The facts about LSA on cams
09-26-2002, 09:37 PM
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The facts about LSA on cams There seems to be some misinformation as to where the power range is moved with respect to LSA.
If the LSA is larger(wider), the power range is widened and shifted down.
If the LSA is smaller(narrower), the power range is narrowed and shifted up.
Here is an excerpt from "The Chevrolet Racing Engine" by Bill "Grumpy" Jenkins, to back this up.
LOBE SEPERATION ANGLE
The displacement angle between the lobe centers is an important design parameter. By spreading the lobe centers, the exhaust events will occur earlier relative to the crank position, and the intake events will occur later. This results in less overlap period (exhaust closing and intake opening move closer together). When the centers are moved closer together, all these effects will be reversed. At this point, we have to assume that the reader has some understanding of camshaft functioning so that a detailed discussion of the lobe and event relationships is not necessary. Nonetheless, we may be able to shed some light on what we consider important about these relationships when a camshaft is being ground for a high speed race engine.
Changing the centers will alter the engines characteristics to some extent. If the centers are spread, the engine range is wider, and shifted toward the low end of the scale. Cams used in stock engines with high rev potential are often ground with centers as wide as 114 degrees. In the opposite extreme, when the centers are close together, the range will be reduced and shifted higher in the rpm scale.
Since this also leads to increased overlap, the resultant increase in exhaust scavenging during the overlap may be detrimetnal to the fuel specific curve because raw fuel is drawn across the chamber and out of the exhaust.
This brings us to another important concept related to the valve duration. Of the four valve events, we have strong feelings about only one: the intake closing. This event is universally accepted as the most important paramter, compared to the relative insensitivity that most engines display for precise placement of the other events. This point must be finely balanced to gain the greatest amount of cylinder filling before the valve is closed. We know the intake valve can be closed well afer the piston has passed botton dead center on the intake stroke and is actually moving up on the compression stroke. It takes some time before the upward piston movement initiates backflow into the intake port (if still uncovered). By delaying the closing point, we take advantage of this extra area under the curve for more induction to create more power. Closing it late also takes advantage of of any velocity built up in the intake runner; however, this velocity is a major factor only at high engine speeds. If the valve is closed earlier, there is less blowback lost up the intake, and the pressure begins building more quickly in the cylinder- and important factor for low speed torque.
When selecting the duration and lobe centers, you have to consider the forgoing effects. And you can see how the rod ratio and induction efficiency can have a bearing on optimal intake closing (remember the rod ratio affects pistion accelleration away from BDC and TDC as well as the amount of time the piston resides in the relative BDC and TDC locations).
This location of the intake closing is the effect felt when the cam is advnaced or retarded with respect to the crankshaft. When the cam is advanced the lobes are slightly displaced in the direction of rotation so the events will occur earlier. The intake closing occurs earlier, and the bottn-end performance is enhanced. When the cam is retarded, the lobes are moved in the direction opposte of rotation. The intake closes later, relative to crank (and piston) movement. This results in better breathing at high engine speeds and the consequent power gains the upper range are felt. Normally, this effect cannot be achieved with a change of less than two degrees.
<small>[ September 26, 2002, 11:24 PM: Message edited by: kewlbrz ]</small>
If the LSA is larger(wider), the power range is widened and shifted down.
If the LSA is smaller(narrower), the power range is narrowed and shifted up.
Here is an excerpt from "The Chevrolet Racing Engine" by Bill "Grumpy" Jenkins, to back this up.
LOBE SEPERATION ANGLE
The displacement angle between the lobe centers is an important design parameter. By spreading the lobe centers, the exhaust events will occur earlier relative to the crank position, and the intake events will occur later. This results in less overlap period (exhaust closing and intake opening move closer together). When the centers are moved closer together, all these effects will be reversed. At this point, we have to assume that the reader has some understanding of camshaft functioning so that a detailed discussion of the lobe and event relationships is not necessary. Nonetheless, we may be able to shed some light on what we consider important about these relationships when a camshaft is being ground for a high speed race engine.
Changing the centers will alter the engines characteristics to some extent. If the centers are spread, the engine range is wider, and shifted toward the low end of the scale. Cams used in stock engines with high rev potential are often ground with centers as wide as 114 degrees. In the opposite extreme, when the centers are close together, the range will be reduced and shifted higher in the rpm scale.
Since this also leads to increased overlap, the resultant increase in exhaust scavenging during the overlap may be detrimetnal to the fuel specific curve because raw fuel is drawn across the chamber and out of the exhaust.
This brings us to another important concept related to the valve duration. Of the four valve events, we have strong feelings about only one: the intake closing. This event is universally accepted as the most important paramter, compared to the relative insensitivity that most engines display for precise placement of the other events. This point must be finely balanced to gain the greatest amount of cylinder filling before the valve is closed. We know the intake valve can be closed well afer the piston has passed botton dead center on the intake stroke and is actually moving up on the compression stroke. It takes some time before the upward piston movement initiates backflow into the intake port (if still uncovered). By delaying the closing point, we take advantage of this extra area under the curve for more induction to create more power. Closing it late also takes advantage of of any velocity built up in the intake runner; however, this velocity is a major factor only at high engine speeds. If the valve is closed earlier, there is less blowback lost up the intake, and the pressure begins building more quickly in the cylinder- and important factor for low speed torque.
When selecting the duration and lobe centers, you have to consider the forgoing effects. And you can see how the rod ratio and induction efficiency can have a bearing on optimal intake closing (remember the rod ratio affects pistion accelleration away from BDC and TDC as well as the amount of time the piston resides in the relative BDC and TDC locations).
This location of the intake closing is the effect felt when the cam is advnaced or retarded with respect to the crankshaft. When the cam is advanced the lobes are slightly displaced in the direction of rotation so the events will occur earlier. The intake closing occurs earlier, and the bottn-end performance is enhanced. When the cam is retarded, the lobes are moved in the direction opposte of rotation. The intake closes later, relative to crank (and piston) movement. This results in better breathing at high engine speeds and the consequent power gains the upper range are felt. Normally, this effect cannot be achieved with a change of less than two degrees.
<small>[ September 26, 2002, 11:24 PM: Message edited by: kewlbrz ]</small>
09-26-2002, 10:03 PM
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Re: The facts about LSA on cams Well now I'm confused, <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> cause Comp cams says a lower LSA moves the power peak lower in the rpm range. This is off their website. Here take a look...
The last thing we will discuss is the difference between intake centerline and lobe separation angle. These two terms are often confused. Even though they have very similar names, they are very different and control different events in the engine. Lobe separation angle is simply what it says. It is the number of degrees separating the peak lift point of the exhaust lobe and the peak point of the intake lobe. This is sometimes referred to as the "lobe center" of the cam, but we prefer to call it the lobe separation angle. This can only be changed when the cam is ground. It makes no difference how you degree the cam in the engine, the lobe separation angle is ground into the cam. The intake centerline, on the other hand, 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. Figure 1 shows a normal 270 degree cam. It has a lobe separation of 110°. We show it installed in the engine 4° advanced, or at 106° intake centerline. The light grey curves show the same camshaft installed an additional four degrees advanced, or at 102 degrees intake centerline. You can see how much earlier overlap is taking place and how the intake valve is open a great deal before the piston starts down. This is usually considered as a way to increase bottom end power, but as you can see there is much of the charge pushed out the exhaust, making a less efficient engine. There is a recommended intake centerline installation point on each cam card, and it is important to install the cam at this point. As far as the mechanics of cam degreeing, Competition Cams has produced a simple, comprehensive video (part #190) that will take you step by step through the process.
The last thing we will discuss is the difference between intake centerline and lobe separation angle. These two terms are often confused. Even though they have very similar names, they are very different and control different events in the engine. Lobe separation angle is simply what it says. It is the number of degrees separating the peak lift point of the exhaust lobe and the peak point of the intake lobe. This is sometimes referred to as the "lobe center" of the cam, but we prefer to call it the lobe separation angle. This can only be changed when the cam is ground. It makes no difference how you degree the cam in the engine, the lobe separation angle is ground into the cam. The intake centerline, on the other hand, 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. Figure 1 shows a normal 270 degree cam. It has a lobe separation of 110°. We show it installed in the engine 4° advanced, or at 106° intake centerline. The light grey curves show the same camshaft installed an additional four degrees advanced, or at 102 degrees intake centerline. You can see how much earlier overlap is taking place and how the intake valve is open a great deal before the piston starts down. This is usually considered as a way to increase bottom end power, but as you can see there is much of the charge pushed out the exhaust, making a less efficient engine. There is a recommended intake centerline installation point on each cam card, and it is important to install the cam at this point. As far as the mechanics of cam degreeing, Competition Cams has produced a simple, comprehensive video (part #190) that will take you step by step through the process.
09-26-2002, 10:09 PM
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Re: The facts about LSA on cams </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by JWRENCH:
<strong>Well now I'm confused, <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> cause Comp cams says a lower LSA moves the power peak lower in the rpm range. This is off their website. Here take a look...
The last thing we will discuss is the difference between intake centerline and lobe separation angle. These two terms are often confused. Even though they have very similar names, they are very different and control different events in the engine. Lobe separation angle is simply what it says. It is the number of degrees separating the peak lift point of the exhaust lobe and the peak point of the intake lobe. This is sometimes referred to as the "lobe center" of the cam, but we prefer to call it the lobe separation angle. This can only be changed when the cam is ground. It makes no difference how you degree the cam in the engine, the lobe separation angle is ground into the cam. The intake centerline, on the other hand, 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. Figure 1 shows a normal 270 degree cam. It has a lobe separation of 110°. We show it installed in the engine 4° advanced, or at 106° intake centerline. The light grey curves show the same camshaft installed an additional four degrees advanced, or at 102 degrees intake centerline. You can see how much earlier overlap is taking place and how the intake valve is open a great deal before the piston starts down. This is usually considered as a way to increase bottom end power, but as you can see there is much of the charge pushed out the exhaust, making a less efficient engine. There is a recommended intake centerline installation point on each cam card, and it is important to install the cam at this point. As far as the mechanics of cam degreeing, Competition Cams has produced a simple, comprehensive video (part #190) that will take you step by step through the process.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Based on what you posted, I think they are trying to say that by advancing the degreeing of the cam they are moving the fixed event of ground in overlap earlier, which increases the bottom end power. I dont see that they are meaning spreading or closing the actual LSA in what you posted to do that.
<strong>Well now I'm confused, <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> cause Comp cams says a lower LSA moves the power peak lower in the rpm range. This is off their website. Here take a look...
The last thing we will discuss is the difference between intake centerline and lobe separation angle. These two terms are often confused. Even though they have very similar names, they are very different and control different events in the engine. Lobe separation angle is simply what it says. It is the number of degrees separating the peak lift point of the exhaust lobe and the peak point of the intake lobe. This is sometimes referred to as the "lobe center" of the cam, but we prefer to call it the lobe separation angle. This can only be changed when the cam is ground. It makes no difference how you degree the cam in the engine, the lobe separation angle is ground into the cam. The intake centerline, on the other hand, 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. Figure 1 shows a normal 270 degree cam. It has a lobe separation of 110°. We show it installed in the engine 4° advanced, or at 106° intake centerline. The light grey curves show the same camshaft installed an additional four degrees advanced, or at 102 degrees intake centerline. You can see how much earlier overlap is taking place and how the intake valve is open a great deal before the piston starts down. This is usually considered as a way to increase bottom end power, but as you can see there is much of the charge pushed out the exhaust, making a less efficient engine. There is a recommended intake centerline installation point on each cam card, and it is important to install the cam at this point. As far as the mechanics of cam degreeing, Competition Cams has produced a simple, comprehensive video (part #190) that will take you step by step through the process.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Based on what you posted, I think they are trying to say that by advancing the degreeing of the cam they are moving the fixed event of ground in overlap earlier, which increases the bottom end power. I dont see that they are meaning spreading or closing the actual LSA in what you posted to do that.
09-26-2002, 10:09 PM
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Re: The facts about LSA on cams Actually that's the lobe centerline, not lsa changing. Sorry that was a useless post, and I'm a dumb *** too boot... <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />
09-26-2002, 10:12 PM
#5
Re: The facts about LSA on cams Lobe centerline & lobe separation angle.Two different things that are very often thought of as the same,hence all the confusion as to what LSA moves the RPM in what direction. Another good thread going on now in this section titled "LSA Questions"
JWRENCH...very good explaination of the difference between the two from Comp Cams
JWRENCH...very good explaination of the difference between the two from Comp Cams
09-26-2002, 11:08 PM
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Re: The facts about LSA on cams I'm not getting this LSA thing. heres someone else saying 112 down low, 114 up hi <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> What's the deal?
What is "lobe separation angle?" I know that the number affects idle
quality, and they all seem to hover around 112-116 or so.
...Lobe separation is the distance (in camshaft degrees) that the intake and exhaust lobe centerlines (for a given cylinder) are spread apart. Lobe separation is a physical characteristic of the camshaft and cannot be changed without regrinding the lobes. This separation determines where peak torque will occur within the engine’s power range. Tight lobe separations (such as 110°) cause the peak torque to build early in basic RPM range of the cam. The torque will be concentrated, build quickly and peak out. Broader lobe separations (such as 114°) allows the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM.
Low=
106 to 110 on a normal SBC.
110 to 112 on a LS1.
High=
112 to 114 on a normal SBC
113 to 116 on a LS1 .................................................. ......
What is "lobe separation angle?" I know that the number affects idle
quality, and they all seem to hover around 112-116 or so.
...Lobe separation is the distance (in camshaft degrees) that the intake and exhaust lobe centerlines (for a given cylinder) are spread apart. Lobe separation is a physical characteristic of the camshaft and cannot be changed without regrinding the lobes. This separation determines where peak torque will occur within the engine’s power range. Tight lobe separations (such as 110°) cause the peak torque to build early in basic RPM range of the cam. The torque will be concentrated, build quickly and peak out. Broader lobe separations (such as 114°) allows the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM.
Low=
106 to 110 on a normal SBC.
110 to 112 on a LS1.
High=
112 to 114 on a normal SBC
113 to 116 on a LS1 .................................................. ......
09-26-2002, 11:20 PM
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Re: The facts about LSA on cams </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by JWRENCH:
<strong>I'm not getting this LSA thing. heres someone else saying 112 down low, 114 up hi <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> What's the deal? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Im not sure what that person is trying to say. Its confusing so I would ignore it.
If nothing else, just remember this to be true:
If the LSA is larger(wider), the power range is widened and shifted down.
If the LSA is smaller(narrower), the power range is narrowed and shifted up.
<strong>I'm not getting this LSA thing. heres someone else saying 112 down low, 114 up hi <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> What's the deal? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Im not sure what that person is trying to say. Its confusing so I would ignore it.
If nothing else, just remember this to be true:
If the LSA is larger(wider), the power range is widened and shifted down.
If the LSA is smaller(narrower), the power range is narrowed and shifted up.
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09-26-2002, 11:39 PM
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Re: The facts about LSA on cams Quoted by Bill "Grumpy" Jenkins:
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Changing the centers will alter the engines characteristics to some extent. If the centers are spread, the engine range is wider, and shifted toward the low end of the scale. Cams used in stock engines with high rev potential are often ground with centers as wide as 114 degrees. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Stated by JWRENCH:
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Broader lobe separations (such as 114°) allows the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">These two contradict each other.
The first statement is correct: The wider LSA (such as 114LSA) BROADENS and shifts power LOWER in the rpm band when compared to a 112LSA.
In my opinion the wider, lower power band of the 114LSA is better for larger duration cams intended for street use. This is especially needed when an automatic transmission which has a larger RPM drop between gears is used.
<small>[ September 27, 2002, 12:48 AM: Message edited by: gto69judge ]</small>
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Changing the centers will alter the engines characteristics to some extent. If the centers are spread, the engine range is wider, and shifted toward the low end of the scale. Cams used in stock engines with high rev potential are often ground with centers as wide as 114 degrees. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Stated by JWRENCH:
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Broader lobe separations (such as 114°) allows the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">These two contradict each other.
The first statement is correct: The wider LSA (such as 114LSA) BROADENS and shifts power LOWER in the rpm band when compared to a 112LSA.
In my opinion the wider, lower power band of the 114LSA is better for larger duration cams intended for street use. This is especially needed when an automatic transmission which has a larger RPM drop between gears is used.
<small>[ September 27, 2002, 12:48 AM: Message edited by: gto69judge ]</small>
09-27-2002, 07:55 AM
#9
Re: The facts about LSA on cams WOW...this gets more confusing each time a thread is started on this subject. First of all,the difference between the two LSA's is minimal,except that the lower LSA will idle noticably rougher. The difference after that is minimal.However I will try to explain this as I remember it;
The lower LSA will start it's powerband later & fall off sooner than a wider LSA.It will have it's AVERAGE powerband at a higher RPM,however the RPM at which a lower LSA makes PEAK power is SLIGHTLY lower than a higher LSA
The lower LSA will start it's powerband later & fall off sooner than a wider LSA.It will have it's AVERAGE powerband at a higher RPM,however the RPM at which a lower LSA makes PEAK power is SLIGHTLY lower than a higher LSA
09-27-2002, 08:22 AM
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Re: The facts about LSA on cams </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by AFTICA:
<strong>,however the RPM at which a lower LSA makes PEAK power is SLIGHTLY lower than a higher LSA</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I disagree. Yes you are right, in that the power band narrows with tighter lobe seperation, but where performance is wanted in high rpm where you can generate more power (RPM = HP), a lesser LSA is used. For example, Jenkins used as tight as a 109 LSA, for his SB motors that spun 8+ grand. Someting a wider LSA would not work for.
<strong>,however the RPM at which a lower LSA makes PEAK power is SLIGHTLY lower than a higher LSA</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I disagree. Yes you are right, in that the power band narrows with tighter lobe seperation, but where performance is wanted in high rpm where you can generate more power (RPM = HP), a lesser LSA is used. For example, Jenkins used as tight as a 109 LSA, for his SB motors that spun 8+ grand. Someting a wider LSA would not work for.
09-27-2002, 08:54 AM
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Re: The facts about LSA on cams Sorry Kewl, but sometimes even the experts need to be questioned.
The tighter LSA will do following:
open exhaust later in the power to exhaust phase.
open intake earlier and close it earlier in the induction to compression phase.
This will - provide less cyllinder fill off idle, but reach peak dynamic compression earlier in the powerband.
TQ curve will be shorter but more pronounced
than a Wide LSA.
Powerband is usually shorter but more pronounced with tight lsa.
I
The tighter LSA will do following:
open exhaust later in the power to exhaust phase.
open intake earlier and close it earlier in the induction to compression phase.
This will - provide less cyllinder fill off idle, but reach peak dynamic compression earlier in the powerband.
TQ curve will be shorter but more pronounced
than a Wide LSA.
Powerband is usually shorter but more pronounced with tight lsa.
I
09-27-2002, 09:06 AM
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Re: The facts about LSA on cams I like my 116LSA cam.. most of the power is low and midrange just where I want it for the street.
I~ll dyno it soon to see if that`s just my imagination cause I`ve always believed :
If the LSA is larger(wider), the power range is widened and shifted down.
If the LSA is smaller(narrower), the power range is narrowed and shifted up.
I~ll dyno it soon to see if that`s just my imagination cause I`ve always believed :
If the LSA is larger(wider), the power range is widened and shifted down.
If the LSA is smaller(narrower), the power range is narrowed and shifted up.
09-27-2002, 09:38 AM
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Re: The facts about LSA on cams </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by HP-GURU:
<strong>Sorry Kewl, but sometimes even the experts need to be questioned.
The tighter LSA will do following:
open exhaust later in the power to exhaust phase.
open intake earlier and close it earlier in the induction to compression phase.
This will - provide less cyllinder fill off idle, but reach peak dynamic compression earlier in the powerband.
TQ curve will be shorter but more pronounced
than a Wide LSA.
Powerband is usually shorter but more pronounced with tight lsa.
I</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Ok, based on your assertion. I gather you beleive the following to be true:
Tighter LSA = narrower powerband
(that is in line with jenkins)
Tighter LSA provides less cyllinder fill off idle, but reaches peak dynamic compression earlier in the powerband.
(Jenkins disagrees with you here. In that a tighter LSA moves the power range up, to take advantage of flow and rpm in the higher rpm range)
We see that extreme engines use lesser LSA to make more power in the upper RPM range. Even tho its a narrower range. This is evident for example in the 109 LSA used in Jenkins extreme RPM motors.
With that said, does that mean very tight LSA's are good for the street? No, because motors that make extreme power at high RPM with tight LSA, have a narrow powerband up high, which is really suited to optimal low gearing to keep the rpms up. As in an all out drag motor.
Based on Jenkins, and my perspective also, this is how I see it.
<img src="http://www.vetteguru.com/misc/lsa.gif" alt=" - " />
I'd hate to beleive that Jenkins could have had it all wrong when he is considered a mozart of the SB Chevy in Drag Racing and Nascar. He was a pioneer of what we take for granted today.
<small>[ September 27, 2002, 10:59 AM: Message edited by: kewlbrz ]</small>
<strong>Sorry Kewl, but sometimes even the experts need to be questioned.
The tighter LSA will do following:
open exhaust later in the power to exhaust phase.
open intake earlier and close it earlier in the induction to compression phase.
This will - provide less cyllinder fill off idle, but reach peak dynamic compression earlier in the powerband.
TQ curve will be shorter but more pronounced
than a Wide LSA.
Powerband is usually shorter but more pronounced with tight lsa.
I</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Ok, based on your assertion. I gather you beleive the following to be true:
Tighter LSA = narrower powerband
(that is in line with jenkins)
Tighter LSA provides less cyllinder fill off idle, but reaches peak dynamic compression earlier in the powerband.
(Jenkins disagrees with you here. In that a tighter LSA moves the power range up, to take advantage of flow and rpm in the higher rpm range)
We see that extreme engines use lesser LSA to make more power in the upper RPM range. Even tho its a narrower range. This is evident for example in the 109 LSA used in Jenkins extreme RPM motors.
With that said, does that mean very tight LSA's are good for the street? No, because motors that make extreme power at high RPM with tight LSA, have a narrow powerband up high, which is really suited to optimal low gearing to keep the rpms up. As in an all out drag motor.
Based on Jenkins, and my perspective also, this is how I see it.
<img src="http://www.vetteguru.com/misc/lsa.gif" alt=" - " />
I'd hate to beleive that Jenkins could have had it all wrong when he is considered a mozart of the SB Chevy in Drag Racing and Nascar. He was a pioneer of what we take for granted today.
<small>[ September 27, 2002, 10:59 AM: Message edited by: kewlbrz ]</small>
09-27-2002, 11:05 AM
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Re: The facts about LSA on cams Then why does a B1 (114 LSA) peak higher than a T1 (112 LSA)? All of the popular hot rodding mags have done dyno shootouts with varying LSAs and the wider LSAs ALWAYS pushed the powerband up higher.
09-27-2002, 11:10 AM
#15
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Re: The facts about LSA on cams </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Fenris Ulf:
<strong>Then why does a B1 (114 LSA) peak higher than a T1 (112 LSA)? All of the popular hot rodding mags have done dyno shootouts with varying LSAs and the wider LSAs ALWAYS pushed the powerband up higher.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">good question.
i would also ask why do engines built for high rpm extreme conditions have tight LSA's ?
<strong>Then why does a B1 (114 LSA) peak higher than a T1 (112 LSA)? All of the popular hot rodding mags have done dyno shootouts with varying LSAs and the wider LSAs ALWAYS pushed the powerband up higher.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">good question.
i would also ask why do engines built for high rpm extreme conditions have tight LSA's ?
09-27-2002, 11:18 AM
#16
Re: The facts about LSA on cams The reason why the B1 (114 LSA) peaks higher than the T1 (112 LSA) is because the B1 closes the intake valve 2 degrees later than the T1. The intake closing point is the single most important aspect to where a motor makes its peak power. Close the intake valve later and it moves the peak up in the rpm scale. If you retarded the intake centerline of the T1 cam 2 degrees, the intake closing point would be the same as the B1 and the power peaks would be nearly identical.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
LS1,LS2,LS3,LS7,LT1 Custom Camshaft Specialist For custom camshaft help press here.
Custom LSX tuning in person or via email press here.
09-27-2002, 11:40 AM
#17
Re: The facts about LSA on cams I still stand by my opinion that the higher LSA will move the PEAK HP rpm UP slightly. HP-GURU & Patrick G gave the explanation as to why.
KEWL.. As for your question as to why engines built for high RPM conditions use tighter LSA's is that they have to with the long duration of all out race cams.
KEWL.. As for your question as to why engines built for high RPM conditions use tighter LSA's is that they have to with the long duration of all out race cams.
09-27-2002, 01:01 PM
#18
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Re: The facts about LSA on cams HP-GURU - Dont you hate it when you spend alot of thought on a post and someone is 2 minutes quicker to post it.
Personally, I want as much torque as I can get and have it lower in the powerband yet still make decent power to 6200 rpms. Does that mean a conservative duration, more lift and tighter LSA? hehehe
Personally, I want as much torque as I can get and have it lower in the powerband yet still make decent power to 6200 rpms. Does that mean a conservative duration, more lift and tighter LSA? hehehe
09-27-2002, 01:04 PM
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Re: The facts about LSA on cams Could be interesting. Now a stock headed car will benefit more from the air exchange because it is intake limited.
One way around that is a tuned exhaust and getting that air exchange started earlier.
LGM Long tubes with good 3" exhaust,
tight LSA high lift short duration cam should prove to be interesting.
I was thinking 108LSA's before, but heck
106 should'nt be that bad with 218. You have
alot of guys with the 230/224 on 111. This should have similar overlap.
What is the cross section on the LS6 intake?
WHat is the runner length?
Need to find out what RPM band its tuned for, and have all parts working in synergy.
One way around that is a tuned exhaust and getting that air exchange started earlier.
LGM Long tubes with good 3" exhaust,
tight LSA high lift short duration cam should prove to be interesting.
I was thinking 108LSA's before, but heck
106 should'nt be that bad with 218. You have
alot of guys with the 230/224 on 111. This should have similar overlap.
What is the cross section on the LS6 intake?
WHat is the runner length?
Need to find out what RPM band its tuned for, and have all parts working in synergy.
09-27-2002, 01:07 PM
#20
Re: The facts about LSA on cams Big Tex... "does more valve duration lower the effective LSA of a cam?" No,nothing changes LSA but it depends on what you mean by "effective".
"The nature of long duration makes more overlap." Generally yes,but you could widen the LSA to get the same or less overlap.
Your example is generally correct.I would like to know how you calculated the LSA for the 218 cam though.I don't think the calculation is that linear and there are more variables involved.
"The nature of long duration makes more overlap." Generally yes,but you could widen the LSA to get the same or less overlap.
Your example is generally correct.I would like to know how you calculated the LSA for the 218 cam though.I don't think the calculation is that linear and there are more variables involved.