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High duration/low lift VS Low duration/high lift

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Old 09-17-2010, 02:17 AM   #1
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Default High duration/low lift VS Low duration/high lift

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.
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Old 09-26-2010, 10:59 PM   #2
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Cue Jeopardy theme music.........
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Old 09-26-2010, 11:22 PM   #3
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And I thought this was the advanced engineering section.
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Old 09-27-2010, 03:45 AM   #4
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Yep. Pretty dead nowadays.
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Old 09-28-2010, 11:09 PM   #5
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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
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Old 10-17-2010, 04:47 PM   #6
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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.
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Old 10-31-2010, 10:26 AM   #7
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Originally Posted by Johnny-LT1-runner View Post
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 chosen based on how well the head flows at various lift levels. More makes more power, and doesn't really have a powerband compromise, so long as it's tuned with duration.

Duration is a catch-all term for the separation of valve events. It doesn't tell the whole story, but more generally means a tradeoff of more high-RPM performance for less low-RPM performance. LSA, combined with duration, gives an idea of valve overlap, which is part of the compromise between drivability and full-throttle power.

Not all lobes are equal. Even if two cams have the same lift and duration, their lobe acceleration rate (ramp up rate), ie how quickly they reach maximum lift, will vary. The sooner a cam reaches a given amount lift, the more power it will make. A big part of how aftermarket cams increase power without sacrificing the powerband is through increasing lobe ramp rate.

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 quickly. Rocker arms and pushrods are also strained heavily and must be upgraded to keep from outright breaking, or simply to maintain a stable valvetrain without valve-float.

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 it won't make as much power as it could, and be horrible to drive on the street.

....


Everything is a tradeoff. With your engine, you must compromise between: appearance, racing capability, streetability, reliability, operating cost, and purchasing price

Last edited by ZMX; 12-16-2014 at 01:04 AM.. Reason: Trying to fix old garbage.
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Old 10-31-2010, 01:01 PM   #8
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Originally Posted by ZMX View Post
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 **** 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.
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Old 10-31-2010, 04:50 PM   #9
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I agree. The cam maker was making cams like that for valvetrain longevity. Makes sense.
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Old 10-31-2010, 08:23 PM   #10
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Quote:
Originally Posted by JustAnotherLS2 View Post
Sticky material.
So many INCORRECT blanket statements made in ZMX's post you've got to be kidding!

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Originally Posted by Johnny-LT1-runner View Post
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.
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Old 10-31-2010, 08:36 PM   #11
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Quote:
Originally Posted by ZMX View Post
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 **** 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?


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

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

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...
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Old 11-01-2010, 02:43 AM   #12
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So many INCORRECT blanket statements made in ZMX's post 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 ******* raises it's ugly head.

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 ******* posts like all the others.
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Old 11-01-2010, 04:34 AM   #13
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Old 11-01-2010, 09:13 AM   #14
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Originally Posted by Wicked94Z View Post
blanket statements
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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.
True.

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Your motors run at 28" of depression?
Right. "CFM" is not the same in an engine as it is on a flowbench.

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Originally Posted by Wicked94Z View Post
Titanium springs? Really?
No. Typo. I was thinking of titanium retainers.

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Originally Posted by Wicked94Z View Post
Increase duration, and decrease lobe lift... what does that do to the nose profile of the lobe?
Makes it longer and flatter.


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Oh, please tell how I can optimize the flow geometry of my heads
That's part of head porting. Another way is in aftermarket castings with reduced angles.
http://www.dartheads.com/products/cy...der-heads.html
http://www.dartheads.com/products/cy...nder-head.html

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Old 11-01-2010, 05:55 PM   #15
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this thread is insulting to "advanced tech"
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Old 11-02-2010, 02:16 AM   #16
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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.
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Old 11-02-2010, 03:26 AM   #17
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Obviously a toolbag and a douche. Kinda reminds me of Rich on Pinks
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Old 11-02-2010, 05:30 PM   #18
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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.
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Old 11-02-2010, 06:10 PM   #19
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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...

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.
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Old 11-02-2010, 06:37 PM   #20
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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?
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