I clipped this from another thread.

"FYI, The intake centerline (ICL) is the LSA minus the amount of advance ground into the cam. So, your 228R has a 109 ICL and 112 LSA, so there's three degrees of advance."

Thanks!
Trevor

My cam card says "0" advance, 114 LSA 112 ICL. I am missing something? Shouldn't either the advance say "2", the LSA say 112, or the ICL say 114 ?


Serial # E 7542-05 Spec Card# 07791505
Part # 54-000-11 LS1 CHEVY LS1/GEN III '97-UP ROLLER
Core C54-11A LS1 1997 UP 5.7 CORVETTE 5150 SEMI
Grind # LS1 3724R/ 3727R HR14
DURATION @ .050 INTAKE 228 ROCKER ARM RATIO
VALVE ADJ INTAKE .000 DURATION @ .050 EXHAUST 234 INTAKE 1.70
VALVE ADJ EXHAUST .000 LOBE LIFT INTAKE .3460 EXHAUST 1.70
VALVE LIFT INTAKE .588 LOBE LIFT EXHAUST .3520
VALVE LIFT EXHAUST .598 LOBE SEPARATION 114.0
DURATION .006 INTAKE C/L 112.0
TAPPET LIFT INTAKE 277 CAM ADVANCE 0
TAPPET LIFT EXHAUST 283 HYDRAULIC Y
VALVE TIMING .050 OVERHEAD CAM N
VALVE OPEN INTAKE 2 JOURNAL DIAMETER STD 2.165
VALVE OPEN EXHAUST 53 RECOMMENDED VALVE SPRINGS
VALVE CLOSED INTAKE 46 DEPARTMENT P
VALVE CLOSED EXHAUST 1 SPC INSTR FOR CUSTOMER

 

Nobody has an idea????

 

ICL and LSA have nothing to do with each other. Most often the numbers might be the same but they are different references. ICL (intake center line) is the spot where the cam is matched dot to dot with the crank when the #1 piston is at Top Dead Center (TDC). LSA (Lobe Separation Angle) is just that, the number of degrees the peak of the intake lobe is from the peak of the exhaust lobe, it has nothing to do with the advance of the cam. Comp Cams usually grinds in an advance since most often 4 degrees advance shows the biggest HP gains, and hardly ever should you go more then 4 degrees max!!! If you do you really need to know what you're doing and how things work. Mine was ground in 3 degrees advance so my ICL is 112+3 and my LSA is 112. (again my ICL and LSA are the same but they have no reference to each other, I do still have 3 degrees advance ground in showed as the +3). Always go by your cam card, it says 0 degrees advance so your cam was ground directly on the Intake Center Line. Meaning it is up to you or your installer/shop to advance the cam if you so choose. The only plus to the advance ground in is that you pretty much just line up dot to dot and it's good. But if you don't know if there's an advance ground in or not, be extremely careful advancing your cam as going over the 4 degrees is dangerous and could destroy your valves and pistons, and potentially your heads and bores, crank, etc.

You do indeed have a 114 lobe seperation angle (LSA) and a 112 Intake Center Line (ICL) And you do in fact have 0 degrees advance ground in. So now find that guy in the other thread and tell him he's ignorant and shouldn't be giving advice until he finds his facts.

 

 

I did some more digging around

"- Subtracting the ICL from the LSA will give you the advance: 112 – 108 = 4 using the T1. Or 113 – 109 = 4 using the G5X2."


"Whats the LSA?
LSA - x = ICL
x = Cam advance"

This one from PredatorZ
"ICL = LSA- Advance in grind
If cam retarded (like 113-2)
then ICL is 113 - (-2) = 115 ICL"

PatrickG and Hammertime
"112 LSA +4 advance = 108 ICL"

RAACCR
"LSA = 112* (ICL+ECL)/2 = LSA
Your cam is ground with 5* advance
ICL = 107*
ECL = 117*"

YankeeVert
"ICL=LSA-advance=113-0=113"

I could dig up this equation a hundred times on this site. In my first post the quote was from Trevor at Texas Speed.

 

I put that thing in dot to dot, then degreed it. Ofcourse, it was off like normal. I set it up the IVO at 3*, and had it closing at 46*. I checked the PTV clearance an it was down to .083" on the intake, and .125 on the exhaust. I bumped the cam back to 1* IVO and that put the PTV clearance at .098". I really dont want to retard the cam, but my friend that builds motors says I wont really notice the difference. Would it be safe to run with the PTV clearance at .083" ?

 

.083 is plenty of PTV. With ported LPE LS6 heads with 2.02/1.57 valves milled to 62cc and a .052 MLS gasket, I have .056 I & .112 E PTV. This is with the LG G5X3 114 LSA camshaft.

Russ Kemp

 

Found on the Car Craft tech articles section.. should answer everyone's questions.

Intake Centerline

Now that you have lift and duration mastered, we can move on to more of the measurement values in camshaft design. Imagine looking at a lobe with a vertical line running right down the middle as viewed from the end. This line would represent the centerline of the lobe. If this were an intake valve, this would be the intake centerline of the lobe. Cam designers and engine builders use this centerline to establish where the lobe is located relative to the piston. For example, a Comp Cams 268 Xtreme Energy cam has an intake centerline of 106 degrees ATDC. This means that the midpoint of the lobe (which may or may not be maximum lift, since some cams are asymmetrical in design), will occur when the Number One piston is positioned at 106 degrees after top dead center.



When installing a camshaft in an engine, performance engine builders and the blueprinting process demand that you measure or "degree" the camshaft to ensure that it is installed where the engine builder desires. It's not enough to merely line up the dots on the cam and the crank gear. This way, if the engine builder would like to change the phasing of the camshaft, he can use that installed point as a reference. It's tough to know where to go if you don't know where you are.

This phasing of the camshaft is important because when the valves open and close has a serious effect on engine performance. This is where we get into advancing or retarding the position of the camshaft relative to the Number One piston. All references to positioning a cam are always around the intake lobe for the Number One cylinder. So if we wanted to advance the previously mentioned 268XE cam with its 106-degree intake centerline by 2 degrees, this would open the valve earlier in the cycle. It would place the intake centerline at 104 degrees after top dead center (ATDC).

Conversely, if we wanted to retard the camshaft by 2 degrees, this would move the original 106-degree centerline to 108 degrees ATDC. This is an important point that many people get backwards, so take a minute or so to study why these numbers are correct by looking at the cam timing graph.

Advancing the camshaft means that you are starting the opening and closing process sooner in the cycle. It generally improves low-speed torque and mid-range power while sacrificing top-end hp. Conversely, retarding the cam detracts from low- and mid-range power in order to help top-end power. Generally, moving a camshaft a couple of degrees will not make dramatic changes to the engine's power curve.



Lobe Separation Angle

Here's where we get into some meaty stuff, so stay with us. If you look at the lobe graph, you can see the relationship of the intake and exhaust lobes. One of the variables that make cam designing such a challenge is the relationship of the intake to the exhaust lobe. The number of degrees between the intake and exhaust lobe centerlines establishes what is called the lobe separation angle. As an example, many Crane street camshafts are built using a 112-degree lobe separation angle. This means there are 112 camshaft degrees between the exhaust and intake centerlines. This can be determined from a cam card by adding the exhaust and intake centerline numbers together and then dividing by 2. So if you add a 111-degree exhaust and a 113-degree intake lobe centers and divide by 2, you'd get a 112-degree lobe separation angle. Keep in mind that often the intake centerline and the lobe separation angle will be the same number, but they represent completely different functions.

Valve overlap is a function of both duration and lobe separation angle. If the lobe separation angle remains the same but you increase the duration, the amount of overlap will also increase. Overlap is the time, measured in crankshaft degrees, when the exhaust valve and intake valves are both open. Overlap helps improve engine performance by starting the intake cycle before the exhaust cycle has ended. As overlap increases, this tends to make the idle quality more erratic, or lumpy, while improving midrange and top-end power. This is a very complex subject that we'll just touch on here, but even slight changes in overlap and intake opening and closing points can make a big difference in engine performance.

 

I dont see anything in that write up that uses LSA ICL to determine ground in cam advance

 

Ok, I guess I am going with this. I suppose my cam card is fubar?????

"D. Advance and Retard:

- When you see cams specs like 224/224 .563/.563 112+4; the +4 denotes that the cam has 4 degrees of advance ground in.

- Most off the shelf cams have 2 or 4 degrees of advance ground in. This lowers the power band slightly and offers more low end and midrange at the sacrifice of a bit more top end power

- For cams used primarily on the street the advance is best appreciated. For a strip or racing setup 2 or 0 degrees advance will net you more peak power in the upper ranges of the power band

- To find out if you cam has advance ground in you can check on the cam card. Besides the +2, +4, you can determine the number by looking at the intake center line (ICL). Referring back to the T1 cam card you’ll see that it states that those are the specs when installed on a 108 ICL.

- Subtracting the ICL from the LSA will give you the advance: 112 – 108 = 4 using the T1. Or 113 – 109 = 4 using the G5X2.

- Retarding the cam does the opposite of advancing it, it pushes the power band up slightly and gives more top end power.

- With an adjustable timing chain or degreeing the cam you can install the cam at different ICL’s. "

I found this bit in the "cam guide" sticky to help clear up the matter

 

LSA and ICL are two different specifications, but they are interrelated.

From the Comp Cams timing tutorial:
http://www.compcams.com/Technical/TimingTutorial/

The last thing we will discuss is the difference between intake centerline and lobe separation angle. These two terms are often confused. Even though they have very similar names, they are very different and control different events in the engine. Lobe separation angle is simply what it says. It is the number of degrees separating the peak lift point of the exhaust lobe and the peak point of the intake lobe. This is sometimes referred to as the "lobe center" of the cam, but we prefer to call it the lobe separation angle. This can only be changed when the cam is ground. It makes no difference how you degree the cam in the engine, the lobe separation angle is ground into the cam. The intake centerline, on the other hand, is the position of the centerline, or peak lift point, of the intake lobe in relation to top dead center of the piston. This can be changed by "degreeing" the cam into the engine. Figure 1 shows a normal 270 degree cam. It has a lobe separation of 110°. We show it installed in the engine 4° advanced, or at 106° intake centerline. The light grey curves show the same camshaft installed an additional four degrees advanced, or at 102 degrees intake centerline. You can see how much earlier overlap is taking place and how the intake valve is open a great deal before the piston starts down. This is usually considered as a way to increase bottom end power, but as you can see there is much of the charge pushed out the exhaust, making a less efficient engine. There is a recommended intake centerline installation point on each cam card, and it is important to install the cam at this point. As far as the mechanics of cam degreeing, Competition Cams has produced a simple, comprehensive video (part #190) that will take you step by step through the process.

Cam timing can be selected during the grinding process or altered after the fact at the cam or crank sprocket. Lobe separation angle cannot be changed once the cam is ground.

The cam card shown by the OP appears to be wrong. Installing a cam in the advanced or retarded position will alter the centerline of the intake lobe in relation to piston top dead center, thus subtracting (advancing) or adding (retard) to the intake center line specification of the intake lobe.