High duration/low lift VS Low duration/high lift
11-02-2010, 08:02 PM
#21
It's a cam spec that is the result of the VEs, not the other way around. It doesn't say anything by itself, especially without knowing ICL. Overlap area is the important number, which is dictated by duration, lobe intensity (lift), and LSA. The actual centerlines and lobe asymmetry move the overlap event. All of this is relative to the engine combination, otherwise we're just babbling about theory.
11-02-2010, 08:29 PM
#22
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ok.. centerlines are important. with a given centerline you calculate LSA. LSA is the common reference. Thus the reason it is used. whether an ICL is 106 or 110, the LSA is still important. saying that by itself it doesn't say anything is retarded.. if you have a given LSA with an unkown centerline it will still help determine the behavior of the cam. If i tell you that the LSA on a given cam is 112, that still gives a direct reference to the centerline of the two lobes whether their points on the cam are known or not. I'm not trying to say that LSA is the only thing you need to look at, but it's a pretty big one. Overlap is very important as well. It's can be calculated using the LSA... when that overlap occurs can be determined after knowing the ICL. LSA is directly related to a camshafts performance. There is no arguing that.
11-03-2010, 02:21 AM
#23
Staging Lane
Wicked94Z is saying two things, and he's right.
1. That this thread should have been posted somewhere else.
2. There are only vague trends that follow each spec, and ignoring the complete package will only get you the best results with dumb luck.
1. That this thread should have been posted somewhere else.
2. There are only vague trends that follow each spec, and ignoring the complete package will only get you the best results with dumb luck.
11-03-2010, 11:20 AM
#24
whether the thread belongs here or not is irrelevant. OP has a question and we are trying to answer it. Also, ignoring the whole package won't give you optimum results. But, if you don't know anything about the specifics, (OP) then you can't exactly use them for reference. which is why everyone looks at LSA instead of ICL and all of the other variables. If everyone were a top engine builder, I'm sure they would use those specs, but since most people don't even know what ICL is, they use what they know (which is what the cam manufacturers let them know lol)
11-05-2010, 03:03 AM
#25
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Guys, especially wicked, this is in the AET section for a reason. This is about theory, what might be the advantages of one combo of specs vs another different one. Lets keep it that way.
11-11-2010, 03:08 AM
#27
It's a cam spec that is the result of the VEs, not the other way around. It doesn't say anything by itself, especially without knowing ICL. Overlap area is the important number, which is dictated by duration, lobe intensity (lift), and LSA. The actual centerlines and lobe asymmetry move the overlap event. All of this is relative to the engine combination, otherwise we're just babbling about theory.
so ur saying that lsa is just a number, had by other numbers(ve's). like u said, doesnt mean you cant USE that number.
stop and think, EVERY number that has to do with a cam shaft or motor in general is a number derived from another set of numbers.
for example.
lift is total lobe height minus base circle.
cubic inches, bore and stroke
ect.
to the op: LSA IS a number you can use. just like lift, duration, ect.
and to the original question. it literally all depends on application, majorly boost vs normally aspirated.
usually more duration = more overlap, bad for boost, good for n/a. and vise versa.
big healthy cams, but like has already been said, theyre hard on parts.
think of 2 cams, both have .600" lift, both have 112lsa, both have all the same specs, except for duration.
which cam will have lobes that are more "peaky" or "severe"???
the cam with more duration
alot of what you are asking has to do with dynamic compression.
Last edited by Bobsmyuncle; 11-11-2010 at 06:58 AM.
11-11-2010, 10:08 PM
#29
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No, the cams are not regrinds. They are brand new made in house cams. Not spec'd in house, but rather spec'd AND manufactured at the same place. Completely made from scratch.
11-12-2010, 05:57 PM
#30
so ur saying that lsa is just a number, had by other numbers(ve's). like u said, doesnt mean you cant USE that number.
You cant use LSA by itself to determine valve events
and to the original question. it literally all depends on application, majorly boost vs normally aspirated.
what does?
usually more duration = more overlap, bad for boost, good for n/a. and vise versa.
Overly simplified but not incorrect
big healthy cams, but like has already been said, theyre hard on parts.
Can we put a quanitative figure to "big healthy"
think of 2 cams, both have .600" lift, both have 112lsa, both have all the same specs, except for duration.
The real "specs" are the VEs,
which cam will have lobes that are more "peaky" or "severe"???
the cam with more duration
i have no idea what you're talking about?
alot of what you are asking has to do with dynamic compression.
"Dynamic compression" as everyone refers to it only involves the IVC event. He never asked about that?
You cant use LSA by itself to determine valve events
and to the original question. it literally all depends on application, majorly boost vs normally aspirated.
what does?
usually more duration = more overlap, bad for boost, good for n/a. and vise versa.
Overly simplified but not incorrect
big healthy cams, but like has already been said, theyre hard on parts.
Can we put a quanitative figure to "big healthy"
think of 2 cams, both have .600" lift, both have 112lsa, both have all the same specs, except for duration.
The real "specs" are the VEs,
which cam will have lobes that are more "peaky" or "severe"???
the cam with more duration
i have no idea what you're talking about?
alot of what you are asking has to do with dynamic compression.
"Dynamic compression" as everyone refers to it only involves the IVC event. He never asked about that?
The point here... is post a specific question to get a specific answer. There's nothing "general" or simple about engine operation if you want above average results. Posting this question shows you want to dig deeper, but you're not using the correct set of tools.
11-13-2010, 08:08 PM
#31
TECH Enthusiast
A key thing that should be considered before we jump into the arena of lift is total camshaft profile......
The issue of symmetrical vs asymmetrical lobe will have different characteristics as such a camshaft designed with polynomials.... ie different ramp rates at .100/.200/.300/.400 as such......
Some other things you must examine are the jerk,ramp rate,and how the effects of jerk and ramp rates affect the seats when closing... Not to mention valve stability after the valve is opened or tossed....
So just looking at lift or adding lift to a camshaft lobe without having a cognitive grasp and correlation to the lobe profile will be a moot point and only result in marginal gains and a stressed valvetrain.....
Yes there are times when extra lift will show gains, but before I run a camshaft lobe profile with higher lift, the overall intent must be honestly examined.... Is this a street or strip car? Too many times honest intent is overlooked for max or peak power.....
The other truth is do not sacrifice duration for lift........ duration places more of a role than lift.....
The other stuff on LSA, I will let you read some more on that, I will only lace you up with a little bit.... but to the guy that said narrow LSA will produce less power, I can prove you wrong on that.... One of the number one reasons guys don't run narrow LSA's on LSX cars that are DD is for vaccum issues to work other accesories, and EPA state and federal emmisions test that must be done on these late model cars. Plus this atmosphere or bandwagon of wanting a "smooth idle"...lol.. On a muscle car? ...... The camaros,gto,chevelles,novas,etc.... of the 65-70 would have most of you tree huggers shaking in your drawers...... Able to get race fuel 100-108 oct at your local gas station.......
But I can make the same amount of power with a 108 LSA as I can a 114..... Basically there are just too many varibles to blanket a general rule of thumb for all combinations.....
Bozz
The issue of symmetrical vs asymmetrical lobe will have different characteristics as such a camshaft designed with polynomials.... ie different ramp rates at .100/.200/.300/.400 as such......
Some other things you must examine are the jerk,ramp rate,and how the effects of jerk and ramp rates affect the seats when closing... Not to mention valve stability after the valve is opened or tossed....
So just looking at lift or adding lift to a camshaft lobe without having a cognitive grasp and correlation to the lobe profile will be a moot point and only result in marginal gains and a stressed valvetrain.....
Yes there are times when extra lift will show gains, but before I run a camshaft lobe profile with higher lift, the overall intent must be honestly examined.... Is this a street or strip car? Too many times honest intent is overlooked for max or peak power.....
The other truth is do not sacrifice duration for lift........ duration places more of a role than lift.....
The other stuff on LSA, I will let you read some more on that, I will only lace you up with a little bit.... but to the guy that said narrow LSA will produce less power, I can prove you wrong on that.... One of the number one reasons guys don't run narrow LSA's on LSX cars that are DD is for vaccum issues to work other accesories, and EPA state and federal emmisions test that must be done on these late model cars. Plus this atmosphere or bandwagon of wanting a "smooth idle"...lol.. On a muscle car? ...... The camaros,gto,chevelles,novas,etc.... of the 65-70 would have most of you tree huggers shaking in your drawers...... Able to get race fuel 100-108 oct at your local gas station.......
But I can make the same amount of power with a 108 LSA as I can a 114..... Basically there are just too many varibles to blanket a general rule of thumb for all combinations.....
Bozz
Last edited by bozzhawg; 11-13-2010 at 08:25 PM.
11-13-2010, 09:55 PM
#32
TECH Resident
11-16-2010, 11:42 AM
#33
You should never lower lift of the cam if power is a concern. Maybe for longevity, but it has no benefit, theorycrafted or otherwise.
Even if you are running a cam with higher valve lift then where the head's flow flatlines, you will spend a longer amount of time in that max flow area and make more power.
The only reason I think the low lift/high duration is popular is because:
1. People can run cheap ~100 spring kits and still live on the street.
and
2. Sadly numbers sell, and a lot of people think "Bigger is Better".
Even if you are running a cam with higher valve lift then where the head's flow flatlines, you will spend a longer amount of time in that max flow area and make more power.
The only reason I think the low lift/high duration is popular is because:
1. People can run cheap ~100 spring kits and still live on the street.
and
2. Sadly numbers sell, and a lot of people think "Bigger is Better".
11-16-2010, 01:08 PM
#34
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It's a cam spec that is the result of the VEs, not the other way around. It doesn't say anything by itself, especially without knowing ICL. Overlap area is the important number, which is dictated by duration, lobe intensity (lift), and LSA. The actual centerlines and lobe asymmetry move the overlap event. All of this is relative to the engine combination, otherwise we're just babbling about theory.
I understand ramp rate and how fast a cam comes off the seat. I just want to know how you calculate overlap.
I think the one of the most important numbers that is seldom talked about is low lift cylinder head flow number. I think it would be intresting to see Head flow data at .050 and .150.
11-16-2010, 03:59 PM
#35
To the OP, there is NO advantage to limiting lift if making horsepower is your goal. The amount of lift the engine wants is combo specific. Valve size, rpm range, head design, etc all play a role. Overlap area required has a lot to do with cubes, curtain area, head design, rpm range, etc. LSA is only a number. If you change the heads, you change the camshaft requirements.
The point here... is post a specific question to get a specific answer. There's nothing "general" or simple about engine operation if you want above average results. Posting this question shows you want to dig deeper, but you're not using the correct set of tools.
The point here... is post a specific question to get a specific answer. There's nothing "general" or simple about engine operation if you want above average results. Posting this question shows you want to dig deeper, but you're not using the correct set of tools.
11-16-2010, 05:28 PM
#36
TECH Fanatic
To the OP, there is NO advantage to limiting lift if making horsepower is your goal. The amount of lift the engine wants is combo specific. Valve size, rpm range, head design, etc all play a role. Overlap area required has a lot to do with cubes, curtain area, head design, rpm range, etc. LSA is only a number. If you change the heads, you change the camshaft requirements.
The point here... is post a specific question to get a specific answer. There's nothing "general" or simple about engine operation if you want above average results. Posting this question shows you want to dig deeper, but you're not using the correct set of tools.
The point here... is post a specific question to get a specific answer. There's nothing "general" or simple about engine operation if you want above average results. Posting this question shows you want to dig deeper, but you're not using the correct set of tools.
Unfortunately too many folks want simple answers to very complicated situations like engine performance. It just doesn't work that way.
Even more unfortunately, to really understand the basics of how engines breathe takes some understanding of physics and compressible fluid dynamics. Without a basic grasp of those topics, explaining or understanding valve events (lift duratiion and lobe centerlines, for example) becomes just guessing. Not even educated guessing in way too many cases.
Threads like this bring out interesting technical responses from folks. Some of them would serve themselves better by not posting. Better to keep one's mouth closed than open it and display one's ignorance.
No disrespect to any specific posters intended: Remember that "ignorance" is a lack of understanding, unlike "stupidity", which is a lack of intelligence. There is considerable "lack of understanding" posted in this thread...and some lack of intelligence, unfortuantely.
"Ignorance can be cured...stupidity goes clear to the bone."
But one has to want to learn. Not everyone really wants to learn...many just want affirmation of what they think is "true". That is sad for them because they don't learn.
Back OT for the OP: A long duration, low lift cam's primary advantage is low valvetrain loads throughout the cycle and therefore a way to get very good durability using relatively low cost parts. Think 100,000 or 200,000 mile OEM engines. It would rarely be a good choice for improving torque and power.
Higher lift, with the correct duration for the application, is virtually always better for making more torque and power. This virtually always means more expensive valvetrain components. OEMs go there with hollow stem intake valves or even titanium valves when it is needed to make the power/rpm/durability goals.
In spite of their popularity LSAs (Lobe Centerline Angles) are a physical result of valve events and lobe shapes. They are a dependant variable rather than an independant variable. Ascribing performance changes to LSA changes doesn't really work in too many situations. One needs to look at how all of the valve events change with just a "simple" change of LSA.
FWIW, not everyone realizes that LSA (or LCA) is specified in "camshaft degrees" and all other valve events (duration) are specified in "crankshaft degrees". If that doesn't make sense, you may need more basic knowledge before discussing what does what.
My highly-opinionated $.02
Jon
11-16-2010, 08:05 PM
#37
Your goals and the rest of the combo(not just the heads) will dictate what duration and lift you should run...the only time you sacrifice either is if the valvetrain is not up to par and can't handle the duration or lift that you SHOULD be running.
11-17-2010, 01:08 PM
#38
I have a question and I will be specific.(im still trying to learn) If a cam has lets say cam 1 220/220 .450 and cam 2 220/220 .600 both on a 112 LSA. Which cam has more overlap? Every formula I have seen to calculate overlap includes Duration and LSA not LIFT (Lobe Intensity).
I understand ramp rate and how fast a cam comes off the seat. I just want to know how you calculate overlap.
I think the one of the most important numbers that is seldom talked about is low lift cylinder head flow number. I think it would be intresting to see Head flow data at .050 and .150.
I understand ramp rate and how fast a cam comes off the seat. I just want to know how you calculate overlap.
I think the one of the most important numbers that is seldom talked about is low lift cylinder head flow number. I think it would be intresting to see Head flow data at .050 and .150.
Overlap in degrees = ((Intake Dur + Exhaust Dur)/4 - LSA) x 2
Or...
Overlap in degrees = ((Intake Dur / 2) - ICL) + ((Exhaust Dur / 2) - ECL)
I'll simplify "overlap triangle" for you. Think in terms of a triangle where angle A= Intake intensity, angle B= Exhaust intensity, and side AB= duration. In this case we'll use hydraulic intensity (adv dur - .050 dur). A "quicker" or more intense lobe profile will have a GREATER angle, pushing angle C farther from side AB. A "slower/lazier" profile will have a LESSER angle, and correspondingly smaller area given a fixed overlap duration.
Cam A
Adv 260/260 Lobe lift: .380/.380 LSA: 112+0 advance
.050 220/220
.100 190/190
.200 160/160
Profile B
Adv 260/260 Lobe Lift: .340/.340 LSA: 112+0 advance
.050 230/230
.100 210/210
.200 165/165
We'll give Cam A's lobes an intensity angle of 30 degrees, and Cam B's quicker (off the seat) lobes an intensity angle of 40 degrees. Given 36 degrees of overlap (adv duration) for both cams, I come up with an arbitrary...
Cam A - 186.90
Cam B - 271.94
Cam B might be suited for a more poorly flowing/undervalved/lazy head. Cam A will have less scavenging which might work well if the engine is over valved, or if port velocity is high.
The acceleration and jerk curves of Cam A are probably pretty pronounced around the .100 lift area, but it will softer on the seat assuming you can keep the lifter on the lobe over the nose. Cam B will be harder on the valve seats (maybe bounce) but should be easier to control over the nose. Notice how the whole lobe profile comes into play when looking at spring requirements.
I oversimplified a lot of things, but maybe this will lead to some good basic theory discussion. As Jon pointed out, everyone in this thread is ignorant to some degree. No real problem there, not everyone can be a Sonny Leonard or Kaase... if they stopped questioning and learning, they'd stop winning.
Last edited by Wicked94Z; 11-18-2010 at 06:59 PM.
11-17-2010, 07:54 PM
#39
A lower LSA will give you a narrower, but taller power band. Peakier power. Usually, going lower than 110 will actually reduce performance at all RPM. Comp Cams Thumpr cams can have LSAs as low as 106. This is because those cams run like **** on purpose. Many people directly correlate a poor idle with power and masculinity. Having to run a vacuum pump for less power is a unique calling. Also, you normally don't want to exceed an LSA or 116 or you will again start to lose power at all RPM. So, low LSA gives you more power for less time, and a high LSA gives you less power for longer.
