Lobe Separation Angle (LSA)

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DaveW
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Lobe Separation Angle (LSA)

Post by DaveW »

Why is the calculated value different than the actual measured value?

For example, my cams have intake and exhaust lobe centers of 104 degrees. So the calculated LSA is (104+104)/2 = 104. However the actual distance between the lobe centers is (180-104)*2 = 152 degrees.
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Re: Lobe Separation Angle (LSA)

Post by F-BIRD'88 »

You are confusing cam LSA the n crankshaft degrees (valve open close events) and cam lobe spread angle of the lobes on the cam in camshaft degrees.
Cam is 1/2 speed of crank rpm.
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Re: Lobe Separation Angle (LSA)

Post by F-BIRD'88 »

Also, further the math C/L of the lobes .050" event timing is not the same as the points of max lift of the cam lobes on a unsymmetrical cam lobe design.
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Re: Lobe Separation Angle (LSA)

Post by CamKing »

F-bird is correct
Intake and exhaust lobe centerlines(ICL & ECL) are the distance from the center of the lobe, to Overlap TDC, measured in Crank degrees
The LSA is the distance from the center of the exhaust lobe, to the center of the intake lobe, in camshaft degrees, with no relationship to the crank position.
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Re: Lobe Separation Angle (LSA)

Post by DaveW »

CamKing wrote: Sat Jun 29, 2019 4:45 pm F-bird is correct
Intake and exhaust lobe centerlines(ICL & ECL) are the distance from the center of the lobe, to Overlap TDC, measured in Crank degrees
The LSA is the distance from the center of the exhaust lobe, to the center of the intake lobe, in camshaft degrees, with no relationship to the crank position.
One spec is in crank degrees, the other is in cam degrees (apples and oranges). Got it, thanks.
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Re: Lobe Separation Angle (LSA)

Post by DaveW »

DaveW wrote: Sat Jun 29, 2019 4:55 pm
CamKing wrote: Sat Jun 29, 2019 4:45 pm F-bird is correct
Intake and exhaust lobe centerlines(ICL & ECL) are the distance from the center of the lobe, to Overlap TDC, measured in Crank degrees
The LSA is the distance from the center of the exhaust lobe, to the center of the intake lobe, in camshaft degrees, with no relationship to the crank position.
One spec is in crank degrees, the other is in cam degrees (apples and oranges). Got it, thanks.
One more thing, with regard to my cams, the LCA = LSA. I find that odd. Is that always the case, or only when ICL = ECL?
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Re: Lobe Separation Angle (LSA)

Post by CamKing »

DaveW wrote: Sat Jun 29, 2019 4:59 pm
DaveW wrote: Sat Jun 29, 2019 4:55 pm
CamKing wrote: Sat Jun 29, 2019 4:45 pm F-bird is correct
Intake and exhaust lobe centerlines(ICL & ECL) are the distance from the center of the lobe, to Overlap TDC, measured in Crank degrees
The LSA is the distance from the center of the exhaust lobe, to the center of the intake lobe, in camshaft degrees, with no relationship to the crank position.
One spec is in crank degrees, the other is in cam degrees (apples and oranges). Got it, thanks.
One more thing, with regard to my cams, the LCA = LSA. I find that odd. Is that always the case, or only when ICL = ECL?
When ICL and ECL are the same, LSA will be the same number. That's what some cam companies call "Straight Up" or "Zero Advance"
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Re: Lobe Separation Angle (LSA)

Post by DaveW »

CamKing wrote: Sat Jun 29, 2019 5:04 pm
DaveW wrote: Sat Jun 29, 2019 4:59 pm
DaveW wrote: Sat Jun 29, 2019 4:55 pm

One spec is in crank degrees, the other is in cam degrees (apples and oranges). Got it, thanks.
One more thing, with regard to my cams, the LCA = LSA. I find that odd. Is that always the case, or only when ICL = ECL?
When ICL and ECL are the same, LSA will be the same number. That's what some cam companies call "Straight Up" or "Zero Advance"
Thanks Mike. I'm obviously a bit of a newbie on this.

But while I'm at it . . . is there any formula or rule of thumb regarding the effects of altering the cam timing? I understand that advancing the cam timing will shift the power band downward, and retarding will shift it higher. My question is, by how much, in terms of RPM shift vs. degrees of cam advance/retard from manufacturer's spec?
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Re: Lobe Separation Angle (LSA)

Post by CamKing »

DaveW wrote: Sat Jun 29, 2019 6:23 pm My question is, by how much, in terms of RPM shift vs. degrees of cam advance/retard from manufacturer's spec?
Sorry, but there's too many variable to predict how a certain cam, is going to react to a cam timing change, in a certain engine.
Cam size, Engine size, port size, compression, and how close the cam was to correct, before the move, all play a role, in how a cam timing move, will effect an engine.
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Re: Lobe Separation Angle (LSA)

Post by ClassAct »

DaveW wrote: Sat Jun 29, 2019 6:23 pm
CamKing wrote: Sat Jun 29, 2019 5:04 pm
DaveW wrote: Sat Jun 29, 2019 4:59 pm

One more thing, with regard to my cams, the LCA = LSA. I find that odd. Is that always the case, or only when ICL = ECL?
When ICL and ECL are the same, LSA will be the same number. That's what some cam companies call "Straight Up" or "Zero Advance"
Thanks Mike. I'm obviously a bit of a newbie on this.

But while I'm at it . . . is there any formula or rule of thumb regarding the effects of altering the cam timing? I understand that advancing the cam timing will shift the power band downward, and retarding will shift it higher. My question is, by how much, in terms of RPM shift vs. degrees of cam advance/retard from manufacturer's spec?


I have a "general" rule of thumb that I've used over the years (I'd love to hear what others think) and that is, if I have to move the ICL more than 2 degrees one way or the other from what the cam grinder said it shoud be installed, I think that cam I wrong.

I say that, because back when I was in HS, all the heroes wanted to run super big cams, bottom of the right hand page stuff and then had stock converters, no gear and crap like that. Then they would install the cam 4-6 degrees ahead of what was called for.

And they were still pigs. I made money off those guys. It always seemed to me if you and to move the ICL that far, all the timing events were incorrect, and you are just applying a band aid where an amputation is required.
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Re: Lobe Separation Angle (LSA)

Post by Newold1 »

A very simplified way to look at and consider the LSA of a camshaft is simply the distance measured in degrees between the centerline of the camshaft intake lobe and the exhaust lobe. Taking a fixed cam with a certain LSA and advancing or retarding the camshaft installed location does not make more power. It simply just moves the engines power band up or down at that rpm point. This is why just duration and lift numbers along with LSA is not the be all tell all things to consider. It's the timing of the opening and closing points for the valves that optimize for that engine combination and create the most power. This is why camshaft experts like Mike make a successful business producing camshafts for their customers because they apply a multitude of factors in the design of the camshaft and how it will be used.
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Re: Lobe Separation Angle (LSA)

Post by AA Performance »

Newold1 wrote: Sat Jun 29, 2019 10:28 pm A very simplified way to look at and consider the LSA of a camshaft is simply the distance measured in degrees between the centerline of the camshaft intake lobe and the exhaust lobe. Taking a fixed cam with a certain LSA and advancing or retarding the camshaft installed location does not make more power. It simply just moves the engines power band up or down at that rpm point. This is why just duration and lift numbers along with LSA is not the be all tell all things to consider. It's the timing of the opening and closing points for the valves that optimize for that engine combination and create the most power. This is why camshaft experts like Mike make a successful business producing camshafts for their customers because they apply a multitude of factors in the design of the camshaft and how it will be used.
[/quote
Are you saying that if 2 cams have the same duration, and L/S , the opening and closing events can be different? Wouldn't that change the L/S angle, assuming its a symmetrical design?
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Re: Lobe Separation Angle (LSA)

Post by Newold1 »

Of course LSA's will change with changes in durations but what I was trying to get across in my simplified comment was that lots of performance enthusiasts get hung up on talking just duration, max lift and LSA and then throw in a little talk about advancing or retarding the cam. Durations and LSA's can be the same on two different camshafts but depending on where the IVO, IVC and EVO and EVC are located the performance of those two camshafts can have a major affect on the ultimate power the engine develops based on rpm ranges desired. Their is so much more to camshaft engineering than most users ever study and learn and the missed potential they leave on the "bench" is unfortunate.
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Re: Lobe Separation Angle (LSA)

Post by PRH »

My experience has been that advancing or retarding a cam will often not result in the operating range shift most people associate with moving the cam.

Often times the motor just makes more/less power everywhere when the cam is moved.

For example, perhaps retarding a cam a couple degrees on a particular combo may theoretically make more power at the upper most rpms........ but if that’s at an rpm the motor will never reach(and is a point never seen during testing), then the effective result is just a net loss........ at all points within the observed powerband.

I’ve seen that play out a few times.
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Re: Lobe Separation Angle (LSA)

Post by Walter R. Malik »

DaveW wrote: Sat Jun 29, 2019 4:23 pm Why is the calculated value different than the actual measured value?

For example, my cams have intake and exhaust lobe centers of 104 degrees. So the calculated LSA is (104+104)/2 = 104. However the actual distance between the lobe centers is (180-104)*2 = 152 degrees.
Where did that 180 come from? Crankshaft degrees and camshaft degrees read differently.
Lobe separation is not the same thing as installed intake lobe center and are often confused with one another.

OHC engines with non linear valve angles and direct acting rocker arms are all over the place at the camshaft; especially slider rockers.
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