Excuse my ignorance but I come from the SBC world and the LS world is new to me. I do understand what lobe separation and lobe centerline is, but I see 112 +2 or 114 + 4 all the time regarding cam specs and don't know exactly what you mean.

I'm guessing 112 + 2 means 112 lobe separation but installed at 110 (advanced 2 degrees) but I am not 100% sure this is what it means.

Could anyone shed light on this for me please ?

 

You are close. It means the advance is ground into the cam. So for example, 112+2, the intake is ground on a 110 centerline and the exhaust is ground on a 114 centerline. You would install the cam straight up.

 

Not sure I understand, what is the lobe separation on the example you're giving ? Separation is diffrent than centerline and not sure which is which in that kind of definition

 

The example that you're using has no bearing on ls, sbc, gm, ford, mopar, or a Murray lawn mower. So don't look at it as "ls". Lobe separation angle (LSA, the "112") is the angle between the intake lobe and the exhaust lobe. It's designed into the cam when it's ground, and can't be changed without regrinding the cam. Place the cam at eye level in front of you, pointing straight forward. Look at the intake and exhaust lobe tip for the first set. Envision an imaginary line running down from each lobe tip to the very center of the cam. That V that those two lines form is your LSA, and in the example you're using, that V forms a 112* angle, when laid over sideways.

lobe CENTERLINE angle (LCA) is the suggested installation point of the lobe (whether it be intake or exhaust, but normally the numbers given are for the intake lobe). It's the relationship between piston position, and the peak valve lift of that lobe (be it intake or exhaust being referred to)

so, in your example, it means that if you (as stated by Darth) install said cam "straight up" (dot to dot on a factory timing set), your intake valve will be at peak valve lift at 110* after the piston has past top dead center. The "+2" in your example means that the designer/grinder ground the cam with 2* of advance, so the example cam will (theoretically) wind up at the position of 110* ATDC when installed dot to dot (straight up). Some things to consider.........NEVER just slap a cam in dot to dot without checking it with a degree wheel. Doing so has burned tens of thousands of people through the decades. Plus, doing so just promotes shoddy workmanship. Bad habits. So always check the cam. And, you can decide to install the cam at any centerline you want. 110* isn't carved in stone (like the 112* is). This is where tuning the combination comes into play. Anyhow, that's the gist of it. Make a little more sense to you now?

 

I'm far from being an expert here but I like this graph to illustrate LSA.

The numbers on this don't match any you quoted but the concept is valid. A cam can be installed at different timing points, generally with an adjustable timing set. The ICL is usually used as a reference. If the cam is a 113 LSA for example it can be installed with the intake centerline at 111 degrees which would be +2 or advanced 2 degrees. Keep in mind when you do this the exhaust is also moving. In my example the ecl would be at 115.

My understanding, hopefully correct, is that when the advance is "ground in" all they are doing is changing the relationship between the cam lobes and the dowel pin for the cam gear. That way when you align the dots the advancing is done without using a degree wheel and adjustable timing set.

 

guys, I know what lobe separation and lobe centerline is, it's just the 112 +2 or 114 +4 jargon that I don,t understand.

in my world, a cam that has 110 separation and is installed at 108 intake centerline is 2 degrees advanced. I can install it wherever i want, and I do understand that separation is built into the cam, and sometimes the dot to dot has it installed at 2 advanced already and I can change that by degreeing it. Can someone define let's say what 112 +2 means ?

 

I thought I just did that.

 

I sort of thought I did too. And so did Darth. 112 means that the cam is ground on a 112* LSA. +2 means that the grinder is suggesting it be installed at 110* atdc for all the opening/closing points to correctly match what is stated on the cam card. He/she/it designed the cam with 2* advance built in. I think it's the + that's confusing you because 112+2=114. So look at it as 112-2=110 if that helps. Many cam designers/grinders build a little advance into the cam. Some do it to account for timing chain stretch over time.........some do it to bandaid the fact that too many people over-cam an engine. Stare straight at a degree wheel. See the 112* mark? By advancing the cam, you're opening the valve a little earlier. 2* in this case. So, on your degree wheel, move BACKWARDS 2* from the 112 mark and you have..........110. Tada! 2 degrees earlier than 112. Does that help?

 

112+2 means the advance is ground into the cam

 

Ok now i get it. 112 + 2 means that the separation is 112 and aligning it dot to dot should (I say should, but I know it has to be checked with a degree wheel) have the intake centerline at 110 degrees. Ok. Do I understand it correctly ? Maybe I'm a bit slow, sorry guys...

 

yup, you graduated!

 

Based on what I've read, the advance is ground in the cam to create better off idle characteristics and better low end torque.

 

You answered yourself.

 

It is sort of a natural outcome to the way cams are speced. Think of a single pattern cam with no advance. Your intake and exhaust lobe are the same size and in the same location. So a 224/224-112 will close intake and open exhaust at 44 degrees. Intake will open and exhaust will close at zero. But that is not normal. usually, exhaust will open 6-12 degrees earlier than intake closes. 52 vs 44 for this example. So even if it's a single pattern 224/224, that will automatically make the cam 224/224-116+4. But then you also typically see exhaust duration larger than intake. So make the exhaust 232, and your exhaust centerline drops back to 116, so now the spec is 224/232-114+2.

Pretty much as long as the intake valve closes at a lower number than the exhaust valve open, the Intake centerline will calculate as if advanced.

It is a generality, but it is rare that it does not hold true.

 

I just realized what your avatar is.. Nice.

 

Lol thanks. My wife is a good sport.