I feel like I knew how to do this at one point and now I can't figure it out again...

I've got a cam with a 110 Lobe Separation Angle (LSA), it has 4 degrees of advance ground in for a 106 LCA -calculating the intake and exhaust lobe centerlines should be @#%$@#% easy with this information but I'm getting tripped up.


In my mind I can see the 110 degrees separating the two lobes -if I try to do this with a cam ground straight up, I'd think that I just start at straight-up 180 degrees and subtract half of the LSA from 180 and that should give me the intake center line and add half the LSA to straight up 180 and that should give me the exhaust centerline (then I just move both lobes 4 degrees forward, but those numbers make no sense.)

Half of 110 =55; 180-55 = 125; 180+55= 235 ---Those numbers are non-sensical for lobe centerlines. I thought maybe straight up is 90 so I add 55 to 90 and get 145 -also nonsensical for a lobe centerline #...


What the @#%^@#$ am I doing wrong?? This was stupid easy at one point... The more I learn, the dumerer I get...


Adam

 

I thought it was as simple as ICL = LSA - advance. So in your case the ICL should be 106. The exhaust would be 114.

 

you know i just read an article on this let me find it.....

https://www.cartechbooks.com/techtips/camshafts1

 

You're of course correct; what makes no sense is why the ICL and ECL are numbered the way that they are.


The LSA makes complete sense- literally the number of crank degrees that separate the two lobes- best naming and numbering system EVER.


So let's use an example of a 110 LSA cam with zero advance/retard ground in installed straight up:
The Lobe Separation Angle would be 110: there are 110 crank degrees separating the peaks of both lobes- makes perfect sense.

In this case the Intake Centerline is called "110 degrees" and so is the Exhaust center line??!?? What the heck is that 110 degrees supposed to represent??!? 110 degrees in relation to what? -If the distance between the two lobes is 110 crank degrees and the cam is installed "straight up" and ground "Straight up" then the intake centerline's position is actually 55 crank degrees before TDC and the exhaust centerline is 55 degrees AFTER TDC. Why aren't these positions called "-50 degrees" or "+50 degrees"??


I think what's driving me bonkers (today) is this diagram:




If the distance between the intake lobe's peak/centerline and the exhaust lobe's peak/centerline is 110 degrees TOTAL, then the distance between TDC and one of the lobe's intake centerlines can NOT be 110 degrees. -If each one is 110 degrees, then the total/LSA 220 degrees. Why doesn't addition work with cams?!?
What kind of engineering world exists where 110+110=110?!?


Adam

 

Here's a better diagram of the same thing from DesktopDyno 2003.

I like it better in that it shows crank degrees across the top the entire time:



This is a "110 LSA" cam installed straight up; the intake centerline is "110" and the exhaust center line is "110".

I thought the intake/exhaust centerlines were a numerical description of their positions, in which case "250 degrees" (360 -110)would be a better description for the exhaust centerline (or at least "-110 degrees") and "470 degrees" (360 -110)would be a better description for the intake centerline's position (or at least +110 degrees). -That's ASSUMING that the lobe centerline is a number that's supposed to represent it's POSITION relative to crank rotation / TDC.

-Also if the exhaust lobe center is hit 110 degrees before TDC and the intake lobe center is hit 110 degrees AFTER TDC, then they're 220 degrees apart from each other, which is what I THOUGHT an LSA's value was supposed to represent. Why isn't the LSA 220 then?


-Even the diagram above shows the distance between the two lobe centerlines going from about 250 degrees to 470 degrees (470-250=220). Why the @#% isn't the LSA "220"?

Something in this numbering system is wack!

Adam

 

OHHH it's because LSA is measured in CAMSHAFT angles and ECA and ICA are measured in crankshaft angles...

So the LSA really IS 220 crank degrees, it's just measured in cam degrees??.. I think...

Who the @#%# decided that you should measure the POSITION of a camshaft's lobes in crank angles but the distance between them in cam angles?!? -I hope they're long dead...

That's like unconstitutionally cruel and unusual punishment to someone who's newish to this hobby.
I might not be smart, but I sure as hell know that 110+110 does NOT equal 110... (Except when measuring cams, then 110+110=110 !@#%!@!@!!!)

Adam

 

Of course. Why would anyone use the measurement base when they can use 2 to make it 4 times as complex.https://m.harborfreight.com/1-in-tra...tor-63521.html. https://m.harborfreight.com/multipos...ment-5645.html. https://www.google.com/search?ie=UTF...ZGRMPFHL5RrcM:

 

Find your centerline. Then check calculations for accuracy.

 

Look at th graph you provided here on the bottom. With TDC =0 you got -110 out to the left for exhaust centerline and 110 degrees to the right for intake center line. If you have ever degreed a camshaft you would understand better. The wheel goes only 360 degrees. 0 and 360 is TDC. When you read valve events they are writing in relation to degrees before TDC, after TDC and also BDC.

 

You have cam degrees and crank degrees. Have to use both cuz the 2 have to interface with each other. But neither LCA needs to be 110 degrees from tdc.

 

Jesus Christ.... talk about making the easiest thing in the world difficult and confusing.

If the LSA is 110 and the Intake CL is advanced 4* (106) then the Exhaust CL is 114.

Because the 2 lobes are physically on the same stick and at fixed points, in relation to one another, when you advance one CL you retard the other CL the same amount.

Will

 

I believe you are advancing or retarding both the same amount with offset keyway.

 

I get what everyone on here is saying. The LSA is fixed and when you rotate the cam both lobes move together. I think everyone here has the context, so it makes sense, but stop and think for a second with new eyes like you've never seen these specs before and it's rather bonkers.

The Exhaust Centerline (ECA) and the Intake Center Line (ICA) are measured in CRANK degrees and is a numeric value that's supposed to indicate their distance from TDC. (Negative numbers for one and positive for the other would've been less confusing to show whether they're before or after TDC rather than a number that just represents DISTANCE from TDC without timing -but that's a minor compliant.)

-You then move on to the next cam spec, Lobe Separation Angle, which is supposed to be a measure of the distance between the two lobe centers, and all of a sudden you just switch from Crank Degrees to Cam Degrees. Just keep it all in the same units; don't randomly pick and choose which specs are in crank degrees and which are in cam degrees! It's made way more confusing because the LSA really is the # of degrees between the ECA value and the ICA value (in crank degrees) -add the two together and you get the LSA (in crank degrees) -keeping it all under one reference (crank degrees) helps you to visualize the distance between the two and their relation to the crank. It's particularly strange with a 110 LSA installed straight up as you get an ICA = 110, ECA= 110; then add ICA+ECA to get your LSA and it's 220 degrees (but you have to divide by 2 just for LSA to convert back into cam degrees and now 110+110=110).



Keeping all the cam specs in either cam degrees OR crank degrees was a no-brainer. -I understand someone would look at a cam with an LSA of "220" crank degrees and say "that's not a 110 degree angle!" but that bolsters MY point as that would be obvious and less confusing than mixing and matching cam spec #'s between cam degrees and crank degrees.

I fully admit its a bit less confusing when you're not dealing with a 110 LSA cam installed straight up, but this makes Imperial measurements of volume look smart and simple...


Adam