Effects of Change in LSA discussion
03-21-2006, 08:01 AM
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Effects of Change in LSA discussion
I can't stand it any longer. I have seen time and time again on this board where people are saying that a tighter lobe seperation angle on a cam (lower numerical) will bring the power band in sooner. From my 15 years building high performance engines and research this theory is absolutely not true. The wider the lsa (higher numerical) the wider the power band thus the sooner the cam will come in. Also the wider the lsa the smoother the idle due to less overlap which allows more efficient breathing of the cyl at low rpm. The tighter the LSA the more efficient the cyl breaths at high rpm and the more peak hp you will make but have a tighter power band. What I'd like to know is where you guys are getting your information from about how a tighter lsa will bring the power band in sooner? People please inform. 
Here is one link I got on a yahoo search that backs up my knowledge. If there is one person in this world that would know it would be Gumpy Jenkins. Link
Here is one link I got on a yahoo search that backs up my knowledge. If there is one person in this world that would know it would be Gumpy Jenkins. Link
03-21-2006, 08:33 AM
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An LS type motor will work with wider LSA than a regular small block,because the heads flow so much better.What Grumpy says is true,but the playing field changed with the LS1.
03-21-2006, 09:12 AM
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Originally Posted by whitt1
An LS type motor will work with wider LSA than a regular small block,because the heads flow so much better.What Grumpy says is true,but the playing field changed with the LS1.
03-21-2006, 09:22 AM
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Originally Posted by mjhoward
I can't stand it any longer. I have seen time and time again on this board where people are saying that a tighter lobe seperation angle on a cam (lower numerical) will bring the power band in sooner. From my 15 years building high performance engines and research this theory is absolutely not true. The wider the lsa (higher numerical) the wider the power band thus the sooner the cam will come in. Also the wider the lsa the smoother the idle due to less overlap which allows more efficient breathing of the cyl at low rpm. The tighter the LSA the more efficient the cyl breaths at high rpm and the more peak hp you will make but have a tighter power band. What I'd like to know is where you guys are getting your information from about how a tighter lsa will bring the power band in sooner? People please inform.
Here is one link I got on a yahoo search that backs up my knowledge. If there is one person in this world that would know it would be Gumpy Jenkins. Link
Here is one link I got on a yahoo search that backs up my knowledge. If there is one person in this world that would know it would be Gumpy Jenkins. Link
03-21-2006, 10:05 AM
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Originally Posted by FarmerBeau
Damn Mark!! Tell em' who their daddy is! haha
That boy ain't right.
"They sent me home from the nervous hospital, said I was well. Umm hmmm."
03-21-2006, 11:39 AM
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Here's an article I like: http://www.chevyhiperformance.com/techarticles/95298/
Some highlights for this conversation. The way I read it this supports your view, Mark.:
"An unfortunate result of excessive overlap is reduced torque and soft throttle response at low engine speeds (e.g., below 3,000 rpm). "
"The difficulty with overlap is that the results change with different engine speeds. Since race engines tend to operate in relatively narrow rpm bands (e.g., 5,000 to 7,500 rpm), it’s easier to design a cam to work in this rpm band. A street engine is a greater challenge because it must operate through a rpm band of 5,000 rpm or more (1,000 to 6,000 rpm). The key to making overlap work is maximizing the power in the rpm band where you want it. Long overlap periods work best for high-rpm power. For the street, a long overlap period combined with long-duration profiles combine to kill low-speed torque. This makes for a soggy street engine at low engine speeds. Reducing overlap on a long-duration cam will often increase midrange torque at the expense of peak power, but if the average torque improves, that’s probably a change worth making
The most important point in the four-stroke cycle is the intake closing point. While this is not part of overlap, the timing of intake opening and closing determines total duration. The intake closing point is a big determiner in where the engine makes power. A later intake closing point improves top-end power. Combine that with more overlap and you have a cam designed to make power at high rpm. However, it’s possible to decrease overlap by using a shorter-duration intake lobe and retard the intake centerline (which spreads the lobe separation angle) to improve midrange power. "
Andrew
Some highlights for this conversation. The way I read it this supports your view, Mark.:
"An unfortunate result of excessive overlap is reduced torque and soft throttle response at low engine speeds (e.g., below 3,000 rpm). "
"The difficulty with overlap is that the results change with different engine speeds. Since race engines tend to operate in relatively narrow rpm bands (e.g., 5,000 to 7,500 rpm), it’s easier to design a cam to work in this rpm band. A street engine is a greater challenge because it must operate through a rpm band of 5,000 rpm or more (1,000 to 6,000 rpm). The key to making overlap work is maximizing the power in the rpm band where you want it. Long overlap periods work best for high-rpm power. For the street, a long overlap period combined with long-duration profiles combine to kill low-speed torque. This makes for a soggy street engine at low engine speeds. Reducing overlap on a long-duration cam will often increase midrange torque at the expense of peak power, but if the average torque improves, that’s probably a change worth making
The most important point in the four-stroke cycle is the intake closing point. While this is not part of overlap, the timing of intake opening and closing determines total duration. The intake closing point is a big determiner in where the engine makes power. A later intake closing point improves top-end power. Combine that with more overlap and you have a cam designed to make power at high rpm. However, it’s possible to decrease overlap by using a shorter-duration intake lobe and retard the intake centerline (which spreads the lobe separation angle) to improve midrange power. "
Andrew
Nice. wait...... 
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03-21-2006, 01:51 PM
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Originally Posted by agreif
Here's an article I like: http://www.chevyhiperformance.com/techarticles/95298/
Some highlights for this conversation. The way I read it this supports your view, Mark.:
"An unfortunate result of excessive overlap is reduced torque and soft throttle response at low engine speeds (e.g., below 3,000 rpm). "
"The difficulty with overlap is that the results change with different engine speeds. Since race engines tend to operate in relatively narrow rpm bands (e.g., 5,000 to 7,500 rpm), it’s easier to design a cam to work in this rpm band. A street engine is a greater challenge because it must operate through a rpm band of 5,000 rpm or more (1,000 to 6,000 rpm). The key to making overlap work is maximizing the power in the rpm band where you want it. Long overlap periods work best for high-rpm power. For the street, a long overlap period combined with long-duration profiles combine to kill low-speed torque. This makes for a soggy street engine at low engine speeds. Reducing overlap on a long-duration cam will often increase midrange torque at the expense of peak power, but if the average torque improves, that’s probably a change worth making
The most important point in the four-stroke cycle is the intake closing point. While this is not part of overlap, the timing of intake opening and closing determines total duration. The intake closing point is a big determiner in where the engine makes power. A later intake closing point improves top-end power. Combine that with more overlap and you have a cam designed to make power at high rpm. However, it’s possible to decrease overlap by using a shorter-duration intake lobe and retard the intake centerline (which spreads the lobe separation angle) to improve midrange power. "
Andrew
Some highlights for this conversation. The way I read it this supports your view, Mark.:
"An unfortunate result of excessive overlap is reduced torque and soft throttle response at low engine speeds (e.g., below 3,000 rpm). "
"The difficulty with overlap is that the results change with different engine speeds. Since race engines tend to operate in relatively narrow rpm bands (e.g., 5,000 to 7,500 rpm), it’s easier to design a cam to work in this rpm band. A street engine is a greater challenge because it must operate through a rpm band of 5,000 rpm or more (1,000 to 6,000 rpm). The key to making overlap work is maximizing the power in the rpm band where you want it. Long overlap periods work best for high-rpm power. For the street, a long overlap period combined with long-duration profiles combine to kill low-speed torque. This makes for a soggy street engine at low engine speeds. Reducing overlap on a long-duration cam will often increase midrange torque at the expense of peak power, but if the average torque improves, that’s probably a change worth making
The most important point in the four-stroke cycle is the intake closing point. While this is not part of overlap, the timing of intake opening and closing determines total duration. The intake closing point is a big determiner in where the engine makes power. A later intake closing point improves top-end power. Combine that with more overlap and you have a cam designed to make power at high rpm. However, it’s possible to decrease overlap by using a shorter-duration intake lobe and retard the intake centerline (which spreads the lobe separation angle) to improve midrange power. "
Andrew
03-21-2006, 01:54 PM
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It has been my understanding that the smaller the LSA, the shorter the power band. Also, I have always looked at it backwards in that peak will always be peak. So that if peak is 6000 rpm, a LSA of 112 may go back to say 3500 rpms and a 114 may go back to 3000 rpms. Of course there are other factors that play part in the powerband.
This also why cam and gear and stall (if you have one) selection are important.
This also why cam and gear and stall (if you have one) selection are important.
03-21-2006, 02:13 PM
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Originally Posted by Silver-Dollar
This also why cam and gear and stall (if you have one) selection are important.
Also, where CHP says, "Since race engines tend to operate in relatively narrow rpm bands (e.g., 5,000 to 7,500 rpm), it’s easier to design a cam to work in this rpm band". I have seen cams in catalogs for roundtrack racing with as short of a LSA as 98*. This is due to help it breath in the high and narrow rpm band they run in.