Lobe Separation Angle (LSA)

[hoffman900]

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.

Highlights the important to check it at the valve. As you know, numbers at the camshaft are almost useless in those applications. Though measuring both, you can tell who designed for the application and who just copied and pasted from another application...

[ClassAct]

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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[ClassAct]

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.

^^^^^^^^^^^^^^^This too^^^^^^^^^^^^^^^^^^^^^^^^

And as I posted earlier, you get the guys who advocate for rolling a cam ahead 6 even 8 degrees to compensate for a bad combo or just the wrong cam for the application.

[CamKing]

And as I posted earlier, you get the guys who advocate for rolling a cam ahead 6 even 8 degrees to compensate for a bad combo or just the wrong cam for the application.

You need to clarify "rolling a cam ahead" to many, that means advancing the cam from a straight up location(ICL=LSA).
In that case, most cams need to be "advanced", because there are very few cases where the ICL and ECL need to be the same distance from TDC.
LSA is nothing but a number used to machine the cam.
Let's say I design a cam with a 102 ICL, and a 114 ECL. That just means that when we grind it, we grind the intake lobes 108 degrees from the exhaust lobes. That's why it's a 108 LSA.

[ClassAct]

And as I posted earlier, you get the guys who advocate for rolling a cam ahead 6 even 8 degrees to compensate for a bad combo or just the wrong cam for the application.

You need to clarify "rolling a cam ahead" to many, that means advancing the cam from a straight up location(ICL=LSA).
In that case, most cams need to be "advanced", because there are very few cases where the ICL and ECL need to be the same distance from TDC.
LSA is nothing but a number used to machine the cam.
Let's say I design a cam with a 102 ICL, and a 114 ECL. That just means that when we grind it, we grind the intake lobes 108 degrees from the exhaust lobes. That's why it's a 108 LSA.

I'm saying advancing the cam 6-8 degrees from the ICL called out on the cam card, if that makes sense. So, in your example above, ground on a 108 it would most likely install at 104. I've seen guys with the wrong cam and they would advance the cam from there. Maybe another 6 degrees, to 98. I forget what it was...a ford IIRC came in with the cam 8 degrees advanced and it was in at 96!!!!!!!!

Luckily, he had a mile of P/V on the intake or surely he would have smacked some valves that far ahead.

[CamKing]

I'm saying advancing the cam 6-8 degrees from the ICL called out on the cam card, if that makes sense. So, in your example above, ground on a 108 it would most likely install at 104. I've seen guys with the wrong cam and they would advance the cam from there. Maybe another 6 degrees, to 98. I forget what it was...a ford IIRC came in with the cam 8 degrees advanced and it was in at 96!!!!!!!!

Luckily, he had a mile of P/V on the intake or surely he would have smacked some valves that far ahead.

Yes, if you have to move it 6-8 degrees from where the cam company said to put it, either the cam is wrong, or you need a new cam company.
That being said, there's nothing wrong with a 98 ICL. We've had a bunch of limited class circle track engines, with restricted compression, and 390 carbs, where 98 ICL is optimum. A shorter duration cam on a later ICL would come off the corner just as hard, but not hold the power past peak, as long.

[Walter R. Malik]

I'm saying advancing the cam 6-8 degrees from the ICL called out on the cam card, if that makes sense. So, in your example above, ground on a 108 it would most likely install at 104. I've seen guys with the wrong cam and they would advance the cam from there. Maybe another 6 degrees, to 98. I forget what it was...a ford IIRC came in with the cam 8 degrees advanced and it was in at 96!!!!!!!!

That is simply not true, especially in turbocharged applications or any engine with a limited / restricted intake system and tuned exhaust system where the intake lobe is sometimes larger than the exhaust lobe ... advancing that correct camshaft also opens and closes the exhaust sooner, too.

OR, for a wide power curve when the exhaust is greatly restricted and the intake is not, is also a time when the valve timing is correct when the normal correct cam is advanced a bunch.

Different situations may call for some not so "normal" valve events.

[GARY C]

I'm saying advancing the cam 6-8 degrees from the ICL called out on the cam card, if that makes sense. So, in your example above, ground on a 108 it would most likely install at 104. I've seen guys with the wrong cam and they would advance the cam from there. Maybe another 6 degrees, to 98. I forget what it was...a ford IIRC came in with the cam 8 degrees advanced and it was in at 96!!!!!!!!

That is simply not true, especially in turbocharged applications or any engine with a limited / restricted intake system and tuned exhaust system where the intake lobe is sometimes larger than the exhaust lobe ... advancing that correct camshaft also opens and closes the exhaust sooner, too.

OR, for a wide power curve when the exhaust is greatly restricted and the intake is not, is also a time when the valve timing is correct when the normal correct cam is advanced a bunch.

Different situations may call for some not so "normal" valve events.

I think Class is saying the wrong cam for the application and the guy thinks advancing it will make it the correct cam and you are presenting a cam that with odd specs but is correct for the application, nitrous would be one of those applications where the cam may have excess exhaust lobe on a wider LSA and be more advanced then the LSA would suggest.

[digger]

Often if the engine likes the cam advanced it'll like the inlet advanced and exhaust retarded even more so, obviously depends on specifics.

I've seen engines like big cam advance and make more power everywhere, often where too much duration is used or on very low compression. When the cam is small I've seen the opposite

The LSA should not be refered to as how far apart the lobes are ground onto the stick because sometimes on sohc it's not the case

[GARY C]

Often if the engine likes the cam advanced it'll like the inlet advanced and exhaust retarded even more so obviously depends on specifics.

Yes in my limited experience with "nitrous cams" the early EVO hurt tq when the nitrous was off.

[Cris]

Dave:

I'm not sure you're original question every got answered. There is a simple formula to determine your lobe separation angle (LSA) from your intake centerline (ICL) and exhaust centerline (ECL). It is:

LSA = (ICL + ECL) / 2

It has nothing to do with lift points or anything else. It is simply a measurement at the peaks of the lobes. The ICL and ECL give you added information (in crank degrees) of where the peaks of the lobes reside relative to top dead center.

In your post you have a number of 180 which is odd?? For a cam with a 104 ICL and 104 ECL, the LSA is simply 104. A cam with a 100 ICL and 108 ECL would also have a LSA of 104

[DaveW]

Thanks for all the info, guys.

This question is related to another thread where I was asking about the reason for seeing a 2-point richer AFR between 4K and 5K, than the rest of the RPM range. I tried many different jets and emulsion tubes, with very little effect. Furthermore, my I/E lengths agree with Pipemax, so one of the only things left would be the cams. Someone mentioned that over-scavenging might be occurring at that point. So the only thing I can think of that might fix this would be to alter the cam timing. Again, the specs are Int dur (@ .050) = 266. Exh dur = 248. Lobe centers = 104. BTW, this is one of the more mild race cams for my car. BTW, since this is a road race application, I need a good power band from 4500 to 7500, but the car boggs down when I exit the slow corners (at 4000-4500). Admittedly a gearing change would be ideal, but that opens up a whole other can of worms.

[PRH]

I don’t agree that the intake c/l on the cam card is necessarily correct at all.

If it’s an off the shelf cam, the intake c/l is just where someone thought a good “overall” installed position would be....... which may not really be optimum for the particular engine the cam is going in.

From what I’ve seen through the years, the shelf cams usually have a certain amount of advance ground in....... and most shelf grinds from a particular company will have that same amount of advance.
Crane was usually 5*, UD was 6*, Comp, Lunati, Crower 4*.
The Lunati stuff that was done by Harold usually shows 6*.

Though I’ve gotten some shelf Comp bracket cams for Mopars that had 0.

I just put ‘em where I want......... sometimes it agrees with the card...... sometimes it doesn’t.

[GARY C]

Thanks for all the info, guys.

This question is related to another thread where I was asking about the reason for seeing a 2-point richer AFR between 4K and 5K, than the rest of the RPM range. I tried many different jets and emulsion tubes, with very little effect. Furthermore, my I/E lengths agree with Pipemax, so one of the only things left would be the cams. Someone mentioned that over-scavenging might be occurring at that point. So the only thing I can think of that might fix this would be to alter the cam timing. Again, the specs are Int dur (@ .050) = 266. Exh dur = 248. Lobe centers = 104. BTW, this is one of the more mild race cams for my car. BTW, since this is a road race application, I need a good power band from 4500 to 7500, but the car boggs down when I exit the slow corners (at 4000-4500). Admittedly a gearing change would be ideal, but that opens up a whole other can of worms.

I don't know what the combo is but 266 @ .050 seems big for a power band starting at 4500.

[DaveW]

Dave:

I'm not sure you're original question every got answered. There is a simple formula to determine your lobe separation angle (LSA) from your intake centerline (ICL) and exhaust centerline (ECL). It is:

LSA = (ICL + ECL) / 2

It has nothing to do with lift points or anything else. It is simply a measurement at the peaks of the lobes. The ICL and ECL give you added information (in crank degrees) of where the peaks of the lobes reside relative to top dead center.

In your post you have a number of 180 which is odd?? For a cam with a 104 ICL and 104 ECL, the LSA is simply 104. A cam with a 100 ICL and 108 ECL would also have a LSA of 104

Thanks Chris. Yes, I got it now. LCA is measured in crank degrees. LSA is measured in cam degrees. I was calculating LSA by subtracting the LCA (104) from BDC (180), then multiplying by 2 = 152 degrees.

Obviously, I have a way to go on engine tech, but I love it.