Advanced Engineering Tech - High duration/low lift VS Low duration/high lift




Johnny-LT1-runner
09-17-2010, 02:17 AM
I've stumbled across a cam maker that happens to make alot of cams with a high duration/low lift(HD/LL) combo.

What would be the advantages/disadvantages of this vs a low duration/high lift(LD/HL) cam like most go with?

And what about a high vs low LSA on them?

And would it have any advantages/disadvantages if used with a stock head vs a ported head?

Ya'll see where I'm going with this, so take it and run.


01ssreda4
09-26-2010, 10:59 PM
Cue Jeopardy theme music.........

Johnny-LT1-runner
09-26-2010, 11:22 PM
And I thought this was the advanced engineering section.


Sharpe
09-27-2010, 03:45 AM
Yep. Pretty dead nowadays.

01ssreda4
09-28-2010, 11:09 PM
I think thats bc a lot of the veterans with some of the years of good experience don't come around as much. The general lack of accurate information on this site is swelling as the younger and younger groups come. And we get older and older :jest:

justoyz2
10-17-2010, 04:47 PM
You want more lift over more duration.....
-more lift and faster duration means more power (quickly)
-this is based on the compression, valve springs etc....
-more duration requires higher revving of your engine along with matching components.

If you look at all cams, every after market cam has way more lift in comparision to duration. Get it in and get it out, means the air pump, pump faster and makes more power.

ZMX
10-31-2010, 10:26 AM
I've stumbled across a cam maker that happens to make alot of cams with a high duration/low lift(HD/LL) combo.

What would be the advantages/disadvantages of this vs a low duration/high lift(LD/HL) cam like most go with?

Lift is simple. It raises torque by a somewhat small amount at all RPM (unless very excessive, in which case low end torque is slightly compromised).

But to understand what lift is best, you must understand a few things.

First, not all lobes are equal. Even if they have the exact same lift and duration, their lobe acceleration rate (ramp up rate), ie how quickly they reach maximum lift, will vary. As is plainly obvious, the sooner a cam reaches a given amount lift, the more power it will make. A big part of how aftermarket cams increase power is through increasing lobe ramp rate.

As I said before, lift ideally increases torque at all RPM. But, that is only to a certain point. Unless the heads and intake both are set up to take advantage of increased lift, then using a higher lift cam won't help anything. Both LS1 and LS6 heads flow only a few more cfm from 500 to 600 lift. Furthermore, an LS6 intake isn't good for much above 250cfm coming from the heads. A fast 92mm intake is good for about 285cfm from the heads.

Both ramp up rate and valve lift wear the valvetrain more quickly. A major problem with high lift, high ramp, cams is that even good double springs wear out in 30,000 miles. Good beehive springs aren't worth much trust beyond 10,000 miles. This is exacerbated by the fact that big cams are often meant to be used at high RPM.

The more significant component of spring wear is lift. By increasing lift, the spring is more fully compressed, and even the best springs will eventually stay bent.


So, the cam manufacturer could be doing a number of things, since they design cams for every marketable purpose. Perhaps the lift was decreased so that ramp up rate could be increased without too unreasonably increasing valvetrain wear. Or, perhaps the manufacturer understands that a stock LS head and intake don't flow extra above .500 and sees no point in it high lift.

.
.
.
.


...as far as duration goes, duration is, in simple terms, how to control where the engine makes its torque. Take two otherwise identical cams (lift, ramp rate, LSA) but with different durations. Induction systems not limiting, it will make a given amount of torque at any RPM, and where that torque happens will depend upon the duration. If the low duration Cam A makes 400ft-lb at 3000 RPM, but begins falling off afterward, and the high duration cam B makes 400ft-lb at 6000 RPM, but had low torque at 3000RPM, which one is better? It's all about what you're trying to do with the vehicle. For racing, all you care about is having POWER in the in the narrow RPM band where you run wide open throttle between gears. For this, Cam B would be best. But, when driving normally, you don't want to have rev your engine high or downshift just to be able to accelerate like you're used to. For this, Cam A would be best.


And what about a high vs low LSA on them?

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 shit 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.

And would it have any advantages/disadvantages if used with a stock head vs a ported head?

Ya'll see where I'm going with this, so take it and run.

A ported head will usually make a cam behave as if it had more duration. By running larger runners in the head, the effect is the same as running higher duration. More air is allowed to flow, but that air is flowing in more slowly. To reach peak torque again, the engine must be revved higher. This means more power, which will win you races but also make your car more of a hassle to drive.

On the other hand, optimizing the flow geometry of your heads, or getting different heads that have better flow geometry (less harsh of an angle, low turbulence, etc) will increase torque at all RPM.

The best way to make an engine is by designing all of the components to match for the intended uses.

Heads and intake manifolds with very good flow geometry are often prohibitively expensive and can be too large to fit under a hood. Heads with monstrous runner volume and cross sectional area can flow air for high RPM torque (and thus high power), but make big compromises on low RPM torque.

You can push a bad induction system (poor intake, heads, and/or exhaust) to squeeze out the the last few drops of top end power by using a monstrous cam, but the engine will never reach its true power potential and will be horrible to drive on the street.



....



As you can see, the choice of what goes into your engine is the age old problem. Everything is a tradeoff. With your engine, you must compromise between: appearance, racing capability, streetability, reliability, operating cost, and purchasing price

JustAnotherLS2
10-31-2010, 01:01 PM
Lift is simple. It raises torque by a somewhat small amount at all RPM (unless very excessive, in which case low end torque is slightly compromised).

But to understand what lift is best, you must understand a few things.

First, not all lobes are equal. Even if they have the exact same lift and duration, their lobe acceleration rate (ramp up rate), ie how quickly they reach maximum lift, will vary. As is plainly obvious, the sooner a cam reaches a given amount lift, the more power it will make. A big part of how aftermarket cams increase power is through increasing lobe ramp rate.

As I said before, lift ideally increases torque at all RPM. But, that is only to a certain point. Unless the heads and intake both are set up to take advantage of increased lift, then using a higher lift cam won't help anything. Both LS1 and LS6 heads flow only a few more cfm from 500 to 600 lift. Furthermore, an LS6 intake isn't good for much above 250cfm coming from the heads. A fast 92mm intake is good for about 285cfm from the heads.

Both ramp up rate and valve lift wear the valvetrain more quickly. A major problem with high lift, high ramp, cams is that even expensive titanium double springs wear out in 30,000 miles. Good beehive springs aren't worth much trust beyond 10,000 miles. This is exacerbated by the fact that big cams are often meant to be used at high RPM.

The more significant component of spring wear is lift. By increasing lift, the spring is more fully compressed, and even titanium will eventually stay bent.


So, the cam manufacturer could be doing a number of things, since they design cams for every marketable purpose. Perhaps the lift was decreased so that ramp up rate could be increased without too unreasonably increasing valvetrain wear. Or, perhaps the manufacturer understands that a stock LS head and intake don't flow extra above .500 and sees no point in it high lift.

.
.
.
.


...as far as duration goes, duration is, in simple terms, how to control where the engine makes its torque. Take two otherwise identical cams (lift, ramp rate, LSA) but with different durations. Induction systems not limiting, it will make a given amount of torque at any RPM, and where that torque happens will depend upon the duration. If the low duration Cam A makes 400ft-lb at 3000 RPM, but begins falling off afterward, and the high duration cam B makes 400ft-lb at 6000 RPM, but had low torque at 3000RPM, which one is better? It's all about what you're trying to do with the vehicle. For racing, all you care about is having POWER in the in the narrow RPM band where you run wide open throttle between gears. For this, Cam B would be best. But, when driving normally, you don't want to have rev your engine high or downshift just to be able to accelerate like you're used to. For this, Cam A would be best.




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 shit 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.



A ported head will usually make a cam behave as if it had more duration. By running larger runners in the head, the effect is the same as running higher duration. More air is allowed to flow, but that air is flowing in more slowly. To reach peak torque again, the engine must be revved higher. This means more power, which will win you races but also make your car more of a hassle to drive.

On the other hand, optimizing the flow geometry of your heads, or getting different heads that have better flow geometry (less harsh of an angle, low turbulence, etc) will increase torque at all RPM.

The best way to make an engine is by designing all of the components to match for the intended uses.

Heads and intake manifolds with very good flow geometry are often prohibitively expensive and can be too large to fit under a hood. Heads with monstrous runner volume and cross sectional area can flow air for high RPM torque (and thus high power), but make big compromises on low RPM torque.

You can push a bad induction system (poor intake, heads, and/or exhaust) to squeeze out the the last few drops of top end power by using a monstrous cam, but the engine will never reach its true power potential and will be horrible to drive on the street.



....



As you can see, the choice of what goes into your engine is the age old problem. Everything is a tradeoff. With your engine, you must compromise between: appearance, racing capability, streetability, reliability, operating cost, and purchasing price

Sticky material.

Johnny-LT1-runner
10-31-2010, 04:50 PM
I agree. The cam maker was making cams like that for valvetrain longevity. Makes sense.

Wicked94Z
10-31-2010, 08:23 PM
Sticky material.

So many INCORRECT blanket statements made in ZMX's post :rolleyes: you've got to be kidding!

I agree. The cam maker was making cams like that for valvetrain longevity. Makes sense.

You have no way of knowing that! There's a lot more to a lobe profile than .050 duration, and lobe lift. Hell there's a lot more to it than adv. and .200 duration as well. You can't generalize a camshaft, no way in hell.

Wicked94Z
10-31-2010, 08:36 PM
Lift is simple. It raises torque by a somewhat small amount at all RPM (unless very excessive, in which case low end torque is slightly compromised).

But to understand what lift is best, you must understand a few things.

First, not all lobes are equal. Even if they have the exact same lift and duration, their lobe acceleration rate (ramp up rate), ie how quickly they reach maximum lift, will vary. As is plainly obvious, the sooner a cam reaches a given amount lift, the more power it will make. A big part of how aftermarket cams increase power is through increasing lobe ramp rate.

As I said before, lift ideally increases torque at all RPM. But, that is only to a certain point. Unless the heads and intake both are set up to take advantage of increased lift, then using a higher lift cam won't help anything. Both LS1 and LS6 heads flow only a few more cfm from 500 to 600 lift. Furthermore, an LS6 intake isn't good for much above 250cfm coming from the heads. A fast 92mm intake is good for about 285cfm from the heads.

Your motors run at 28" of depression?

Both ramp up rate and valve lift wear the valvetrain more quickly. A major problem with high lift, high ramp, cams is that even expensive titanium double springs wear out in 30,000 miles. Good beehive springs aren't worth much trust beyond 10,000 miles. This is exacerbated by the fact that big cams are often meant to be used at high RPM.

The more significant component of spring wear is lift. By increasing lift, the spring is more fully compressed, and even titanium will eventually stay bent.

Titanium springs? Really?


So, the cam manufacturer could be doing a number of things, since they design cams for every marketable purpose. Perhaps the lift was decreased so that ramp up rate could be increased without too unreasonably increasing valvetrain wear. Or, perhaps the manufacturer understands that a stock LS head and intake don't flow extra above .500 and sees no point in it high lift.

Increase duration, and decrease lobe lift... what does that do to the nose profile of the lobe?

.
.
.
.


...as far as duration goes, duration is, in simple terms, how to control where the engine makes its torque. Take two otherwise identical cams (lift, ramp rate, LSA) but with different durations. Induction systems not limiting, it will make a given amount of torque at any RPM, and where that torque happens will depend upon the duration. If the low duration Cam A makes 400ft-lb at 3000 RPM, but begins falling off afterward, and the high duration cam B makes 400ft-lb at 6000 RPM, but had low torque at 3000RPM, which one is better? It's all about what you're trying to do with the vehicle. For racing, all you care about is having POWER in the in the narrow RPM band where you run wide open throttle between gears. For this, Cam B would be best. But, when driving normally, you don't want to have rev your engine high or downshift just to be able to accelerate like you're used to. For this, Cam A would be best.




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 shit 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.

You haven't seen the specs of an actual pro stock, or super stock cam have you? :jest:


A ported head will usually make a cam behave as if it had more duration. By running larger runners in the head, the effect is the same as running higher duration. More air is allowed to flow, but that air is flowing in more slowly. To reach peak torque again, the engine must be revved higher. This means more power, which will win you races but also make your car more of a hassle to drive.

On the other hand, optimizing the flow geometry of your heads, or getting different heads that have better flow geometry (less harsh of an angle, low turbulence, etc) will increase torque at all RPM.

Oh, please tell how I can optimize the flow geometry of my heads :confused:

The best way to make an engine is by designing all of the components to match for the intended uses.

Heads and intake manifolds with very good flow geometry are often prohibitively expensive and can be too large to fit under a hood. Heads with monstrous runner volume and cross sectional area can flow air for high RPM torque (and thus high power), but make big compromises on low RPM torque.

While we're making generalized blanket statements... Better tell that to the LS3/L92 head designers :rolleyes:

You can push a bad induction system (poor intake, heads, and/or exhaust) to squeeze out the the last few drops of top end power by using a monstrous cam, but the engine will never reach its true power potential and will be horrible to drive on the street.



....



As you can see, the choice of what goes into your engine is the age old problem. Everything is a tradeoff. With your engine, you must compromise between: appearance, racing capability, streetability, reliability, operating cost, and purchasing price

I just scratched the surface, I'll wait for your responses...

Johnny-LT1-runner
11-01-2010, 02:43 AM
So many INCORRECT blanket statements made in ZMX's post :rolleyes: you've got to be kidding!



You have no way of knowing that! There's a lot more to a lobe profile than .050 duration, and lobe lift. Hell there's a lot more to it than adv. and .200 duration as well. You can't generalize a camshaft, no way in hell.

And the asshole raises it's ugly head. :gtfo:

That is what the cam maker told me, so I'll take their word for it. Please don't post in this thread if you're gonna make bullshit fucking posts like all the others.

01ssreda4
11-01-2010, 04:34 AM
:werd: johnny

:jest:

ZMX
11-01-2010, 09:13 AM
blanket statements

You have no way of knowing that! There's a lot more to a lobe profile than .050 duration, and lobe lift. Hell there's a lot more to it than adv. and .200 duration as well. You can't generalize a camshaft, no way in hell.

Basic writing 101: Know your audience. I'm not talking to engineers. The OP is clearly speaking from a limited knowledge base. You couldn't possibly begin to expect him or anyone else to learn anything without at least a basic foundation.

Your motors run at 28" of depression? Nope. Again, I'm talking in basic terms here. Your knowledge of head flow specs measured at 28 inches of water and intake manifolds typically measured at 1.5 inches of mercury has been flaunted (have a cookie) because you fail to realize what I'm saying. And, quite simply, it's that heads measured at 28 inches to flow 250cfm will max out an LS6 intake.

Titanium springs? Really?No. Typo. I was thinking of titanium retainers.

Increase duration, and decrease lobe lift... what does that do to the nose profile of the lobe? Makes it longer and flatter. If you have an actual point, feel free to make it.

You haven't seen the specs of an actual pro stock, or super stock cam have you? *yawn* I have. But again, English 101. You think anyone running an extreme setup that my basic guidelines don't apply to will be reading my posts for help in the first place?

Oh, please tell how I can optimize the flow geometry of my heads
http://www.dartheads.com/products/cylinder-heads/small-block-chevy-aluminum-heads/18-race-series-small-block-chevy-cylinder-heads.html
http://www.dartheads.com/products/cylinder-heads/small-block-chevy-aluminum-heads/9-race-series-small-block-chevy-cylinder-head.html


While we're making generalized blanket statements... Better tell that to the LS3/L92 head designers
I forgot LS3 heads had 285cc intake runners.

Wicked94Z
11-01-2010, 05:55 PM
this thread is insulting to "advanced tech"

Johnny-LT1-runner
11-02-2010, 02:16 AM
this thread is insulting to "advanced tech"

Your posts are insulting to all threads and users. At least try to add some valid info instead of bringing everything down. :bang:

01ssreda4
11-02-2010, 03:26 AM
Obviously a toolbag and a douche. Kinda reminds me of Rich on Pinks :nod:

Ethan[ws6]
11-02-2010, 05:30 PM
this thread is insulting to "advanced tech"

You're an idiot.. ZMX just owned you in every way possible. Feel free to stop posting here. OP the only info I can give you at this point is... listen to what ZMX said. He pretty much covered everything. lol.

Wicked94Z
11-02-2010, 06:10 PM
Sorry this is the advanced tech section, not the teenagers trying to understand basic camshaft design section. The OP's question is WAY too general, which prompted the general response from ZMX that doesn't contain any real tangible information. That's why I said this thread was insulting to this section. Now...

Limiting lobe lift *CAN* result in a tamer nose profile, but it can also result in a more VIOLENT profile as well. If the OP cared to post an example up I could give him some guidance on the intended application.

LSA is just a number, it falls where it does based on the VEs. To say "XXX" LSA will result in poor performance is silly. A specific engine combination needs a specific set of VEs. OP... I posted ALOT of good information in your other threads, which you ignored, claiming you already knew it. Yet here we are asking the same basic questions... :confused:

Stock heads will want a different cam than ported heads, even to operate in the same RPM range on the same cubes/compression. Again, post an example and you'll get a more detailed response.

Ethan[ws6]
11-02-2010, 06:37 PM
Yeah.. more aggressive or in your words, VIOLENT lobe profile isn't going to be as good on the engine components, but that is a compromise made to gain power.

Yeah LSA is just a number... a number that we use as a reference to valve events.. and it is a good reference at that.. If it is so silly, how come you are the only person in the world that seems to think so?

Wicked94Z
11-02-2010, 08:02 PM
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.

Ethan[ws6]
11-02-2010, 08:29 PM
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.

ZMX
11-03-2010, 02:21 AM
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.

Ethan[ws6]
11-03-2010, 11:20 AM
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)

Johnny-LT1-runner
11-05-2010, 03:03 AM
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.

01ssreda4
11-05-2010, 03:19 AM
Johnny I'm afraid you are asking for a miracle. Leave this one to the delete Gods.........

Bobsmyuncle
11-11-2010, 03:08 AM
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.

garygnu
11-11-2010, 08:41 PM
to the Op maybe the cam maybe a stock cam reground.custom cams cost $25 over a shelf cam and you get what you need.there are alot of cons bs people stick with the proven .

01ssreda4
11-11-2010, 10:08 PM
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.

Wicked94Z
11-12-2010, 05:57 PM
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" :confused:

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?


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.

bozzhawg
11-13-2010, 08:08 PM
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

rsz288
11-13-2010, 09:55 PM
The other truth is do not sacrifice duration for lift........ duration places more of a role than lift.....



i.e. GM HOT cam?

Puck
11-16-2010, 11:42 AM
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".

WS6RED2002TA
11-16-2010, 01:08 PM
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 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.

Bobsmyuncle
11-16-2010, 03:59 PM
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.

you have takin this thread so far off fuckin topic its pointless for u to post anything. plz stfu

Old SStroker
11-16-2010, 05:28 PM
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.

Well said, Wicked, and important to this thread, IMO.

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

Puck
11-16-2010, 08:05 PM
The other truth is do not sacrifice duration for lift........ duration places more of a role than lift.....

Why should you ever sacrifice one for the other?

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.

Wicked94Z
11-17-2010, 01:08 PM
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.

If LSA is known....

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.

WKMCD
11-17-2010, 07:54 PM
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 shit 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.


You might want to rethink this....:bang:

bozzhawg
11-19-2010, 10:18 PM
You might want to rethink this....:bang:

x2..............

wrd1972
12-28-2010, 01:34 PM
:bigun2:

Uh...Make that
:corn: