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.

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

Originally Posted by MPM IV

I don't have a recommendation, but I did PM you a couple of questions.

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.

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.

Originally Posted by Chicago Crew UnderBoss

OH, take a chance brother!

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!

Originally Posted by Brian Tooley

You should have told the tax man to take a hike and built this thing

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