427 Cam Experts, need perfect cam for max effort street/strip 427!
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Originally Posted by 71CamaroLS1
If I might throw something out here that might dampen the fire - or might blow it up
- engines really don't give a damn about LSA, *per se*. LSA is a convenience for the cam grinder, but from an engine performance standpoint all LSA does is change the relationships between the IVO/IVC and EVO/EVC events. (Guide to acronyms: I = intake, E = exhaust, V = valve, O = open, C = close, e.g. IVC = intake valve close). LSA is the angular separation between the intake lobe and the exhaust lobe. So if you narrow LSA, what will happen is that IVO and IVC will happen earlier relative to EVO and EVC. If you reduce the intake centerline (ICL) at the same time, the IVO/IVC and EVO/EVC events will happen earlier relative to *crankshaft position*. It is the relationship between IVO/IVC events and EVO/EVC events, and the timing of those events relative to crankshaft position, that really matter to the engine. I know Patrick G and GrannySS know these things, but it's worth reviewing it for all those who might be following this thread and just wanting to know "what LSA should I use!" without knowing what LSA really means.
Now, relative to the discussion about stroke and displacement versus LSA - this gets very complicated indeed. First off, recognize that the velocity of the piston down the bore reaches its maximum before 90 degrees past TDC (top dead center). Just draw some pictures of the crank/rod/piston configuration at various angles if you don't believe this. Or look at this link: http://www.epi-eng.com/ET-PistnVelAccel.htm for an example. Now, notice that real world cams don't reach maximum intake lift until *after* 90 degrees past TDC - for instance, if your ICL is 110, your intake valve reaches maximum lift at 110 degrees after TDC. So, at the point where the piston is "sucking" the hardest on the intake stroke, the intake valve is not yet all the way open. This creates performance problems, particularly on a 2-valve engine, because 2 valve engines are short on what is called "curtain area", which means, among other things, that they need the valves open a long way to flow well. This is what Patrick means when he talks about "under-valved".
Now, when you increase displacement, for a given head, the engine does indeed become even more "under valved". This would suggest that you open the intake valve earlier, which means in cam grinder terms some combination of more intake duration and/or earlier ICL. There is another factor associated with greater stroke - if you keep rod length the same, but increase stroke, max piston velocity occurs earlier - even more reason to open the intake valve earlier. But to counter those two factors: the increased displacement will create increased air velocity for a given head/intake. This increased air velocity means increased air momentum in the intake tract, which means that the cylinder will continue to fill for longer after the piston begins to move up the bore in the compression stroke. To take advantage of this effect, we want to close the intake valve later.
Completely ignoring the exhaust side of things for a moment, increasing stroke and displacement means that we want earlier IVO and later IVC (meaning, for sure, more duration). *How much earlier and how much later* will determine how the LSA changes when we call the cam grinder - if the "opening earlier" effect is greater than the "closing later" effect, we will want less LSA, and if the reverse is true, we will want more LSA. There are some "general rules" derived from real world experience - meaning, often, "experience with 1st gen small block Chevys" - that suggest increasing displacement will call for IVO/IVC tradeoffs that lead to smaller LSA specs. But there are a ton of variables ignored in such a "general rule", and ultimately there is no substitute for real world experience, ideally informed by analysis from advanced engine simulation programs like Dynomation.
The exhaust side of things changes with more displacement too, and further affects EVO and EVC, and thus LSA. No time to comment on that now, will post more later.
Edit:
OK, now for the exhaust side. Exhaust gasses have very large volume, and are under very high pressure. When considering exhaust valve open (EVO), we are balancing two things. First, we want to open the exhaust value early, so as to let the high pressure exhaust gasses escape before the piston starts back up the bore (bottom dead center, or BDC). High pressure after BDC works against us, and robs power. So we want most of the exhaust pressure dissipated before BDC. This exhaust pressure dissipation is known as exhaust "blowdown". On the other hand, we don't want to dissipate exhaust pressure too soon before BDC, because that pressure is exactly what the engine uses to create power (that pressure, in engineering terms, is known as Brake Mean Effective Pressure, or BMEP). The optimum point for opening the exhaust value depends on the "blowdown" event time, and therefore is dependent on desired RPM range.
Incidentally, exhaust "blowdown" is mostly complete before the exhaust valve opens very far at all. Thus, very low level exhaust flow - below .100 inch - is very important in cylinder head design.
Now, the piston starts up the bore for the "exhaust stroke". There is still quite a bit of exhaust gas volume in the cylinder at this point, and the goal is to minimize the pressure on top of the piston as the piston exhausts the rest of this gas, since any pressure on the piston at this point just steals power from us. So we want max exhaust flow when the piston is moving most quickly - when the piston is past 90 degrees after bottom dead center (ABDC). Once again, if the rod length length is short compared to the stroke length, the point where the piston moves most quickly will be closer to top dead center (TDC) - which says that we want max exhaust lift closer to TDC, which says that we want less LSA (ignoring intake considerations, for the moment).
Finally, we reach the point where the piston nears TDC on the exhaust stroke, and the intake valve opens, beginning the overlap zone. Overlap is very important to a high performance engine, because overlap uses energy from the exhaust system to help move fuel/air through the intake system - but only if your exhaust (headers) and intake (manifold) are tuned to help each other in your desired RPM range. Increasing displacement means that you might want to increase overlap more than it is already increased by earlier IVO (see above), and therefore close the exhaust later (later EVC). The balance of earlier EVO versus later EVC will determine whether LSA is smaller or larger, assuming constant IVC/IVO. The details of how overlap works to create what David Vizard calls a "5 cycle engine" are beyond a simple forum post - for those with appetite for a moderately technical description, download the users manual for Dynomation, and read the section called "Wave-Dynamics Analysis" beginning page 231: http://www.proracingsim.com/download...sersManual.pdf . Unfortunately, a 44MB download, but well worth it for those seeking a shortcut to graduate-degree level knowledge of high-performance engine behavior.
If all of the above sounds complicated, it is. And it's further complicated by the behavior of your intake and exhaust systems - in fact, ideally, your intake, headers, cylinder head, compression ratio, rod/stroke ratio, and cam should all be designed together for your ideal balance of displacement, desired power, RPM range, idle and part throttle drivability, etc. But headers, intake, heads, CR, rod/stroke are all much harder to change than cam, which is why we have so many "perfect cam" threads!
None of the above is intended to suggest that I know more than the experienced gurus about cam selection for LS series motors that the other gentlemen on this thread - indeed, I know far less. But hopefully this is a guide to asking intelligent questions from your cam designer - "why close the intake later, or open it sooner/later" or "why open exhaust sooner" or "what is the optimum compression for your IVC" or "does the RPM range of your cam match my intake" or "do I need an earlier EVO considering I'm using stock exhaust" or other such pertinent questions. And then let the cam specs - duration, LSA, ICL - be determined by the answers to those questions, rather than allowing those specs to be goals in themselves.
![Happy](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_stretch.gif)
Now, relative to the discussion about stroke and displacement versus LSA - this gets very complicated indeed. First off, recognize that the velocity of the piston down the bore reaches its maximum before 90 degrees past TDC (top dead center). Just draw some pictures of the crank/rod/piston configuration at various angles if you don't believe this. Or look at this link: http://www.epi-eng.com/ET-PistnVelAccel.htm for an example. Now, notice that real world cams don't reach maximum intake lift until *after* 90 degrees past TDC - for instance, if your ICL is 110, your intake valve reaches maximum lift at 110 degrees after TDC. So, at the point where the piston is "sucking" the hardest on the intake stroke, the intake valve is not yet all the way open. This creates performance problems, particularly on a 2-valve engine, because 2 valve engines are short on what is called "curtain area", which means, among other things, that they need the valves open a long way to flow well. This is what Patrick means when he talks about "under-valved".
Now, when you increase displacement, for a given head, the engine does indeed become even more "under valved". This would suggest that you open the intake valve earlier, which means in cam grinder terms some combination of more intake duration and/or earlier ICL. There is another factor associated with greater stroke - if you keep rod length the same, but increase stroke, max piston velocity occurs earlier - even more reason to open the intake valve earlier. But to counter those two factors: the increased displacement will create increased air velocity for a given head/intake. This increased air velocity means increased air momentum in the intake tract, which means that the cylinder will continue to fill for longer after the piston begins to move up the bore in the compression stroke. To take advantage of this effect, we want to close the intake valve later.
Completely ignoring the exhaust side of things for a moment, increasing stroke and displacement means that we want earlier IVO and later IVC (meaning, for sure, more duration). *How much earlier and how much later* will determine how the LSA changes when we call the cam grinder - if the "opening earlier" effect is greater than the "closing later" effect, we will want less LSA, and if the reverse is true, we will want more LSA. There are some "general rules" derived from real world experience - meaning, often, "experience with 1st gen small block Chevys" - that suggest increasing displacement will call for IVO/IVC tradeoffs that lead to smaller LSA specs. But there are a ton of variables ignored in such a "general rule", and ultimately there is no substitute for real world experience, ideally informed by analysis from advanced engine simulation programs like Dynomation.
The exhaust side of things changes with more displacement too, and further affects EVO and EVC, and thus LSA. No time to comment on that now, will post more later.
Edit:
OK, now for the exhaust side. Exhaust gasses have very large volume, and are under very high pressure. When considering exhaust valve open (EVO), we are balancing two things. First, we want to open the exhaust value early, so as to let the high pressure exhaust gasses escape before the piston starts back up the bore (bottom dead center, or BDC). High pressure after BDC works against us, and robs power. So we want most of the exhaust pressure dissipated before BDC. This exhaust pressure dissipation is known as exhaust "blowdown". On the other hand, we don't want to dissipate exhaust pressure too soon before BDC, because that pressure is exactly what the engine uses to create power (that pressure, in engineering terms, is known as Brake Mean Effective Pressure, or BMEP). The optimum point for opening the exhaust value depends on the "blowdown" event time, and therefore is dependent on desired RPM range.
Incidentally, exhaust "blowdown" is mostly complete before the exhaust valve opens very far at all. Thus, very low level exhaust flow - below .100 inch - is very important in cylinder head design.
Now, the piston starts up the bore for the "exhaust stroke". There is still quite a bit of exhaust gas volume in the cylinder at this point, and the goal is to minimize the pressure on top of the piston as the piston exhausts the rest of this gas, since any pressure on the piston at this point just steals power from us. So we want max exhaust flow when the piston is moving most quickly - when the piston is past 90 degrees after bottom dead center (ABDC). Once again, if the rod length length is short compared to the stroke length, the point where the piston moves most quickly will be closer to top dead center (TDC) - which says that we want max exhaust lift closer to TDC, which says that we want less LSA (ignoring intake considerations, for the moment).
Finally, we reach the point where the piston nears TDC on the exhaust stroke, and the intake valve opens, beginning the overlap zone. Overlap is very important to a high performance engine, because overlap uses energy from the exhaust system to help move fuel/air through the intake system - but only if your exhaust (headers) and intake (manifold) are tuned to help each other in your desired RPM range. Increasing displacement means that you might want to increase overlap more than it is already increased by earlier IVO (see above), and therefore close the exhaust later (later EVC). The balance of earlier EVO versus later EVC will determine whether LSA is smaller or larger, assuming constant IVC/IVO. The details of how overlap works to create what David Vizard calls a "5 cycle engine" are beyond a simple forum post - for those with appetite for a moderately technical description, download the users manual for Dynomation, and read the section called "Wave-Dynamics Analysis" beginning page 231: http://www.proracingsim.com/download...sersManual.pdf . Unfortunately, a 44MB download, but well worth it for those seeking a shortcut to graduate-degree level knowledge of high-performance engine behavior.
If all of the above sounds complicated, it is. And it's further complicated by the behavior of your intake and exhaust systems - in fact, ideally, your intake, headers, cylinder head, compression ratio, rod/stroke ratio, and cam should all be designed together for your ideal balance of displacement, desired power, RPM range, idle and part throttle drivability, etc. But headers, intake, heads, CR, rod/stroke are all much harder to change than cam, which is why we have so many "perfect cam" threads!
None of the above is intended to suggest that I know more than the experienced gurus about cam selection for LS series motors that the other gentlemen on this thread - indeed, I know far less. But hopefully this is a guide to asking intelligent questions from your cam designer - "why close the intake later, or open it sooner/later" or "why open exhaust sooner" or "what is the optimum compression for your IVC" or "does the RPM range of your cam match my intake" or "do I need an earlier EVO considering I'm using stock exhaust" or other such pertinent questions. And then let the cam specs - duration, LSA, ICL - be determined by the answers to those questions, rather than allowing those specs to be goals in themselves.
ALL OF THAT and no recommendations for my motor which by the way will be running the latest and greatest TRICK FLOW 235 Heads ported by TEA!
![Driving](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_driving3.gif)
![Chug! Chug! Chug!](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_chug.gif)
![Driving](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_driving3.gif)
COME ON GUYS, shoot me some cam specs that will make huge power throughout the entire rpm band on my new LME Built 430 CID LS7 MOTOR, that will power my 02 C5 Z06 which will see mostly street duty, some limited drag race duty and some ROAD RACING BABY!
![Driving](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_driving3.gif)
![Driving](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_driving3.gif)
#24
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Originally Posted by Chicago Crew UnderBoss
ALL OF THAT and no recommendations for my motor which by the way will be running the latest and greatest TRICK FLOW 235 Heads ported by TEA
The point is, there are a bunch of potential answers to your question, and only a well-informed consumer and a well-informed builder together are *likely* to find a good answer.
You're on here posting for answers to an ill-defined question (what's the best cam), which is ill-defined because you haven't clearly specified your priorities in terms a good (rare) cam designer can translate to (really good/good/fairly good/pretty choppy idle vs. strong mid range torque vs. high RPM power, or expressed otherwise as good ET/good throttle response/good driveavibility/good top speed tradeoffs). I presumed you don't just want to take your engine builder's word for it, which I presume means you want some education on why your builder is recommending what (s)he is recommending. But obviously I'm wrong.
Maybe you just want to average the internet BS numbers all of your posters will submit. There is a certain logic to that, particularly when the posters have a track record like Patrick. Ultimately, though, you're flying blind if you don't care to understand what a cam actually does in a running engine.
#25
Launching!
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And the good news is, as I've already said, cams are fairly easily replaced if you get it wrong the first time. Which, speaking from experience, is easy to do because your experience and priorities change.
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Originally Posted by MPM IV
I don't have a recommendation, but I did PM you a couple of questions.
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Last edited by Chicago Crew UnderBoss; 04-13-2007 at 04:04 AM.
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Originally Posted by 71CamaroLS1
Yes, and no cure for cancer either! What a f***** bozo I am!
The point is, there are a bunch of potential answers to your question, and only a well-informed consumer and a well-informed builder together are *likely* to find a good answer.
You're on here posting for answers to an ill-defined question (what's the best cam), which is ill-defined because you haven't clearly specified your priorities in terms a good (rare) cam designer can translate to (really good/good/fairly good/pretty choppy idle vs. strong mid range torque vs. high RPM power, or expressed otherwise as good ET/good throttle response/good driveavibility/good top speed tradeoffs). I presumed you don't just want to take your engine builder's word for it, which I presume means you want some education on why your builder is recommending what (s)he is recommending. But obviously I'm wrong.
Maybe you just want to average the internet BS numbers all of your posters will submit. There is a certain logic to that, particularly when the posters have a track record like Patrick. Ultimately, though, you're flying blind if you don't care to understand what a cam actually does in a running engine.
The point is, there are a bunch of potential answers to your question, and only a well-informed consumer and a well-informed builder together are *likely* to find a good answer.
You're on here posting for answers to an ill-defined question (what's the best cam), which is ill-defined because you haven't clearly specified your priorities in terms a good (rare) cam designer can translate to (really good/good/fairly good/pretty choppy idle vs. strong mid range torque vs. high RPM power, or expressed otherwise as good ET/good throttle response/good driveavibility/good top speed tradeoffs). I presumed you don't just want to take your engine builder's word for it, which I presume means you want some education on why your builder is recommending what (s)he is recommending. But obviously I'm wrong.
Maybe you just want to average the internet BS numbers all of your posters will submit. There is a certain logic to that, particularly when the posters have a track record like Patrick. Ultimately, though, you're flying blind if you don't care to understand what a cam actually does in a running engine.
![Happy](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_stretch.gif)
#28
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Originally Posted by 71CamaroLS1
If I might throw something out here that might dampen the fire - or might blow it up
- engines really don't give a damn about LSA, *per se*. LSA is a convenience for the cam grinder, but from an engine performance standpoint all LSA does is change the relationships between the IVO/IVC and EVO/EVC events. (Guide to acronyms: I = intake, E = exhaust, V = valve, O = open, C = close, e.g. IVC = intake valve close). LSA is the angular separation between the intake lobe and the exhaust lobe. So if you narrow LSA, what will happen is that IVO and IVC will happen earlier relative to EVO and EVC. If you reduce the intake centerline (ICL) at the same time, the IVO/IVC and EVO/EVC events will happen earlier relative to *crankshaft position*. It is the relationship between IVO/IVC events and EVO/EVC events, and the timing of those events relative to crankshaft position, that really matter to the engine. I know Patrick G and GrannySS know these things, but it's worth reviewing it for all those who might be following this thread and just wanting to know "what LSA should I use!" without knowing what LSA really means.
Now, relative to the discussion about stroke and displacement versus LSA - this gets very complicated indeed. First off, recognize that the velocity of the piston down the bore reaches its maximum before 90 degrees past TDC (top dead center). Just draw some pictures of the crank/rod/piston configuration at various angles if you don't believe this. Or look at this link: http://www.epi-eng.com/ET-PistnVelAccel.htm for an example. Now, notice that real world cams don't reach maximum intake lift until *after* 90 degrees past TDC - for instance, if your ICL is 110, your intake valve reaches maximum lift at 110 degrees after TDC. So, at the point where the piston is "sucking" the hardest on the intake stroke, the intake valve is not yet all the way open. This creates performance problems, particularly on a 2-valve engine, because 2 valve engines are short on what is called "curtain area", which means, among other things, that they need the valves open a long way to flow well. This is what Patrick means when he talks about "under-valved".
Now, when you increase displacement, for a given head, the engine does indeed become even more "under valved". This would suggest that you open the intake valve earlier, which means in cam grinder terms some combination of more intake duration and/or earlier ICL. There is another factor associated with greater stroke - if you keep rod length the same, but increase stroke, max piston velocity occurs earlier - even more reason to open the intake valve earlier. But to counter those two factors: the increased displacement will create increased air velocity for a given head/intake. This increased air velocity means increased air momentum in the intake tract, which means that the cylinder will continue to fill for longer after the piston begins to move up the bore in the compression stroke. To take advantage of this effect, we want to close the intake valve later.
Completely ignoring the exhaust side of things for a moment, increasing stroke and displacement means that we want earlier IVO and later IVC (meaning, for sure, more duration). *How much earlier and how much later* will determine how the LSA changes when we call the cam grinder - if the "opening earlier" effect is greater than the "closing later" effect, we will want less LSA, and if the reverse is true, we will want more LSA. There are some "general rules" derived from real world experience - meaning, often, "experience with 1st gen small block Chevys" - that suggest increasing displacement will call for IVO/IVC tradeoffs that lead to smaller LSA specs. But there are a ton of variables ignored in such a "general rule", and ultimately there is no substitute for real world experience, ideally informed by analysis from advanced engine simulation programs like Dynomation.
The exhaust side of things changes with more displacement too, and further affects EVO and EVC, and thus LSA. No time to comment on that now, will post more later.
Edit:
OK, now for the exhaust side. Exhaust gasses have very large volume, and are under very high pressure. When considering exhaust valve open (EVO), we are balancing two things. First, we want to open the exhaust value early, so as to let the high pressure exhaust gasses escape before the piston starts back up the bore (bottom dead center, or BDC). High pressure after BDC works against us, and robs power. So we want most of the exhaust pressure dissipated before BDC. This exhaust pressure dissipation is known as exhaust "blowdown". On the other hand, we don't want to dissipate exhaust pressure too soon before BDC, because that pressure is exactly what the engine uses to create power (that pressure, in engineering terms, is known as Brake Mean Effective Pressure, or BMEP). The optimum point for opening the exhaust value depends on the "blowdown" event time, and therefore is dependent on desired RPM range.
Incidentally, exhaust "blowdown" is mostly complete before the exhaust valve opens very far at all. Thus, very low level exhaust flow - below .100 inch - is very important in cylinder head design.
Now, the piston starts up the bore for the "exhaust stroke". There is still quite a bit of exhaust gas volume in the cylinder at this point, and the goal is to minimize the pressure on top of the piston as the piston exhausts the rest of this gas, since any pressure on the piston at this point just steals power from us. So we want max exhaust flow when the piston is moving most quickly - when the piston is past 90 degrees after bottom dead center (ABDC). Once again, if the rod length length is short compared to the stroke length, the point where the piston moves most quickly will be closer to top dead center (TDC) - which says that we want max exhaust lift closer to TDC, which says that we want less LSA (ignoring intake considerations, for the moment).
Finally, we reach the point where the piston nears TDC on the exhaust stroke, and the intake valve opens, beginning the overlap zone. Overlap is very important to a high performance engine, because overlap uses energy from the exhaust system to help move fuel/air through the intake system - but only if your exhaust (headers) and intake (manifold) are tuned to help each other in your desired RPM range. Increasing displacement means that you might want to increase overlap more than it is already increased by earlier IVO (see above), and therefore close the exhaust later (later EVC). The balance of earlier EVO versus later EVC will determine whether LSA is smaller or larger, assuming constant IVC/IVO. The details of how overlap works to create what David Vizard calls a "5 cycle engine" are beyond a simple forum post - for those with appetite for a moderately technical description, download the users manual for Dynomation, and read the section called "Wave-Dynamics Analysis" beginning page 231: http://www.proracingsim.com/download...sersManual.pdf . Unfortunately, a 44MB download, but well worth it for those seeking a shortcut to graduate-degree level knowledge of high-performance engine behavior.
If all of the above sounds complicated, it is. And it's further complicated by the behavior of your intake and exhaust systems - in fact, ideally, your intake, headers, cylinder head, compression ratio, rod/stroke ratio, and cam should all be designed together for your ideal balance of displacement, desired power, RPM range, idle and part throttle drivability, etc. But headers, intake, heads, CR, rod/stroke are all much harder to change than cam, which is why we have so many "perfect cam" threads!
None of the above is intended to suggest that I know more than the experienced gurus about cam selection for LS series motors that the other gentlemen on this thread - indeed, I know far less. But hopefully this is a guide to asking intelligent questions from your cam designer - "why close the intake later, or open it sooner/later" or "why open exhaust sooner" or "what is the optimum compression for your IVC" or "does the RPM range of your cam match my intake" or "do I need an earlier EVO considering I'm using stock exhaust" or other such pertinent questions. And then let the cam specs - duration, LSA, ICL - be determined by the answers to those questions, rather than allowing those specs to be goals in themselves.
![Happy](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_stretch.gif)
Now, relative to the discussion about stroke and displacement versus LSA - this gets very complicated indeed. First off, recognize that the velocity of the piston down the bore reaches its maximum before 90 degrees past TDC (top dead center). Just draw some pictures of the crank/rod/piston configuration at various angles if you don't believe this. Or look at this link: http://www.epi-eng.com/ET-PistnVelAccel.htm for an example. Now, notice that real world cams don't reach maximum intake lift until *after* 90 degrees past TDC - for instance, if your ICL is 110, your intake valve reaches maximum lift at 110 degrees after TDC. So, at the point where the piston is "sucking" the hardest on the intake stroke, the intake valve is not yet all the way open. This creates performance problems, particularly on a 2-valve engine, because 2 valve engines are short on what is called "curtain area", which means, among other things, that they need the valves open a long way to flow well. This is what Patrick means when he talks about "under-valved".
Now, when you increase displacement, for a given head, the engine does indeed become even more "under valved". This would suggest that you open the intake valve earlier, which means in cam grinder terms some combination of more intake duration and/or earlier ICL. There is another factor associated with greater stroke - if you keep rod length the same, but increase stroke, max piston velocity occurs earlier - even more reason to open the intake valve earlier. But to counter those two factors: the increased displacement will create increased air velocity for a given head/intake. This increased air velocity means increased air momentum in the intake tract, which means that the cylinder will continue to fill for longer after the piston begins to move up the bore in the compression stroke. To take advantage of this effect, we want to close the intake valve later.
Completely ignoring the exhaust side of things for a moment, increasing stroke and displacement means that we want earlier IVO and later IVC (meaning, for sure, more duration). *How much earlier and how much later* will determine how the LSA changes when we call the cam grinder - if the "opening earlier" effect is greater than the "closing later" effect, we will want less LSA, and if the reverse is true, we will want more LSA. There are some "general rules" derived from real world experience - meaning, often, "experience with 1st gen small block Chevys" - that suggest increasing displacement will call for IVO/IVC tradeoffs that lead to smaller LSA specs. But there are a ton of variables ignored in such a "general rule", and ultimately there is no substitute for real world experience, ideally informed by analysis from advanced engine simulation programs like Dynomation.
The exhaust side of things changes with more displacement too, and further affects EVO and EVC, and thus LSA. No time to comment on that now, will post more later.
Edit:
OK, now for the exhaust side. Exhaust gasses have very large volume, and are under very high pressure. When considering exhaust valve open (EVO), we are balancing two things. First, we want to open the exhaust value early, so as to let the high pressure exhaust gasses escape before the piston starts back up the bore (bottom dead center, or BDC). High pressure after BDC works against us, and robs power. So we want most of the exhaust pressure dissipated before BDC. This exhaust pressure dissipation is known as exhaust "blowdown". On the other hand, we don't want to dissipate exhaust pressure too soon before BDC, because that pressure is exactly what the engine uses to create power (that pressure, in engineering terms, is known as Brake Mean Effective Pressure, or BMEP). The optimum point for opening the exhaust value depends on the "blowdown" event time, and therefore is dependent on desired RPM range.
Incidentally, exhaust "blowdown" is mostly complete before the exhaust valve opens very far at all. Thus, very low level exhaust flow - below .100 inch - is very important in cylinder head design.
Now, the piston starts up the bore for the "exhaust stroke". There is still quite a bit of exhaust gas volume in the cylinder at this point, and the goal is to minimize the pressure on top of the piston as the piston exhausts the rest of this gas, since any pressure on the piston at this point just steals power from us. So we want max exhaust flow when the piston is moving most quickly - when the piston is past 90 degrees after bottom dead center (ABDC). Once again, if the rod length length is short compared to the stroke length, the point where the piston moves most quickly will be closer to top dead center (TDC) - which says that we want max exhaust lift closer to TDC, which says that we want less LSA (ignoring intake considerations, for the moment).
Finally, we reach the point where the piston nears TDC on the exhaust stroke, and the intake valve opens, beginning the overlap zone. Overlap is very important to a high performance engine, because overlap uses energy from the exhaust system to help move fuel/air through the intake system - but only if your exhaust (headers) and intake (manifold) are tuned to help each other in your desired RPM range. Increasing displacement means that you might want to increase overlap more than it is already increased by earlier IVO (see above), and therefore close the exhaust later (later EVC). The balance of earlier EVO versus later EVC will determine whether LSA is smaller or larger, assuming constant IVC/IVO. The details of how overlap works to create what David Vizard calls a "5 cycle engine" are beyond a simple forum post - for those with appetite for a moderately technical description, download the users manual for Dynomation, and read the section called "Wave-Dynamics Analysis" beginning page 231: http://www.proracingsim.com/download...sersManual.pdf . Unfortunately, a 44MB download, but well worth it for those seeking a shortcut to graduate-degree level knowledge of high-performance engine behavior.
If all of the above sounds complicated, it is. And it's further complicated by the behavior of your intake and exhaust systems - in fact, ideally, your intake, headers, cylinder head, compression ratio, rod/stroke ratio, and cam should all be designed together for your ideal balance of displacement, desired power, RPM range, idle and part throttle drivability, etc. But headers, intake, heads, CR, rod/stroke are all much harder to change than cam, which is why we have so many "perfect cam" threads!
None of the above is intended to suggest that I know more than the experienced gurus about cam selection for LS series motors that the other gentlemen on this thread - indeed, I know far less. But hopefully this is a guide to asking intelligent questions from your cam designer - "why close the intake later, or open it sooner/later" or "why open exhaust sooner" or "what is the optimum compression for your IVC" or "does the RPM range of your cam match my intake" or "do I need an earlier EVO considering I'm using stock exhaust" or other such pertinent questions. And then let the cam specs - duration, LSA, ICL - be determined by the answers to those questions, rather than allowing those specs to be goals in themselves.
You're on here posting for answers to an ill-defined question (what's the best cam), which is ill-defined because you haven't clearly specified your priorities in terms a good (rare) cam designer can translate to (really good/good/fairly good/pretty choppy idle vs. strong mid range torque vs. high RPM power, or expressed otherwise as good ET/good throttle response/good driveavibility/good top speed tradeoffs). I presumed you don't just want to take your engine builder's word for it, which I presume means you want some education on why your builder is recommending what (s)he is recommending. But obviously I'm wrong.
Maybe you just want to average the internet BS numbers all of your posters will submit. There is a certain logic to that, particularly when the posters have a track record like Patrick. Ultimately, though, you're flying blind if you don't care to understand what a cam actually does in a running engine.
Yesterday 10:47 PM
Maybe you just want to average the internet BS numbers all of your posters will submit. There is a certain logic to that, particularly when the posters have a track record like Patrick. Ultimately, though, you're flying blind if you don't care to understand what a cam actually does in a running engine.
Yesterday 10:47 PM
I am not being sarcastic, You told it like it was, we need more of that around here....
The point is, there are a bunch of potential answers to your question, and only a well-informed consumer and a well-informed builder together are *likely* to find a good answer
My favorite part, more people should listen to this.
#29
TECH Addict
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![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Originally Posted by Chicago Crew UnderBoss
OH, take a chance brother! ![Happy](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_stretch.gif)
![Happy](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_stretch.gif)
![The Judge](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_judge.gif)
#30
Launching!
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I apologize for the tone and language of my earlier rant, although I stand by the substance.
Maybe another way to put it is, there are three kinds of opinions you can find on one of these forums:
1. Opinions based on reading other people's posts.
2. Opinions based on real world experience.
3. Opinions based on real world experience, with enough understanding of engine science to extrapolate that experience to new situations.
Being educated enough to understand what kind of opinion you're getting can save you lots of money
Maybe another way to put it is, there are three kinds of opinions you can find on one of these forums:
1. Opinions based on reading other people's posts.
2. Opinions based on real world experience.
3. Opinions based on real world experience, with enough understanding of engine science to extrapolate that experience to new situations.
Being educated enough to understand what kind of opinion you're getting can save you lots of money
![Happy](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_stretch.gif)
#31
Launching!
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Here's an example of how to "think like an engine" (thinking in terms of valve events) instead of thinking like a cam grinder (thinking durations and LSA).
Let's use Patrick's example of the perfect cam for a 346 plastic intake motor: 236/240, 110 LSA, +1 (you don't list the advance, so I'm throwing out a number). Patrick has lots of real world experience to back this up.
Now, along comes a new L92 head for 3.9 bore motors. Compared to our known combos with cathedral port heads, this new head has substantially larger intake port, with significantly higher intake flow, but the exhaust side is no better. How should we think about changing our perfect cam to match this head?
Well, thinking in terms of duration and LSA, we see that the exhaust is weaker relative to the intake, and we don't want to change our overlap much, so we spec out something like this: 232/244/110+1. That might work OK, but there is probably a better starting point.
Thinking like an engine, we realize a few things. First, the intake port has a larger cross section, which means that the intake flow velocity will be lower, which means that we probably want to close the intake valve a little sooner to avoid losing power to reversion. Decreasing intake duration will close the valve sooner, but it will also open the valve later, and since the usual problem on a 2 valve motor is not getting the intake open soon enough, maybe we should just advance the ICL. Now, our high flowing intake is filling the cylinder better at high RPM, which means that we'll have more exhaust gas volume, which means that we'll have more exhaust pumping losses, which means that we should think about opening the exhaust valve a bit sooner for earlier exhaust blowdown. So we increase exhaust duration ... but wait, we just advanced the cam for our intake side, so our exhaust valve is already opening sooner! So maybe we don't need more exhaust duration - in fact, maybe all we need to do is advance our existing cam a few degrees.
So we come up with a first try that looks like: 236/240/110 +5. This would be an unlikely first try if we think in terms of durations and LSAs, because it "looks odd" and doesn't match our preconceptions about "large split" being needed for low E/I ratios. But it is a very logical thing to try if you think in terms of valve events, and I'd say there is a better chance it would work than our larger split spec.
Let's use Patrick's example of the perfect cam for a 346 plastic intake motor: 236/240, 110 LSA, +1 (you don't list the advance, so I'm throwing out a number). Patrick has lots of real world experience to back this up.
Now, along comes a new L92 head for 3.9 bore motors. Compared to our known combos with cathedral port heads, this new head has substantially larger intake port, with significantly higher intake flow, but the exhaust side is no better. How should we think about changing our perfect cam to match this head?
Well, thinking in terms of duration and LSA, we see that the exhaust is weaker relative to the intake, and we don't want to change our overlap much, so we spec out something like this: 232/244/110+1. That might work OK, but there is probably a better starting point.
Thinking like an engine, we realize a few things. First, the intake port has a larger cross section, which means that the intake flow velocity will be lower, which means that we probably want to close the intake valve a little sooner to avoid losing power to reversion. Decreasing intake duration will close the valve sooner, but it will also open the valve later, and since the usual problem on a 2 valve motor is not getting the intake open soon enough, maybe we should just advance the ICL. Now, our high flowing intake is filling the cylinder better at high RPM, which means that we'll have more exhaust gas volume, which means that we'll have more exhaust pumping losses, which means that we should think about opening the exhaust valve a bit sooner for earlier exhaust blowdown. So we increase exhaust duration ... but wait, we just advanced the cam for our intake side, so our exhaust valve is already opening sooner! So maybe we don't need more exhaust duration - in fact, maybe all we need to do is advance our existing cam a few degrees.
So we come up with a first try that looks like: 236/240/110 +5. This would be an unlikely first try if we think in terms of durations and LSAs, because it "looks odd" and doesn't match our preconceptions about "large split" being needed for low E/I ratios. But it is a very logical thing to try if you think in terms of valve events, and I'd say there is a better chance it would work than our larger split spec.
#32
FormerVendor
iTrader: (13)
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Originally Posted by Chicago Crew UnderBoss
ALL OF THAT and no recommendations for my motor which by the way will be running the latest and greatest TRICK FLOW 235 Heads ported by TEA!
COME ON GUYS, shoot me some cam specs that will make huge power throughout the entire rpm band on my new LME Built 430 CID LS7 MOTOR, that will power my 02 C5 Z06 which will see mostly street duty, some limited drag race duty and some ROAD RACING BABY!
![Driving](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_driving3.gif)
![Driving](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_driving3.gif)
![Chug! Chug! Chug!](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_chug.gif)
![Driving](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_driving3.gif)
COME ON GUYS, shoot me some cam specs that will make huge power throughout the entire rpm band on my new LME Built 430 CID LS7 MOTOR, that will power my 02 C5 Z06 which will see mostly street duty, some limited drag race duty and some ROAD RACING BABY!
![Driving](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_driving3.gif)
![Driving](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_driving3.gif)
![Happy](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_stretch.gif)
#35
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![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Originally Posted by Brian Tooley
You should have told the tax man to take a hike and built this thing ![Happy](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_stretch.gif)
![Happy](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_stretch.gif)
![Burnout](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_burnout.gif)
![Burnout](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_burnout.gif)
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#36
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
This one's 4 sale:
P/N 54-00011, J 0553-06
LS1 Gen III 97-up Roller: Custom Billet Roller from "Cam Motion"
Grind LS1 4020R/4018R R 107
Intake Exhaust
.715 .715 - Lift
266 270 @ .050 Duration
LSA 107, ICL 107
Good luck Bro.
P/N 54-00011, J 0553-06
LS1 Gen III 97-up Roller: Custom Billet Roller from "Cam Motion"
Grind LS1 4020R/4018R R 107
Intake Exhaust
.715 .715 - Lift
266 270 @ .050 Duration
LSA 107, ICL 107
Good luck Bro.
![Mr. Cool](https://ls1tech.com/forums/images/smilies/LS1Tech/gr_cool.gif)
#38
Race your car!
iTrader: (50)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
Originally Posted by americanmusl
P/N 54-00011, J 0553-06
LS1 Gen III 97-up Roller: Custom Billet Roller from "Cam Motion"
Grind LS1 4020R/4018R R 107
Intake Exhaust
.715 .715 - Lift
266 270 @ .050 Duration
LSA 107, ICL 107
LS1 Gen III 97-up Roller: Custom Billet Roller from "Cam Motion"
Grind LS1 4020R/4018R R 107
Intake Exhaust
.715 .715 - Lift
266 270 @ .050 Duration
LSA 107, ICL 107
good luck getting the hydraulic valvetrain to stay together with that cam... that thing is gonna be killing lifters like mad.
#39
TECH Fanatic
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Underboss, I think you should click that link at the bottom of Patrick G's signature that says custom camshaft help. He will recommend you a couple of different cams and give you a breakdown on why they will be good for your setup along with valve events, SCR, DCR, etc. I recently did it, don't have results yet, but I'm very confident in Patrick. They guy knows his stuff.
#40
TECH Junkie
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Why dont you talk to the people that actually have running 400-440 inch motors, as in they ET and trap we for their weight. Cars should be in the 9.8-10.3 range even at 3400-3600 lbs easy if they are making the dyno numbers some claim
They have the best idea, because they are already doing it.
JL you be surprised wht you can do with a hyd, were turning more than 650 lift to 8k even with big steel valves
They have the best idea, because they are already doing it.
JL you be surprised wht you can do with a hyd, were turning more than 650 lift to 8k even with big steel valves