i need a better understanding of how ....... (long)

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01-29-2003, 03:08 PM

#21

HITMANSS

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Re: i need a better understanding of how ....... (long)

So long as this conversation stays civilized, I'm all for continuing the dialogue. First let's take Dean's comments:

Dean, you asked for examples of factual errors that, IMO, you made. Here's a few:

"Lobe Sep Angle is the difference in degrees between the two lobe peaks. Duration, ramp rates, and intake centerline all determine where the respective peaks occur with respect to piston timing."

This is factually incorrect. The cam duration and the ramp rates have no effect whatsoever on where the lobe peaks are. They do however, affect valve events with respect to piston timing. That may have been what you were trying to say.

The intake centerline, on the other hand, does affect where the lobe peaks are in relation to piston timing. That part is correct. This is the definition of intake centerline per Comp Cams:

"The intake centerline is the position of the centerline, or peak lift point, of the intake lobe in relation to top dead center of the piston. This can be changed by "degreeing" the cam into the engine."

You agree, or not?

Here's another example:

"Now it should be clear that you can change the LSA in one of several ways..."

Again, this is factually incorrect. You can make the LSA narrower, or wider --- those are your only choices. That angle is ground into the cam, and can never be changed. Never.

What you can do is to change the intake centerline to make ALL the valve events occur earlier or later with respect to TDC, by advancing or retarding the cam.

Again, maybe this is what you meant to say.

Now, last point. I absolutely do think that LSA is a simple concept to grasp, but I never said or implied that it would always have a certain effect. The observations I made about the effect of LSA on idle & performance were intended tobe specific to LS1's, not as global truths.

NOw, let's turn the tables. Please point out to me any statement that I have made that is factually incorrect, and back it up. If I'm wrong, I'll admit it, but I want to see the goods.

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01-29-2003, 03:35 PM

#22

HITMANSS

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Re: i need a better understanding of how ....... (long)

Now, for Chris's comments. You're a Director, and may know far more than I about some things. But that doesn't mean you're right on this subject.

We disagree about the effect of LSA on power peak. This is not a semantic disagreement at all. I stand by my opinion as stated, that widening the LSA will result in lower peak HP at lower RPM. I have a dyno study to back me up, from a well known performance mag. I have also seen the dyno comparisons between the MTI T1 & B1 cams. What is the factual basis for your opinion?

We disagree about the LSA being a "metric" in itself that can be "manipulated" to achieve a certain power level. It is definitely a "metric" --- just try ordering a cam without it! An it is certainly a meaningful way to adjust the power band to a given RPM band --- tuners have been doing this forever.

BTW, we also disagree about whether lobe selection can affect valve timing. Let's say we have two cams: one is a 224/224 .550 114 on XE lobes, and the other is a 224/224 .581 114 on XE-R lobes. They both have the same centerline. Now how are the valve timing events different? The intakes and exhaust with both open and close at exactly the same times. The difference is that the XE-R lobe cam will have higher lift #'s @ .006" and at .050".

Or perhaps this is what you were trying to say, and meant by "valve timing".

Thanks, Chris for pointing out those areas where we did agree. I'm sure if we had a few hours and a few 6-packs, we could reach 100% agreement! <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

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01-29-2003, 06:01 PM

#23

ChrisB

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Re: i need a better understanding of how ....... (long)

<blockquote>quote:<hr />Originally posted by HITMANSS:

"Now it should be clear that you can change the LSA in one of several ways..."

Again, this is factually incorrect. You can make the LSA narrower, or wider --- those are your only choices. That angle is ground into the cam, and can never be changed. Never.
<hr /></blockquote>

I am sure the point was that, not specifying the LSA itself, several things can effect it. Let's take a given camshaft. Now change the intake lobe. Depending on the profile of the lobe the intake lobe peak may very well occur at a different place. You can also advance or retard the camshaft. And you can alter your ivo events, which, with a given lobe, will change your intake centerline - and thus your lsa (assuming everything else is constant.

<blockquote>quote:<hr />
NOw, let's turn the tables. Please point out to me any statement that I have made that is factually incorrect, and back it up. If I'm wrong, I'll admit it, but I want to see the goods. <hr /></blockquote>You haven't said anything incorrect per se - what I tried to point out originally is that you are using a different abstract model to view a camshaft setup. The assumptions that make comparisons based on lsa valid only hold so far as the lobes are the same/similar. Once you start altering lobes/advance/retard, other factors effect the valve timing, and thus may enhance or mitigate the "effects of lsa alteration".
You can have two different models, and within their context's neither are factually incorrect - but you have to understand the limitations and underlying assumptions of your model also.

<blockquote>quote:<hr />Now, for Chris's comments. You're a Director, and may know far more than I about some things. But that doesn't mean you're right on this subject. <hr /></blockquote>

I don't think I ever said or implied that. But since your brought it up, conversely, it doesn't mean that I am incorrect (as your statement implies).

<blockquote>quote:<hr />We disagree about the effect of LSA on power peak. This is not a semantic disagreement at all. I stand by my opinion as stated, that widening the LSA will result in lower peak HP at lower RPM. I have a dyno study to back me up, from a well known performance mag. I have also seen the dyno comparisons between the MTI T1 & B1 cams. What is the factual basis for your opinion?<hr /></blockquote>

I will argue this a couple of different ways

1) I have never seen/heard any study that indicates a wider lsa (everything else the same) will *LOWER* the rpm peak (again, we are assuming norms here - ls1/sbc/lt1, etc. - not some strange/exotic engine, power adder setup, etc.) But a negative affirmation like that is of course non-conclusive. I would be interested to see your studies/dyno-graphs that indicate the opposite. Please ensure that lobe choice/advance, etc. are the same (lsa is the only variable). I believe there were some early b1/t1 dyno graphs like this, but I do not have them.

2) Look at your own comments. I believe you indicated that a wider lsa will result in a broader torque curve - this means it peaks later (ipso facto). If the torque curve peaks later and is generally flatter it *will* have a higher rpm hp peak.

3) What does LSA effect? Obviously overlap, and at first it is tempting to say you need more overlap at higher rpm (because everyone associates high rpm power with a big nasty camshaft, etc.). So lets say we take a 221/221 112+4 camshaft and a 221/221 114+4 camshaft.

As we go higher in the RPM range and engine does require slightly more overlap - simply because the actual flow time per unit degree is decreased. BUT there are other factors also - as in the example above - Our 112 camshaft will have an intake centerline of 108 - but our 114 camshaft will have an intake centerline of 110.

So even though we have reduced overlap slightly, we have also just effectively retarded our intake lobe (which is going to be a primary RPM determinate) - and in practice that is a much bigger component of rpm than the smaller reduction in overlap - though there are specific instances where one definitely could be more important than the other (which goes on to prove that LSA alone is not enough information).

Now we could have maintained a constant intake centerline at 108, but then the 221/221 114 cam would be advanced 6 degrees, so you are now altering both he lsa and the advance - and of course "advancing" a cam will reduce the rpm range (or advancing the intake lobe in this case).

Now if we look at valve events we could estimate an IVO of around 3 BTDC, and an IVC of around 39 ABDC for the 112+4 cam. The 114+4 cam would give us closer to a 1BTDC opening/41ABDC closing. The IVC number is going to be a very important number with respect to rpm range - we are closing the cam well into the power stroke - so the piston is actually working against the cylinder filling - yet it is the inertia of the air that continues to fill the cylinder (why high velocity ports are good). The higher the rpm the higher the inertia of the air column - also, as flow is a function of time, while the valve events are a function of rotational degrees, as rpm goes up the actual "flow time" that the 4x degrees ABDC represent lessens - so as this number gets larger, the rpm range of the camshaft itself increases.

The point is, looking at the valve events alone we can come up with a good idea of how two cams compare (though we still would like other information, such as lobe profile, etc.) - but LSA itself can not be independently manipulated, even when the lobes are the same. And I could easily leave the lsa exactly the same, yet alter the lobes/advance to totally change the characteristics of the camshaft. This would be reflected in the valve events, but not the lsa value itself.

<blockquote>quote:<hr />BTW, we also disagree about whether lobe selection can affect valve timing. Let's say we have two cams: one is a 224/224 .550 114 on XE lobes, and the other is a 224/224 .581 114 on XE-R lobes. They both have the same centerline. Now how are the valve timing events different? The intakes and exhaust with both open and close at exactly the same times. The difference is that the XE-R lobe cam will have higher lift #'s @ .006" and at .050".
<hr /></blockquote>

The 224 numbers are a reflection of how long the valve is open at 0.050" of tappet lift. The valve events themselves are going to be a function of total duration. You have to remember the these "specs" are only a snapshot of one portion of a continuous profile. The XE-R lobes achieve the extra lift by being more aggressive - *assuming* they are more aggressive across the entire duration, they will have a SMALLER advertised duration, and this a SMALLER spread between the valve events for a given lobe. Conversely a uniformly quicker lobe profile will give a larger value for duration @ 0.200 than a slower profile with the same 0.050" duration.

If you grind a cam with smaller total duration on the same lsa/IC then you will end up with different valve events.

<blockquote>quote:<hr />Or perhaps this is what you were trying to say, and meant by "valve timing".<hr /></blockquote>

No, I meant exactly what I said.

Chris Bennight

[ January 29, 2003, 06:03 PM: Message edited by: ChrisB ]

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01-29-2003, 06:59 PM

#24

HITMANSS

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Re: i need a better understanding of how ....... (long)

Chris, maybe we're getting somewhere. At least you acknowledge, that in your opinion, I haven't said anything that is incorrect, per se. That's more than I've gotten out of Dean. I appreciate the lack of flames.

The abstract model that I've been using is what most cam manufacturers use. When you order a cam, you order the duration, lift, LSA, & advance. Very few guys order a cam by specifying the valve timing events, & just let the LSA work out to whatever.

The dyno study I referred to was published in a recent version of Car Craft magazine, entitled "What's the Angle?" It's been widely discussed on several UBBs. The article compared dyno results for 3 identical SBC cams w/ LSA's of 106, 110, & 114. The 110 & 114 cams peaked at the same RPM, but the 106 peaked 300 RPMs higher. I'll try to find a link.

You're correct that I stated that a wider LSA will result in a broader torque curve, but it does not necessarily follow that the peak will occur at a higher RPM. IMO, the torque curve will be broader on either end --- below 2K RPMs & above the peak at which peak HP occurs. Everything in between will be slightly lower. Think about it --- if you could get a broader torque curve AND higher peaks, why woudn't everyone run wide LSA's The answer is that you can't have your cake & eat it too --- there's a tradeoff. Narrow LSA = narrower, peakier power band.

Tell ya what --- let's just agree to disagree. I'm always receptive to new data, so if you can find some dyno results that contradict me, please post them. I'm going to be dynoing this weekend w/a bunch of EFA guys, & maybe there will be some comparisons to be done then. Lord knows there are tons of cams out there w/ the same specs, but different LSA's (112 & 114).

Cheers,

Gary

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01-29-2003, 07:52 PM

#25

ChrisB

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Re: i need a better understanding of how ....... (long)

<blockquote>quote:<hr />The abstract model that I've been using is what most cam manufacturers use. When you order a cam, you order the duration, lift, LSA, & advance. Very few guys order a cam by specifying the valve timing events, & just let the LSA work out to whatever. <hr /></blockquote>

If you look at your cam card it *always* contains the valve events. THOSE are what people use when a cam is custom designed for your application - the lsa, advance, etc. is going to be a function of the valve events that are required for your setup - not vice versa. Aside from that - the fact that it is a simple or common way to express something does not make it correct.

<blockquote>quote:<hr />The dyno study I referred to was published in a recent version of Car Craft magazine, entitled "What's the Angle?" It's been widely discussed on several UBBs. The article compared dyno results for 3 identical SBC cams w/ LSA's of 106, 110, & 114. The 110 & 114 cams peaked at the same RPM, but the 106 peaked 300 RPMs higher. I'll try to find a link.
<hr /></blockquote>

If you could find a link or scan it I would definitely be interested. Even having not seen it I can guarauntee that LSA is not the only variable - as I illustrated above either the intake or exhaust centerline is also going to be altered - right there is one of the problems with just looking at LSA - you can't effectively isolate it, period.

<blockquote>quote:<hr />You're correct that I stated that a wider LSA will result in a broader torque curve, but it does not necessarily follow that the peak will occur at a higher RPM. IMO, the torque curve will be broader on either end --- below 2K RPMs & above the peak at which peak HP occurs. Everything in between will be slightly lower. Think about it --- if you could get a broader torque curve AND higher peaks, why woudn't everyone run wide LSA's The answer is that you can't have your cake & eat it too --- there's a tradeoff. Narrow LSA = narrower, peakier power band.<hr /></blockquote>

Yes, you can "broaden it" by flattening out the bottom end also, agreed. I never said you would neccecarily get higher in magnitue peaks - only that they would likely be at a higher rpm.
And in actuality, what happens depends on to many other variables - you could easily gain or loose power - it depends on your port cross sectional area, volume, operating range, head flow characteristics, motor size, etc. The fact is a LSA widening on one engine may very well make more power/torque across the board, while on another engine it would loose.
But I will agree will stipulate this, as it is irrelevant - I think there are to many other variables to say in every situation what a lsa change is going to do - it also depends on the absolutes - e.g. going narrower may be fine at 116 to 112, but the same observations will not hold going from say 102 to 98lsa.

I would instead focus on the valve event issue above - it is the viewpoint that dean purported and accurately conveyed, which you claimed/implied was incorrect.

I think what you are missing here is the point everyone is trying to make - it's not that your saying anything factually incorrect *FOR A GIVEN CONTEXT* - it's that the generalizations you make to determine characteristics based on lsa, etc.
The problem is, by the nature of how LSA is determined, it CAN NOT be isolated alone - when you alter lsa you will alter either the IC or EC also - effectively advancing/retarding lobes.

The advantage of looking at valve timing is that you *can* isolate each event - and each event has a conceptualized effect.

You *can't* explain how LSA has any effect on the motor without talking about valve events themselves. LSA is simply a byproduct of them. Not that it isn't usefull or convienent - it is, or it wouldn't be used - but LSA by itself tells us nothing. Just because a cam is on a 114 lsa doesn't mean it is a good blower cam, will have a good idle, etc. - likewise just because a cam is on a 110 doesn't mean it will idle rough but make good power/torque.

Since you dropped the issue I assume you now see the point regarding other factors besides lsa effecting valve events (e.g. how different lobes, even ones with identical duration @ 0.05, etc. can effect valve events).

I would also challenge you to provide a logical conceptualized description of the effect of lsa, and/or contradict what I posted above.

Chris Bennight

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01-30-2003, 07:25 AM

#26

HITMANSS

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Re: i need a better understanding of how ....... (long)

In a previous post, I stated that lobe selection had no effect on valve timing events, and gave as an example a typical 224/224 cam. You correctly pointed out that the 224 duration is @ .050" lift, but then went on to say that "the valve events themselves are going to be a function of total duration." But in the previous paragraph you had discussed valve timing events, and cited them @.050" lift (3 degrees BTDC).

So which is it???? Let's compare apples to apples here.

The valve timing event #'s I've seen are at .050" lift. I'll stick by what I said.

Re the abstract model, maybe the way I order a custom cam is incorrect, but somehow the cam manufacturer always knows exactly what I want. In addition to valve timing events, the cam card always shows the LSA, even if it's "trivial".

The article was published in the November 2002 issue of Car Craft. Unfortunately it's not shown on their website. The cams in question were (in Car Craft's words) "three otherwise identical Lunati cams". The grind # is H230-235, w/ 230/235 duration @ .050", 280/285 gross duration, .489"/.507" lift. As you pointed out, it's impossible for the LSA to be the only variable, and obvious that the valve timing events are different --- otherwise the cams would be identical.

Perhaps you are correct, and it's impossible to make any generalizations about LSA. I suppose Car Craft could be blowing smoke, and all the threads that I've seen discussing this issue are meaningless. Have it your way.

I'm not sure what I dropped, but I hope you don't mind if I get a few hours sleep in between posts! <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

If you would like to read a logical conceptualized description of the effect of LSA, I suggest you read the article. If I can get my scanner to work under Windows XP, I'll scan it & post it.

Meanwhile, if you can find any dyno charts that support your statements, I'd like to see them. However, since you have already pointed out that it's impossible to isolate LSA, maybe that's pointless too.

Cheers,

Gary

[ January 30, 2003, 01:42 PM: Message edited by: HITMANSS ]

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01-30-2003, 02:28 PM

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Dean98TA

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Re: i need a better understanding of how ....... (long)

After taking a day off to simmer myself down, I see that Hitman is willing to take a more civil approach, so I will do likewise. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

<blockquote>quote:<hr />The cam duration and the ramp rates have no effect whatsoever on where the lobe peaks are. They do however, affect valve events with respect to piston timing. That may have been what you were trying to say.<hr /></blockquote>Yes, from the beginning, I have been trying to relate the cam profile to valve timing events, especially when you are considering valve overlap. Large durations and ramp rates can affect how close the LSA will be if you are trying to control valve overlap. Again, looking at the cam profile on CC's website, you can see that if that cam's duration were larger using the same ramp rates, valve overlap would increase, and if that was undesired, then you would need to either increase the LSA or make the ramp rates more aggressive.

<blockquote>quote:<hr />"The intake centerline is the position of the centerline, or peak lift point, of the intake lobe in relation to top dead center of the piston. This can be changed by "degreeing" the cam into the engine."

You agree, or not?<hr /></blockquote>Totally agree, and I think I even mentioned that if you maintain a specific centerline, then widening the LSA results in changing the exhaust timing in a previous post.

<blockquote>quote:<hr />Again, this is factually incorrect. You can make the LSA narrower, or wider --- those are your only choices. That angle is ground into the cam, and can never be changed. Never.<hr /></blockquote>I believe you missed my point. Yes, the LSA is getting just wider or narrower, but again, looking at it with respect to valve timing, changing the LSA can result, depending on how you degree the cam, in either changing exhaust timing alone, intake timing alone, or both. The latter two means you are changing the intake centerline by degreeing the cam. If it sounded like I was implying that you can change the LSA after it is ground into the cam, I apologize.

Perhaps my effort to keep the discussion basic to prevent information overload had the adverse effect of some information being omitted or being unclear, but hopefully, I've helped clear up the intent of my posts.

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01-30-2003, 04:54 PM

#28

ChrisB

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Re: i need a better understanding of how ....... (long)

<blockquote>quote:<hr />Originally posted by HITMANSS:
 But in the previous paragraph you had discussed valve timing events, and cited them @.050" lift (3 degrees BTDC). So which is it???? Let's compare apples to apples here.
<hr /></blockquote>

I just picked some random numbers that were semi-reasonable to demonstrate the effect of changing LSA, etc. on the valve timing. NO WHERE did I claim that valve events where based on the duratin @0.050" numbers, and infact pointed out that they could be totally different with different lobes.

<blockquote>quote:<hr />
The valve timing event #'s I've seen are at .050" lift. I'll stick by what I said.
<hr /></blockquote>

You can definitely list valve timing @ any lift duration you want, but valve events are when the intake valve opens and closes. I will agree with you - if you list the valve timing events for 0.05" duration then yes, 2 cams with the same 0.050" specs will have the same valve events - AT that duration. That's kinda an ipso facto situation - it's just basically restating the same thing in a different way?

Again, I think you are getting caught up in semantics - the point is the numbers are only a small part of the equation - and because of that when lobes change, etc. lsa comparisons are no longer valid (As valid)

<blockquote>quote:<hr />
Re the abstract model, maybe the way I order a custom cam is incorrect, but somehow the cam manufacturer always knows exactly what I want.
<hr /></blockquote>

I can call up comp and say I want a 306 for a LT1. They will know exactly what I am talking about - but that doesn't mean my description allows for valid comparisons. No one has said that you can't specify a cam using lobes, lsa, advance - you most certainly can.
The basic argument is that looking at valve events is a superior/better way of examining a camshaft - and conversely, looking at lsa as an independent metric is not valid/as valid.

<blockquote>quote:<hr /> As you pointed out, it's impossible for the LSA to be the only variable, and obvious that the valve timing events are different --- otherwise the cams would be identical.
<hr /></blockquote>

Exactly - you can start looking at LSA, intake centerline, exhaust centerline, etc. - but then how do you judge which effect is predomenant? And your comparisons are already not based solely on LSA. On the other hand I am sure we can look at the valve events for the above camshafts and explain the different dynographs.

<blockquote>quote:<hr />
Perhaps you are correct, and it's impossible to make any generalizations about LSA. I suppose Car Craft could be blowing smoke, and all the threads that I've seen discussing this issue are meaningless. Have it your way.<hr /></blockquote>

It is impossible to isolate LSA, so any generalizations you make will be for LSA plus some other factor (advancing/retarding the intake/exhaust lobes). That's a simple fact, and there really isn't any way to argue with that.

Now can you still make generalizations? Yes, of course - but you have to specify the circumstances for which they are valid. If we maintain a certain exhaust centerline, intake centerline, etc. And once we change lobes *many* other factors have changed also. The point is the more you cange the above factors, the less valid those generalizations are - and that is something that needs to be recognized, or your conclusions are invalid.

Anyway, to sum it up my main issue is how you disregard valve events and say that dean doesn't know what he is talking about when he mentions them, etc. I think I have demonstrated above why LSA isn't really a valid comparison tool, as other factors are altered by it - and not always in the same manner.

Chris Bennight

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01-31-2003, 11:31 AM

#29

Dean98TA

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Re: i need a better understanding of how ....... (long)

I did a quickie search on the web and found this to be very interesting reading.

Chevy High Performance Cam article

It echoes what Chris and I have been trying to get across. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

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