Split Lobe Separation Angles?

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roccodart440

roccodart440

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I came across a few cams the other day I've never seen. The LSA was split. As in LSA 108/116 and 108/120.

I've never seen this. Can anyone tell me what the effect this has? Or what the purpose of cutting a cam this way is?

This is one of the cams that caught my eye.
So for instance 254/[email protected], .587/.612, 108/120LSA?
 
Thanks. That helps. But why don't they just write the actual LSA?

So for example 108/120 = 114LSA

Why not just write 114LSA like you pretty much see everywhere?
 
roccodart440 said:
Thanks. That helps. But why don't they just write the actual LSA?

So for example 108/120 = 114LSA

Why not just write 114LSA like you pretty much see everywhere?
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Because you could have 110/118 or 112/116 and still have the same LSA.


That's why I cringe at how some guys select LSA. Or why. That's why I say set the events first and then the LSA will be close and you can manipulate things a bit to get what you want.


Intake valve closing is the big one for how many RPM you want to run per a given duration, and intake valve opening limits, or encourages reversion. It's all a balance.
 
Where are they getting 108/120 from vs. 114 is my question.

My cam doesn't list 2 LSA's. So that's what I'm trying to understand. Why are some illustrated like this and others are not?

Maybe I'm being thick headed in trying to understand this..
 
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Could they be listing the lobe center and the intake centerline?
 
The two numbers are where the intake and exhaust are at There max lift. Like said above, add the two centerline numbers, then divide by 2 to get the single listed/advertised number.
 
Here is another example. Yellow Rose, I included the valve events here just for you.

Smooth Idle (1200-5000 rpm range)

Intake Exhaust
Valve Lash .008 .012
Valve Lift . 440
Duration @ .050" 230
Lobe Center 102 / 118


Intake Opens 13BTDC
Intake Closes 37 ABDC
Exhaust Opens 45BBDC
Exhaust Closes 5 ATDC


It seems like they're using Lobe Centers, not LSA. IT also seems like this cam has advance cut into it.

On this cam for example.

The Exhaust lifter reaches the centerline of the exhaust lobe 118 crank degrees before TDC.
The Intake lifter reaches the centerline of the intake lobe 102 crank degrees after TDC.

Using Yellow Roses math, you can add them together to figure out that the distance from Exhaust centerline to Intake centerline is 220 crank degrees. The cam spins half the speed of the crank, 220 crank degrees is 110 cam degrees.

That makes the cam's LSA 110 cam degrees.
 
I'm pretty sure when cam mfr's advertise the ICL/LSA numbers, it's per their intended installation...

e.g., COMP cams likes to have (most of) their OTS cams to be installed at 106* ICL (because they grind them with 4* advance), but of course that is just what they say...the LSA of course, doesn't change as it's ground into the cam. So, regardless of whether you install it at 106* ICL per the provided instructions, straight up at 110* ICL, because you want to, or 102* ICL because you want to (and because maybe you want to boost your low/mid range a little, the LSA is still 110* in the case of most of COMPs legacy OTS grinds.

...or maybe I'm missing your point...?
 
roccodart440 said:
Here is another example. Yellow Rose, I included the valve events here just for you.

Smooth Idle (1200-5000 rpm range)

Intake Exhaust
Valve Lash .008 .012
Valve Lift . 440
Duration @ .050" 230
Lobe Center 102 / 118


Intake Opens 13BTDC
Intake Closes 37 ABDC
Exhaust Opens 45BBDC
Exhaust Closes 5 ATDC


It seems like they're using Lobe Centers, not LSA. IT also seems like this cam has advance cut into it.

On this cam for example.

The Exhaust lifter reaches the centerline of the exhaust lobe 118 crank degrees before TDC.
The Intake lifter reaches the centerline of the intake lobe 102 crank degrees after TDC.

Using Yellow Roses math, you can add them together to figure out that the distance from Exhaust centerline to Intake centerline is 220 crank degrees. The cam spins half the speed of the crank, 220 crank degrees is 110 cam degrees.

That makes the cam's LSA 110 cam degrees.
Click to expand...



Damn good math in this post. And it's correct. Now, for giggles, move either the intake or exhaust CL and see what it does. So start the intake sooner (wider LSA) or open the exhaust later (wider LSA) even though the duration stays the same.


You can play with that for a while and you can learn a lot. Every move changes the overlap triangle and that's what you want to watch when it comes to LSA, while considering low lift port flow characteristics.
 
yellow rose said:
Damn good math in this post. And it's correct. Now, for giggles, move either the intake or exhaust CL and see what it does. So start the intake sooner (wider LSA) or open the exhaust later (wider LSA) even though the duration stays the same.


You can play with that for a while and you can learn a lot. Every move changes the overlap triangle and that's what you want to watch when it comes to LSA, while considering low lift port flow characteristics.
Click to expand...

That will keep a person busy for a while, lol.

Thanks for the help here... While our camshaft selection may not always be in agreement you certainly are knowledgeable in that area, more so than I am. Can't dispute working through a reputable cam company and buying a custom grind is best. Bottom line is the world of camshafts is vast and there is more than one way to skin a cat. So long as the end user is happy with the build and it performs I'd say that is what matters.
 
roccodart440 said:
That will keep a person busy for a while, lol.

Thanks for the help here... While our camshaft selection may not always be in agreement you certainly are knowledgeable in that area, more so than I am. Can't dispute working through a reputable cam company and buying a custom grind is best. Bottom line is the world of camshafts is vast and there is more than one way to skin a cat. So long as the end user is happy with the build and it performs I'd say that is what matters.
Click to expand...


^^^^^^^^^^^^^^^^^^^^^^^This sums it up about as succinctly as one can.
 
I'm not a proponent of the "every engine needs a custom cam" idea myself but acknowledge that the best cam for any engine is one that is ground for it. I take the path of return on investment, i.e. value. If a shelf grind can deliver the performance needed and is less expensive it's more value to my customer. That being said there are times when something special will deliver something more, and in those instances I'll order custom. In terms of the theory being discussed when I order custom cams I tell the grinder where the ICL needs to be based on my own research. It's much more important to me than LSA for the reasons noted above. Just looking at LSA does not tell you where the most important event is (at least in most of my builds) - that being the intake closing event in relation to the piston's motion. The lobe centerlines are also more important with modern assymetrical lobe designs where the "centerline" is the center of max lift, not necessarily the physical center of the lobe.
 
moper said:
I'm not a proponent of the "every engine needs a custom cam" idea myself but acknowledge that the best cam for any engine is one that is ground for it. I take the path of return on investment, i.e. value. If a shelf grind can deliver the performance needed and is less expensive it's more value to my customer. That being said there are times when something special will deliver something more, and in those instances I'll order custom. In terms of the theory being discussed when I order custom cams I tell the grinder where the ICL needs to be based on my own research. It's much more important to me than LSA for the reasons noted above. Just looking at LSA does not tell you where the most important event is (at least in most of my builds) - that being the intake closing event in relation to the piston's motion. The lobe centerlines are also more important with modern assymetrical lobe designs where the "centerline" is the center of max lift, not necessarily the physical center of the lobe.
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I agree with all of this 1000000000% except (everyone knew there would be an except part right???) the cost issue. Unless you are pricing some unknown brand, most HFT and SFT cams are about $185.00 USFRN's. Give or take a couple of bucks. That's the same I pay for a custom Racer Brown, Cam Motion, Jones, Bullet etc.

Rollers are more, depending on core materiel, firing order etc, but retail for a custom roller is usually around $400.00 USFRN's. It goes up from there if you want a single swap firing or, or a 2 swap, different distributor gear material etc. it's the same for a custom grind.

So for me, the cost isn't even a factor. For some guys, who plan a day ahead, a 8-10 day lead time may kill them, but I plan ahead.
 
The issue with roller cam cost is really in the damned lifters
 
I rarely use rollers. I won't use a hydraulic roller without an arguement, but eventually the customer gets what they want.
That being said the money is better spent elsewhere if I don't need anything special to make the required power. It is a rare scenario that a shelf grind can't satisfy my power needs. But I know how to match components. It might be better for a novice to pick up a phone.
 
isn't there an issue with using hyd rollers without bushing the lifter bores?
 
roccodart440 said:
isn't there an issue with using hyd rollers without bushing the lifter bores?
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You can uncover the oil gallery. I think MRL has lifters that help with that.

If using a solid roller, you can either tube the passenger side gallery and block off the oil to tgphe drivers side at the number one main, or bush the lifter bores.
 
Full disclosure - I think I've actually built 3-4 hydraulic roller engines out of probably 60+ over the years. Solid rollers are preferred by me and I bush every block for them. But even those rare for my customer base. I've never seen, nor think I've ever heard about an issue with uncovering the tops of the lifter bores on a big block. I have heard about some smaller base circle cams leaking out the bottom - the roller supports on some lifters can uncover the oil passage - but that's why the deep bodied lifters exist. When it comes to hydraulic conversion rollers I have gone with Howards. At the time others' weren't available.
Small blocks cast and machined after the mid 70s, oiling problems are fairly common and I'm fairly sure Mike among others have lifters for that issue.
 
Here is the transcript with MRL



Jim,

No reason not to go with the Pro Plus, they have a bigger wheel and are more durable. You do not need to modify anything for a roller cam other than the mentioned dist gear, and you must run a cam button to control cam end play..

On Fri, Dec 9, 2016 at 8:49 AM, Farina, James <FarinaJ> wrote:

I need to order a set of lifters for my 440. I recently bought a custom comp cams roller cam. I have a few questions before I order

It looks as though the BBM Pro Sport and the BBM Pro Plus are my options. Is there any reason, other than cost to not choose the Pro Plus?

Last, other than changing the distributor gear, does anything else need to be modified to install this new cam? I.e. blocking oil passages, bushing lifter bores, etc?




Thanks,

Jim
--

Mike @ MRL Performance

989-845-1547


[email protected]


MRLPERFORMANCE.com
 
For hydraulic rollers, I agree. For a solid roller I will always bush the lifter bores.
 
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