Lets talk CAM LSA - Vintage Mustang Forums
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post #1 of 17 (permalink) Old 07-02-2019, 01:27 PM Thread Starter
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Lets talk CAM LSA

Just want to see if I'm correct in my understanding of CAM LSA

A "typical" street car CAM SLA is between 110-112?

The lower the LSA - the less amount of time the valves open/close but increases the frequency? A larger lift is desirable here to maximize flow but you need to be concerned about piston to valve clearance right?

Larger LSA indicates the longer the valves stay open effectively increasing the flow (due to length open) with smaller valve lift?

LSA in this range looses low end torque as opposed to something in the 108-110 range?

Am I in the ballpark here?

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post #2 of 17 (permalink) Old 07-02-2019, 03:18 PM
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A narrow LSA of 106-108 has a lot of valve overlap, poor idle, and generally narrower power band in the upper rpms.

A wide LSA of 110-112 has less overlap, smoother idle, wide power band and generally better on the street.
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post #3 of 17 (permalink) Old 07-02-2019, 05:55 PM
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Well, this thread will likely get interesting. LSA is a number that was created as a generalization of how a cam may act. Two cams can have the same advertised LSA and act very differently. You'll learn and understand more about how a particular camshaft will behave if you take the time to understand how the valve events affect the engine. That's where LSA derived from, and those are the numbers that matter.


But as a general rule, narrow LSA will make the engine peak and fall off faster, but possibly make more power at a given RPM. Wider LSA is better for power adders and gives a broader power range. Again, these are just generalization. My cam had a advertised LSA of 106 and we sprayed the crap out of it. It's a bad practice to pick a cam based on LSA.

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post #4 of 17 (permalink) Old 07-02-2019, 06:59 PM
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Quote:
Originally Posted by MrFlash View Post
A narrow LSA of 106-108 has a lot of valve overlap, poor idle, and generally narrower power band in the upper rpms.

A wide LSA of 110-112 has less overlap, smoother idle, wide power band and generally better on the street.
I believe your backwards on that, for example
B303 has LSA of 112 480/480 lift lots of over lap ,lumpy idle ect

E303 has LSA of 110 498/498 lift not as much over lap ,smoother idle more computer friendly ect

This thread




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post #5 of 17 (permalink) Old 07-02-2019, 07:15 PM
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The LSA number by itself is not telling you all you need to know.
Duration at .050 plus LSA tells you overlap.
As said earlier, more overlap equals rougher idle and poor low end.
Street cams are always a compromise. You have to compromise high end power for low rpm drivability.
For the letter cam example above, the E303 has less duration than the B303. So the less duration with a narrower LSA still may have less overlap.
Try this for interesting reading
https://www.hotrodders.com/forum/any...ds-459809.html
https://www.chevelles.com/forums/13-...placement.html
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post #6 of 17 (permalink) Old 07-02-2019, 07:29 PM
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All good info above. Here is a little easy reading which confirms the above.

https://www.onallcylinders.com/2012/...et-cam-part-1/

https://www.enginebuildermag.com/201...g-performance/

...Marco

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post #7 of 17 (permalink) Old 07-02-2019, 07:47 PM
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Quote:
Originally Posted by John_in_SC View Post

The lower the LSA - the less amount of time the valves open/close but increases the frequency?

[snip]

Larger LSA indicates the longer the valves stay open effectively increasing the flow (due to length open) with smaller valve lift?
The three primary stats on a CAM are, lift, duration and LSA. There are more factors but those are the traditional three.

The characteristics you are describing above with length of time the valves open/close is governed by the "duration" on the camshaft, not LSA.

LSA = Lobe Separation Angle and when combined with duration will impact the amount of overlap between the intake and exhaust valves.

Here is a pic illustrating the difference in LSA of 102* vs 116*. See how the dotted line lobes are closer to each other and would have slightly more overlap?



Taken from this much more lengthy article on the subject of LSA which I didn't bother reading but wanted to use the illustration from. https://www.cartechbooks.com/techtips/camshafts1/
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post #8 of 17 (permalink) Old 07-02-2019, 08:58 PM Thread Starter
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Quote:
Originally Posted by sportsroof69 View Post
Well, this thread will likely get interesting......
I seem to have a developed a habit of doing that as of late.....

Trying to better understand LSA/Duration/Lift and CAM selection. I have developed a thirst for knowledge in this area. I keep reading and reading.

One of things on the table for me lately is a CAM/lifter combo. Streetability is a factor (want to be able to drive it to drop the kids off at school) but also looking for that aggressive street CAM.

My intake (performer RPM) and cylinder heads seem to be rated at 1800-6500 RPM and i'd like to pull hard through/past 6K. Willing to give up low end for mid-high pull. Edel 7122 seems to be the "off the shelf" match for the rest of my setup but the Comp 274H has caught my eye. My current CAM def pulls hard but is rated through 5800.

Calls to EDEL and COMP have both lead to these two options but I like to trust but verify.

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post #9 of 17 (permalink) Old 07-02-2019, 09:07 PM Thread Starter
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I should add one other thing. After the tuning I've just done on the CARB (quite a bit) - I'm going to back to dyno to get some RWHP numbers. If I'm over 300 I'm content where I am and will look at other things. Last DYNO (pre tune) had me at 284HP/301 torque - which is alot of fun, but I want more.

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post #10 of 17 (permalink) Old 07-02-2019, 09:24 PM
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This is a bit off topic but it does involve LSA and it involves a Chevy...my 2013 corvette 427 convertible (LS7)...

I looked up the cam specs of the LS7 a while back and was surprised to see that the LSA is 121 degrees...yikes, and it is a short duration high lift roller cam (210 to 220 duration and nearly .600 lift). It peaks horsepower at about 6300 rpm and will idle smooth all the way down to stall...thankfully because when i'm in traffic, I can just put it into 1st or 2nd and take my foot off the gas and just creep along smoothly. Otherwise, a lopey cam would be a nightmare in traffic.

Anyhow, one might look at the specs for a cam like this and not think it can be part of a high horsepower 7000 rpm engine, but it is because the cam only plays part of the role in the overall performance of an engine. Heads, intake, exhaust etc complete the package.

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post #11 of 17 (permalink) Old 07-02-2019, 09:51 PM
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When selecting a camshaft the first thing I consider is how much do I want to spend on valve springs.

Most fully assembled aftermarket heads include valve springs that can handle up to .550 lift.
So I will choose a camshaft with around .510 lift with stock 1.6 ratio rocker arms.
That way if I choose to switch to 1.7 rockers I’ll still be under.550 lift.

I also prefer camshafts with more lift and duration on the exhaust side.

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post #12 of 17 (permalink) Old 07-02-2019, 10:07 PM Thread Starter
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Quote:
Originally Posted by MrFlash View Post
Most fully assembled aftermarket heads include valve springs that can handle up to .550 lift.

Thats right where I am on my Performer RPM heads.

BTW - like your avatar. I happen to be Signal myself.

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post #13 of 17 (permalink) Old 07-02-2019, 10:30 PM
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Quote:
Originally Posted by Chad-1stGen View Post
The three primary stats on a CAM are, lift, duration and LSA. There are more factors but those are the traditional three.

The characteristics you are describing above with length of time the valves open/close is governed by the "duration" on the camshaft, not LSA.

LSA = Lobe Separation Angle and when combined with duration will impact the amount of overlap between the intake and exhaust valves.

Here is a pic illustrating the difference in LSA of 102* vs 116*. See how the dotted line lobes are closer to each other and would have slightly more overlap?



Taken from this much more lengthy article on the subject of LSA which I didn't bother reading but wanted to use the illustration from. https://www.cartechbooks.com/techtips/camshafts1/
LSA is far from a primary stat. The only reason cam manufacturers even publish this number is for the general enthusiast that doesn’t understand timing events. If you talk to a custom cam builder, they won’t even discuss LSA with you.
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post #14 of 17 (permalink) Old 07-02-2019, 10:33 PM
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Quote:
Originally Posted by blkfrd View Post
This is a bit off topic but it does involve LSA and it involves a Chevy...my 2013 corvette 427 convertible (LS7)...

I looked up the cam specs of the LS7 a while back and was surprised to see that the LSA is 121 degrees...yikes, and it is a short duration high lift roller cam (210 to 220 duration and nearly .600 lift). It peaks horsepower at about 6300 rpm and will idle smooth all the way down to stall...thankfully because when i'm in traffic, I can just put it into 1st or 2nd and take my foot off the gas and just creep along smoothly. Otherwise, a lopey cam would be a nightmare in traffic.

Anyhow, one might look at the specs for a cam like this and not think it can be part of a high horsepower 7000 rpm engine, but it is because the cam only plays part of the role in the overall performance of an engine. Heads, intake, exhaust etc complete the package.
Actually, it’s because there is more to the story than LSA. LSA is a made up number. Timing events are crucial.
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post #15 of 17 (permalink) Old 07-03-2019, 12:04 AM
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Swiped from the Lunati website: https://www.lunatipower.com/cam-spec-terms


DURATION

Duration is the angle in crankshaft degrees that the valve stays off its seat during the lifting cycle of the cam lobe.

How is it measured?
Advertised duration is the angle in crankshaft degrees that the cam follower is lifted more than a predetermined amount (the SAE standard is 0.006") off of its seat. Duration @.050" is a measurement of the movement the cam follower, in crankshaft degrees, from the point where it’s first lifted .050" off the base circle on the opening ramp side of the camshaft lobe, to the point where it ends up being .050" from the base circle on the closing ramp side of the camshaft lobe. This is the industry standard, and is a good value to use to compare cams from different manufacturers. Both are usually measured with a dial indicator and a degree wheel. What does it do?

What does it do?
Increasing duration keeps the valve open longer, and can increase high-rpm power. Doing so increases the RPM range that the engine produces power. Increasing duration without a change in lobe separation angle will result in increased valve overlap.

LOBE SEPARATION

Lobe separation is the angle in camshaft degrees between the maximum lift points of the intake and exhaust valves. It is the result of the placement of the intake and exhaust lobes on the camshaft.

How is it measured?
Cam Lobe Separation Lobe separation can be measured using a dial indicator and a degree wheel, but is usually calculated by dividing the sum of the intake centerline and the exhaust centerline by two.

What does it do?
Lobe separation affects valve overlap, which affects the nature of the power curve, idle quality, idle vacuum, etc.

OVERLAP

Overlap is the angle in crankshaft degrees that both the intake and exhaust valves are open. This occurs at the end of the exhaust stroke and the beginning of the intake stroke. Increasing lift duration and/or decreasing lobe separation increases overlap.

How is it measured?
Overlap can be calculated by adding the exhaust closing and the intake opening points. For example, a cam with an exhaust closing at 4 degrees ATDC and an intake opening of 8 degrees BTDC has 12 degrees of overlap. But keep in mind that since these timing figures are at 0.050" of valve lift, this therefore is overlap at 0.050". A better way to think about overlap is the area that both lift curves overlap, rather than just the crankshaft angle that both valves are open. Therefore, one can see that decreasing the lobe separation only a few degrees can have a huge effect on overlap area.

What does it do?
At high engine speeds, overlap allows the rush of exhaust gasses out the exhaust valve to help pull the fresh air/fuel mixture into the cylinder through the intake valve. Increased engine speed enhances the effect. Increasing overlap increases top-end power and reduces low-speed power and idle quality.

CENTERLINES

The intake centerline is the point of highest lift on the intake lobe. It is expressed in crankshaft degrees after top dead center (ATDC). Likewise the exhaust centerline is the point of highest lift on the exhaust lobe. It is expressed in crankshaft degrees before top dead center (BTDC). The cam centerline is the point halfway between the intake and exhaust centerlines.

ADVANCE/RETARD

Cam Advance and Retard Advancing or retarding the camshaft moves the engine’s torque band around the RPM scale by moving the valve events further ahead or behind the movement of the piston. Typically, a racer will experiment with advancing or retarding a cam from "straight up" and see what works best for their application. Lunati camshafts are ground to provide maximum performance and are designed to be installed to the specifications listed on the cam card.

How is it measured?
A cam with a 107 degrees intake lobe centerline will actually be centered at 103 degrees ATDC when installed 4 degrees advanced.

What does it do?
Advance improves low-end power and response. For a general summary of the affects of camshaft timing, refer to the following tables:

Advance
• Begins intake event sooner
• Opens intake valve sooner
• Builds more low-end torque
• Decreases piston-to-intake-valve clearance
• Increases piston-to-exhaust-valve clearance

Retard
• Delays intake event
• Opens intake valve later
• Builds more high-end power
• Increases piston-to-intake-valve clearance
• Decreases piston-to-exhaust-valve clearance

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