able to understand a head-flow-chart and see how it relates to cam selection, you too can start to move in the right direction; this clearly shows however, that a ported head with the stock 5.7 cam-shaft is leaving a boat-load of power on the table!

[CoolVanilla]

To the KB this goes.

Should be required reading for the beginning modder. Thanks MRT!

[Ozzie]

Jeeezz! Even I can understand it! Outstanding job. Keep 'em coming.

[MomsR/T]

Thanks.......like I said.........this will be basic.

Once I can get everyone understanding the numbers on a cam-sheet and what those mean AND what we are trying to accomplish, then we will try and predict what certain cam specs will do.........

It will be theoretical..............but its not bench racing rather trying to predict what cam will behave like you want it to.

This way, as we now have more and more heads and cams coming out, you guys can be your own bosses and make practical choices.........."Don't give a man a fish....rather teach him how to fish......"

After I finish the artical, I'll let it linger so we can banter the facts and make sure those interested have the time to soak it in.......

I would like you guys doing the MoFo to play the guessing game and try to look at the cams going into these cars and predict where the curves will be based upon your educated guesses...........you'll scare yourself how right you are.

I hope you all then return with your results and tell us how this "class" was............

[MomsR/T]

IV Duration

I will keep it as simple as possible without being to vague.........duration is expressed in one of two ways; advertised (the B.S. way) and / or at a given lift (the proper way).

Duration has got to be the hardest expression of a cam design to explain.......this may require you read this portion a couple/few times to soak it in.......and if you want to be able to review this stuff again I suggest you take notes.

Advertised Duration

Advertised duration is a relative term that may vary from one manufacturer to another. These companies use computer programs to design profiles. The computer then uses duration at lifts from 0 - .025....... however they are not consistant; different manufacturers use different standards and lift numbers.

The computer then creates a lift-table then calculates the rate at which that line progresses........"an escallating line". The cam programmer is looking for a time he / she would like to keep said valve open in relation to "*events*".

(Events - are expressed as the the intake opening / closing and the exhaust opening and closing in degrees...............these 4 numbers are refered to as the four EVENTS)

So if your lost......its okay I'll try and make it a little easier.

A computer geek who knows how a motor works is sitting behind a computer and looking at a graph. Next to it, he has certain perameters of a given motor. With those given perameters, he is looking for how long he wants to flow air, at any given point, as it relates to the 4 events.

As he graphs this on his computer, the computer will allow him to drag the curve back and forth till he gets it right. Once it looks the way he wants it, the computer will see 2 individual "camel humps" on the graph. One hump is the intake and the other is the exhaust..........these humps are the LIFT NUMBERS..........the angle in which they climb will be mathematicly figured by the program and thus it produces and ADVERTISED DURATION.

Depending on who and how this program was designed, it may figure advertised duration from 0 lift + x = rate of lift or it may used .025 + x = rate of lift. WHO THE HELL KNOWS!?!?!?!

This is no way to figure anything out on a cam.........its vague and unless you work for that particular cam company and know how to decode the figure then it's worthless.

Duration @ a Given Lift

This will be the most suck-ass thing to explain........if you are reading this and have made it this far, go get a life and give up cars while you can! Cars will make you poor, pissed off, and produce head aches most medicines can't cure!

Okay......if you're still with me then get out your pencil........

Just like when we discussed lift, I will select the intake valve to harp on; but also like lift, anything thats true for the intake vavle will be true for the exhaust valve.

(If you have never seen a cam this will be more difficult for you to imagine...........please seek one out then re-read this for clairification.)

As we look at a cam, we see its a long shaft......kinda like the center, cardboard roll inside a roll of paper towels. But upon further inspection we see it has a bunch of lobes on it (16 - 8 intakes and 8 exhaust). These lobes have the shape of eggs.........and like an egg, as we roll them, they have a distinct pattern of low low low then HIIIIIGH point. You roll the egg again and you see it roll low low low and HIIIGH point.

The time that this egg rolls across your table, you will see that it slows down ALOT as it takes that high point turn. The duration that we are seeking is "how do we express the time it takes to go over that peak".

Auuuuuuhhhhhh.........I see the light going off in your head right now! (understanding the concept is half the battle)

Using a degree wheel, we need to take some readings so we can figure duration for a cam if its unknown. We will take the sum of the intake lobe's opening degree, plus the sum of the intake lobe's closing degree, plus 180. We must add 180 because the crank will make 2 rotations for every one the cam makes.

Therefor if the intake valve starts to move @ 30 degrees BEFORE TOP DEAD CENTER (BTDC) and stops moving (closes) at 50 degrees AFTER TOP DEAD CENTER (ATDC) then the duration would be 260 degrees. (Intake Duration = IO + IC + 180).

We express this the same way for exhaust...........there could be issues depending on events but lets just keep it simple for CAM-101 shall we?

Now listen..........we know the duration is 260. If we were to make a graph a show the hump we just plotted, we can now figure for lift at different lift points..........

The bottom of this graph would show degrees with the events noted........then we would plot at what point our lift is achieved..........the width of the bottom of this triangle (hump) is 260 degrees wide.

The left side of this graph would show lift..........0.100, 0.200, 0.300 and so on. So we know how high it goes and we know how wide it is.........now, on ANY given point (lift) on this graph we can plot for duration.

The common point at which to express duration is at 0.050...........the reason for this is because as we get closer to the top of this triangle (hump) the numbers become smaller (0.100 lift duration is more than 0.200 lift duration because you are traveling up the curve). The larger number seemed to have been more clear to people in the past and its just stuck for all these years.

One day I will work with someone that knows how to make graphs and I will express this so you can actually see it. In CAM-201 I will work with someone to show how to use the degree wheel with a dial indicator and you will see how we got these numbers and degrees.


V LSA

Lobe seperation was defined above. While LSA is clearly a bi-product of the cam's design, we can manipulate this number in our design so that we can either broaden our torque curve or narrow our torque curve..........Why would we want to do that? Glad you asked.......

Take drag racing........a great American past-time that is as much apart of this nation as baseball, apple-pie, and Colt .45's. In drag racing you want to reach 1/4 mile as fast as possible..........one way to do that is to launch your car right before its peak torque (getting the car out of the hole as fast as possible). So if we are shifting at 6500 and make peak torque at 4800, we would consider leaving the hole at around 4200 (flashing to 4600).

Well lets think about that.......we are sitting in the staging lanes waiting for a green light with the needle of our tach touching the 4200 RPM line (WOW).

So, our car will NEVER need to make ANY power from 1000 RPM to 4000 RPM...........we don't need air velocity there, we don't need drivability there....NOTHING! All of our flow and speed numbers will be directed to that sweet spot between 4200 - 6500.

With this narrow RPM band, we can get more power out of our cam spec by lowering the LSA............HOWEVER, we should expect that as our power increases it will also move further up the RPM line. I'll give an example:

******ie. Two cams with the exact same specs in regards to lift and duration; the only change being LSA. We will call the larger LSA cam, CAM A and the cam with the smaller LSA we will call CAM B.

CAM A will have a broader torque curve.........making power at low RPM's and carring all the way till the end while CAM B will suffer at the low RPM's but show considerable gains in the middle then tapers off quick at the end. If CAM A were to achieve peak torque @ 3400 RPM, the smaller LSA-ed CAM B might show a peak torque @ around 4400 (as an example ONLY).

So our first car that we were speaking of, the drag car that leaves the line at 4200 RPM doesn't need that low RPM torque curve does it? Nope! It needs power in a very specific place and ONLY there.......it also only needs power for a short time. The small LSA allows this car to stay in its sweet spot while making the MOST power.

******NOTE - If you want to imagine what LSA does......go outside and break off a small, green twig. Hold it chest high, centered on your chest. Compress this green-stick with your hands SLIGHTLY! Examine the slight bow in this stick but also note that it still remains almost as long.........this is a high LSA.

Now compress this stick twice as much...........note that the bow is now very large, BUT its very very short. This is a low LSA...............

Application

For a street car that lives the majority of its life from idle to 2,000 rpm, a larger LSA is recommended. You can tighten it up slightly to make more power, but more isn't better. The stock 5.7 is a 117 LSA...........by talking to folks with aftermarket or non-stock cams, you should be able to look at their dyno graphs to see the mid-rpm gains and equate some of that not only to lift and duration numbers but also to LSA.

As the LSA drop numericly, remember it also slides the peak towards the upper RPM's...........

I suspect that we will see the majority of these high performance street cars will find the 115 - 114 LSA to have the best driveability with the best power COMPRIMISE........(key word).




VI Centerline / Overlap

(taking a break.........my head hurts!)

[MadCharger]

Where's the video????

Great job Moms - now I know that I need to return that .710/.700 cam I bought on Ebay....... ;)

[MomsR/T]

Where's the video????



Bite me! :blam:

I had to take asprin my mind was working so much.....I had to selectively leave out stuff just to TRY and not make this worse than it already is!

Can you make anything out of this?

If you didn't know ANYTHING......is this okay?

[MattRobertson]

If you didn't know ANYTHING......is this okay?I will let you know as I am that guy. Mucho kudos, green beans and thanks as I've been muttering to myself for months on this subject.

[rander]

Yeah, really good job!!! there r/t. I'm more motivated than ever!

[RTracer]

Incredibly informative write up:thumbs_u:

I remember years ago, my buddies and I figuring out the equalibrium point on the HP/TQ curve...we were perplexed

[MadCharger]

Can you make anything out of this?

If you didn't know ANYTHING......is this okay?

This was a great recap of much of the stuff you explained to me on the phone - and since I only retain about 2% of everything I hear, this makes it easy to read again if I forget....
Great job!

[MomsR/T]

MOD.......

Please move POST #5 under POST #1 so it may be read continous for best results........ty. :thumbs_u:

If this is not possible, please delete your post and Ozzies so we can accomplish the same thing........

This weekend I am busy busy busy......but I will finsh the last paragraph ASAP on Overlap.

Instead of taking a butt load of pictures, I am considering going thru all of my books and using pictures from them to show what I was talking about.............graphs, tools, cams, and even a green-stick :wink:

Thanks for the support from the MODs and the fellow LX community.

[BMDMC]

Very nice newby explaination, but where are the graphs? Every cam made has a purpose but the big question is what's right for a specifc application. Lets say I want to replace the CAMs in my stock SRT8, what should I use?

IV Duration

I will keep it as simple as possible without being to vague.........duration is expressed in one of two ways; advertised (the B.S. way) and / or at a given lift (the proper way).

Duration has got to be the hardest expression of a cam design to explain.......this may require you read this portion a couple/few times to soak it in.......and if you want to be able to review this stuff again I suggest you take notes.

Advertised Duration

Advertised duration is a relative term that may vary from one manufacturer to another. These companies use computer programs to design profiles. The computer then uses duration at lifts from 0 - .025....... however they are not consistant; different manufacturers use different standards and lift numbers.

The computer then creates a lift-table then calculates the rate at which that line progresses........"an escallating line". The cam programmer is looking for a time he / she would like to keep said valve open in relation to "*events*".

(Events - are expressed as the the intake opening / closing and the exhaust opening and closing in degrees...............these 4 numbers are refered to as the four EVENTS)

So if your lost......its okay I'll try and make it a little easier.

A computer geek who knows how a motor works is sitting behind a computer and looking at a graph. Next to it, he has certain perameters of a given motor. With those given perameters, he is looking for how long he wants to flow air, at any given point, as it relates to the 4 events.

As he graphs this on his computer, the computer will allow him to drag the curve back and forth till he gets it right. Once it looks the way he wants it, the computer will see 2 individual "camel humps" on the graph. One hump is the intake and the other is the exhaust..........these humps are the LIFT NUMBERS..........the angle in which they climb will be mathematicly figured by the program and thus it produces and ADVERTISED DURATION.

Depending on who and how this program was designed, it may figure advertised duration from 0 lift + x = rate of lift or it may used .025 + x = rate of lift. WHO THE HELL KNOWS!?!?!?!

This is no way to figure anything out on a cam.........its vague and unless you work for that particular cam company and know how to decode the figure then it's worthless.

Duration @ a Given Lift

This will be the most suck-ass thing to explain........if you are reading this and have made it this far, go get a life and give up cars while you can! Cars will make you poor, pissed off, and produce head aches most medicines can't cure!

Okay......if you're still with me then get out your pencil........

Just like when we discussed lift, I will select the intake valve to harp on; but also like lift, anything thats true for the intake vavle will be true for the exhaust valve.

(If you have never seen a cam this will be more difficult for you to imagine...........please seek one out then re-read this for clairification.)

As we look at a cam, we see its a long shaft......kinda like the center, cardboard roll inside a roll of paper towels. But upon further inspection we see it has a bunch of lobes on it (16 - 8 intakes and 8 exhaust). These lobes have the shape of eggs.........and like an egg, as we roll them, they have a distinct pattern of low low low then HIIIIIGH point. You roll the egg again and you see it roll low low low and HIIIGH point.

The time that this egg rolls across your table, you will see that it slows down ALOT as it takes that high point turn. The duration that we are seeking is "how do we express the time it takes to go over that peak".

Auuuuuuhhhhhh.........I see the light going off in your head right now! (understanding the concept is half the battle)

Using a degree wheel, we need to take some readings so we can figure duration for a cam if its unknown. We will take the sum of the intake lobe's opening degree, plus the sum of the intake lobe's closing degree, plus 180. We must add 180 because the crank will make 2 rotations for every one the cam makes.

Therefor if the intake valve starts to move @ 30 degrees BEFORE TOP DEAD CENTER (BTDC) and stops moving (closes) at 50 degrees AFTER TOP DEAD CENTER (ATDC) then the duration would be 260 degrees. (Intake Duration = IO + IC + 180).

We express this the same way for exhaust...........there could be issues depending on events but lets just keep it simple for CAM-101 shall we?

Now listen..........we know the duration is 260. If we were to make a graph a show the hump we just plotted, we can now figure for lift at different lift points..........

The bottom of this graph would show degrees with the events noted........then we would plot at what point our lift is achieved..........the width of the bottom of this triangle (hump) is 260 degrees wide.

The left side of this graph would show lift..........0.100, 0.200, 0.300 and so on. So we know how high it goes and we know how wide it is.........now, on ANY given point (lift) on this graph we can plot for duration.

The common point at which to express duration is at 0.050...........the reason for this is because as we get closer to the top of this triangle (hump) the numbers become smaller (0.100 lift duration is more than 0.200 lift duration because you are traveling up the curve). The larger number seemed to have been more clear to people in the past and its just stuck for all these years.

One day I will work with someone that knows how to make graphs and I will express this so you can actually see it. In CAM-201 I will work with someone to show how to use the degree wheel with a dial indicator and you will see how we got these numbers and degrees.


V LSA

Lobe seperation was defined above. While LSA is clearly a bi-product of the cam's design, we can manipulate this number in our design so that we can either broaden our torque curve or narrow our torque curve..........Why would we want to do that? Glad you asked.......

Take drag racing........a great American past-time that is as much apart of this nation as baseball, apple-pie, and Colt .45's. In drag racing you want to reach 1/4 mile as fast as possible..........one way to do that is to launch your car right before its peak torque (getting the car out of the hole as fast as possible). So if we are shifting at 6500 and make peak torque at 4800, we would consider leaving the hole at around 4200 (flashing to 4600).

Well lets think about that.......we are sitting in the staging lanes waiting for a green light with the needle of our tach touching the 4200 RPM line (WOW).

So, our car will NEVER need to make ANY power from 1000 RPM to 4000 RPM...........we don't need air velocity there, we don't need drivability there....NOTHING! All of our flow and speed numbers will be directed to that sweet spot between 4200 - 6500.

With this narrow RPM band, we can get more power out of our cam spec by lowering the LSA............HOWEVER, we should expect that as our power increases it will also move further up the RPM line. I'll give an example:

******ie. Two cams with the exact same specs in regards to lift and duration; the only change being LSA. We will call the larger LSA cam, CAM A and the cam with the smaller LSA we will call CAM B.

CAM A will have a broader torque curve.........making power at low RPM's and carring all the way till the end while CAM B will suffer at the low RPM's but show considerable gains in the middle then tapers off quick at the end. If CAM A were to achieve peak torque @ 3400 RPM, the smaller LSA-ed CAM B might show a peak torque @ around 4400 (as an example ONLY).

So our first car that we were speaking of, the drag car that leaves the line at 4200 RPM doesn't need that low RPM torque curve does it? Nope! It needs power in a very specific place and ONLY there.......it also only needs power for a short time. The small LSA allows this car to stay in its sweet spot while making the MOST power.

******NOTE - If you want to imagine what LSA does......go outside and break off a small, green twig. Hold it chest high, centered on your chest. Compress this green-stick with your hands SLIGHTLY! Examine the slight bow in this stick but also note that it still remains almost as long.........this is a high LSA.

Now compress this stick twice as much...........note that the bow is now very large, BUT its very very short. This is a low LSA...............

Application

For a street car that lives the majority of its life from idle to 2,000 rpm, a larger LSA is recommended. You can tighten it up slightly to make more power, but more isn't better. The stock 5.7 is a 117 LSA...........by talking to folks with aftermarket or non-stock cams, you should be able to look at their dyno graphs to see the mid-rpm gains and equate some of that not only to lift and duration numbers but also to LSA.

As the LSA drop numericly, remember it also slides the peak towards the upper RPM's...........

I suspect that we will see the majority of these high performance street cars will find the 115 - 114 LSA to have the best driveability with the best power COMPRIMISE........(key word).




VI Centerline / Overlap

(taking a break.........my head hurts!)

[MomsR/T]

graphs eh.........

one day............graphs take time, something I'm short of.

As for now, if you would like a I would suggest talking to someone like HEAT Performance who makes cams for specific needs........there is no "one cam for any one car" rather a bunch that will do the job depending on combination and expectations.

All I was trying to do was give VERY basic ideas to people that have no clue to what the rest of us are talking about.

[Mr. Squiggles]

Hey Moms! Did that headache finally go away? I'd be interested in reading the 'final chapters' on this.

[STAGE 3 R/T]

Great write up! My brain hurts now...

[stevesrt8]

thanks for reducing that "cam tech" to easily understood terms!

Educating your customers always helps them!

[monty1269]

:bump:

Since there are SO many cams being installed lately... I think this thread deserves a BUMP!

[iceman-5076Hemi]

WOW!!!! just came across this. Before reading this article it was kinda like when you were in the 9th grade, sitting around the lunch table and you always had one or two of the guys talking about sex b/c they actually did it and everyone else lied and shook their head in agreement like they knew what in the hell the other guys were talking about...now I feel like one of those guys that actually did it!!!!!!:shock: I need a cigarette now...and nap!!!

Beans to ya! bookmarked for future brain farts.

[tmac06srt8]

Thanks for this!!!!!! This will gt me started on my search for the right cam for my srt8 with stock heads. Now I can talk to the vendor and know 10% of what he is talking about. Cheers!!!

[Nitecop]

I only joined recently. I know its a old thread. But a very good read. I particully like your explaination of Lobe Seperation Angle.
(I'm an former Crane Cam tech guy)

[351Freak]

Don't get hung up on "velocity"...

Just as a head may be considered "too big"...so can a camshaft...

The cylinder head is a RESTRICTION to the airflow...regardless of how much it flows...

Same goes for the intake...

You must size all three components properly to make an excellent combination.

If you do...the reward is a nice flat TQ curve.

You also don't want to forget about the 5th cycle to this 4-stroke motor...overlap and scavenge...

During a very brief moment of time (around TDC)...the exhaust can actually pull many times harder on the intake than the atmosphere can push...

Research "David Vizard" for some interesting reading on exhaust modeling.

and "Wighat" or Buddy Rawls for "cam truth" for a more advanced primer on cam design...

Huge heads can be made to work really well...but the margin for error becomes incredibly smaller.

Fords are notorious for this...but there are many folks that have successfully done it.

-Freak

[Rt's RT]

Awesome job! does anyone know the flow numbers on the stock 09 SRT heads?

[atwong1]

Great writeup. Now I can shop.