Intake closing

[englertracing]

Some builders (certainly one in particular) state that the LSA is the single most important camshaft spec for greatest torque output all else being equal (as in RPM ) . Tailor the valve events to fit around that. Which is pretty simple when you think about. Say a 108 LSA is best. Then an IVC that's suitable. And fall in from there.
I'm not saying that this is how you spec a cam, I'm just saying.

Lsa isn't even spoken about on twin cam engines.....

[skinny z]

Some builders (certainly one in particular) state that the LSA is the single most important camshaft spec for greatest torque output all else being equal (as in RPM ) . Tailor the valve events to fit around that. Which is pretty simple when you think about. Say a 108 LSA is best. Then an IVC that's suitable. And fall in from there.
I'm not saying that this is how you spec a cam, I'm just saying.

Lsa isn't even spoken about on twin cam engines.....

Perhaps I should have further defined the definition...

So where does LSA enter into all of this? Maybe we can stick two plane crank V8's for apples to apples?

Make that two plane crank V8's with one cam.

Because LSA in twin cammed engines is why there are twin cammed engines. And I'm assuming twin cams per cylinder bank yes? Otherwise in a SOHC V8, despite having two cams, we're right back to square one.

[hoffman900]

LSA is pretty meaningless on all engines. LSA tells you nothing.

Basically you install it on the prescribed intake center line and LSA is the difference between the ICL and ECL, but short of custom billet cores, most are usually stuck with what is available with cast core sources.

But again, the events matter, this is what is great about DOHC per bank. You can move the exhaust cam and intake cam independently of each other and on variable valve train systems, they can move independent of each other across the rpm sweep and depending on load. When you move a single cam, the relationship between the intake and exhaust stays the same as the lobes are fixed in relation to each other, so you move all four events.

Furthermore, I'm not a believer in that on event is any more important than the other. Not worth retyping everything we covered here,but give this thread a read.viewtopic.php?f=1&t=51760

[skinny z]

LSA is pretty meaningless on all engines. LSA tells you nothing.

Basically you install it on the prescribed intake center line and LSA is the difference between the ICL and ECL, but short of custom billet cores, most are usually stuck with what is available with cast core sources.

But again, the events matter, this is what is great about DOHC per bank. You can move the exhaust cam and intake cam independently of each other and on variable valve train systems, they can move independent of each other across the rpm sweep and depending on load. When you move a single cam, the relationship between the intake and exhaust stays the same as the lobes are fixed in relation to each other, so you move all four events.

Furthermore, I'm not a believer in that on event is any more important than the other. Not worth retyping everything we covered here,but give this thread a read. viewtopic.php?t=51760&start=60

Sticking with a single cam engine, I can't see how LSA is meaningless. I will agree with you that not [sic] "any one event is any more important than the other" but the LSA is most certainly an important element. Having both valves open at the same time...it's proven that all sorts of shit happens when that's going on. Some beneficial. Others, not so much.
I'm not here to argue as my experience doesn't come close to others but the evidence supports my position in one way or another.

[hoffman900]

LSA is pretty meaningless on all engines. LSA tells you nothing.

Basically you install it on the prescribed intake center line and LSA is the difference between the ICL and ECL, but short of custom billet cores, most are usually stuck with what is available with cast core sources.

But again, the events matter, this is what is great about DOHC per bank. You can move the exhaust cam and intake cam independently of each other and on variable valve train systems, they can move independent of each other across the rpm sweep and depending on load. When you move a single cam, the relationship between the intake and exhaust stays the same as the lobes are fixed in relation to each other, so you move all four events.

Furthermore, I'm not a believer in that on event is any more important than the other. Not worth retyping everything we covered here,but give this thread a read. viewtopic.php?t=51760&start=60

Sticking with a single cam engine, I can't see how LSA is meaningless. I will agree with you that not [sic] "any one event is any more important than the other" but the LSA is most certainly an important element. Having both valves open at the same time...it's proven that all sorts of shit happens when that's going on. Some beneficial. Others, not so much.
I'm not here to argue as my experience doesn't come close to others but the evidence supports my position in one way or another.

The evidence only supports your position due to half a century of being taught about LSA by magazines and aftermarket cam manufacturers, builders "trust it" and have built rules of thumb from it, but from a design engineering perspective, it has no use.

[skinny z]

LSA is pretty meaningless on all engines. LSA tells you nothing.

Basically you install it on the prescribed intake center line and LSA is the difference between the ICL and ECL, but short of custom billet cores, most are usually stuck with what is available with cast core sources.

But again, the events matter, this is what is great about DOHC per bank. You can move the exhaust cam and intake cam independently of each other and on variable valve train systems, they can move independent of each other across the rpm sweep and depending on load. When you move a single cam, the relationship between the intake and exhaust stays the same as the lobes are fixed in relation to each other, so you move all four events.

Furthermore, I'm not a believer in that on event is any more important than the other. Not worth retyping everything we covered here,but give this thread a read. viewtopic.php?t=51760&start=60

Sticking with a single cam engine, I can't see how LSA is meaningless. I will agree with you that not [sic] "any one event is any more important than the other" but the LSA is most certainly an important element. Having both valves open at the same time...it's proven that all sorts of shit happens when that's going on. Some beneficial. Others, not so much.
I'm not here to argue as my experience doesn't come close to others but the evidence supports my position in one way or another.

The evidence only supports your position because due to half a century of being taught about LSA by magazines and aftermarket cam manufacturers, builders "trust it" and have built rules of thumb from it, but from a design engineering perspective, it has no use.

Fair enough.
Although I take little from magazines or cam manufacturers. I have education elsewhere.
I have nothing but respect from those that design and engineer the components I'm after. If you're one of them, then my hat's off to you.

[hoffman900]

Sticking with a single cam engine, I can't see how LSA is meaningless. I will agree with you that not [sic] "any one event is any more important than the other" but the LSA is most certainly an important element. Having both valves open at the same time...it's proven that all sorts of shit happens when that's going on. Some beneficial. Others, not so much.
I'm not here to argue as my experience doesn't come close to others but the evidence supports my position in one way or another.

The evidence only supports your position because due to half a century of being taught about LSA by magazines and aftermarket cam manufacturers, builders "trust it" and have built rules of thumb from it, but from a design engineering perspective, it has no use.

Fair enough.
Although I take little from magazines or cam manufacturers. I have education elsewhere.

LSA = (Intake Centerline + Exhaust Centerline)/2 . 100 ICL and 112ECL is 106 LSA as is 104 ICL and 108 ECL, and so would 106 ICL and 106 ECL. Those cams would run completely different. If the valve lift profiles are asymmetrical, they would all be different still.

[skinny z]

The evidence only supports your position because due to half a century of being taught about LSA by magazines and aftermarket cam manufacturers, builders "trust it" and have built rules of thumb from it, but from a design engineering perspective, it has no use.

Fair enough.
Although I take little from magazines or cam manufacturers. I have education elsewhere.

LSA = (Intake Centerline + Exhaust Centerline)/2 . 100 ICL and 112ECL is 106 LSA as is 104 ICL and 108 ECL, and so would 106 ICL and 106 ECL. Those cams would run completely different. If the valve lift profiles are asymmetrical, they would all be different still.

You've changed the ICL. Change the LSA but keep the ICL the same. What do you get? Probably the same cranking compression no?

[hoffman900]

Fair enough.
Although I take little from magazines or cam manufacturers. I have education elsewhere.

LSA = (Intake Centerline + Exhaust Centerline)/2 . 100 ICL and 112ECL is 106 LSA as is 104 ICL and 108 ECL, and so would 106 ICL and 106 ECL. Those cams would run completely different. If the valve lift profiles are asymmetrical, they would all be different still.

You've changed the ICL. Change the LSA the same but keep the ICL the same. What do you get? Probably the same cranking compression no?

I don't think I ever looked at cranking compression and "dynamic" compression as the magazines have taught it is wrong, because dynamic compression needs to be thought of as pressure on a running engine, and it varies with load and rpm. Changing the LSA but holding the IVC the same means you are moving the ECL, so what you get is you have changed the ability to evacuate the cylinder and changed the overlap area / shape, so what the engine "sees" at IVO is different, and because that is different, what is happening at IVC is now different in terms of pressure delta between the cylinder and intake port. It would be a totally different running engine.

Harold was old fashioned and I doubt he saw pressure data until well in his twilight years, but he understood this from very early on:

The intake valve closing point mainly tells where the intake valve closes.
Get your favorite cam grinder to grind 2 cams with the identical profiles, but with TWO different LSAs, say 106 and 108, or 110 and 112.
Install one cam in the engine, then dyno it.
Install the other cam on the IDENTICAL intake centerline, so that opening and CLOSING points are the same for both cams.
The cams will have different cranking compressions, different power curves. This is not to say one is better than the other, only different.
What effects the REAL dynamic compression is HOW MUCH air and gas is in the cylinder when the intake valve closes, not at what degree ABDC the valve closes.
The different exhaust opening points affect the amount of back pressure, ie, reversion, that is present when the intake valve opens BTDC. The amount of reversion affects the rate of cylinder filling on the intake stroke, and the amount of air and gas in the cylinder when the intake valve closes. This is what gives you the actual Dynamic Compression. The operative word is DYNAMIC.
Other cam designers may differ in opinion.

UDHarold

Remember, everything that happens before effects the present, and with load / rpm changing, it's all going to change constantly.This also assumes an infinitely stiff valve train, so that very carefully dialed in camshaft isn't actually going to open and close at the same point through the sweep, especially in a pushrod system.

[skinny z]

LSA = (Intake Centerline + Exhaust Centerline)/2 . 100 ICL and 112ECL is 106 LSA as is 104 ICL and 108 ECL, and so would 106 ICL and 106 ECL. Those cams would run completely different. If the valve lift profiles are asymmetrical, they would all be different still.

You've changed the ICL. Change the LSA the same but keep the ICL the same. What do you get? Probably the same cranking compression no?

I don't think I ever looked at cranking compression and "dynamic" compression as the magazines have taught it is wrong, because dynamic compression needs to be thought of as pressure on a running engine, and it varies with load and rpm. Changing the LSA but holding the IVC the same means you are moving the ECL, so what you get is you have changed the ability to evacuate the cylinder, so what the engine "sees" at IVO is different, and because that is different, what is happening at IVC is now different in terms of pressure delta between the cylinder and intake port.

Harold was old fashioned and I doubt he saw pressure data until well in his twilight years, but he understood this from very early on:

The intake valve closing point mainly tells where the intake valve closes.
Get your favorite cam grinder to grind 2 cams with the identical profiles, but with TWO different LSAs, say 106 and 108, or 110 and 112.
Install one cam in the engine, then dyno it.
Install the other cam on the IDENTICAL intake centerline, so that opening and CLOSING points are the same for both cams.
The cams will have different cranking compressions, different power curves. This is not to say one is better than the other, only different.
What effects the REAL dynamic compression is HOW MUCH air and gas is in the cylinder when the intake valve closes, not at what degree ABDC the valve closes.
The different exhaust opening points affect the amount of back pressure, ie, reversion, that is present when the intake valve opens BTDC. The amount of reversion affects the rate of cylinder filling on the intake stroke, and the amount of air and gas in the cylinder when the intake valve closes. This is what gives you the actual Dynamic Compression. The operative word is DYNAMIC.
Other cam designers may differ in opinion.

UDHarold

Remember, everything that happens before effects the present, and with load / rpm changing, it's all going to change constantly.This also assumes an infinitely stiff valve train, so that very carefully dialed in camshaft isn't actually going to open and close at the same point through the sweep, especially in a pushrod system.

I understand and appreciate all of the above Mr H. And thanks for that.
Yes, I understand the failing of dynamic compression as a modelling tool and what happens when the engine is at RPM. So much so that I also understand how limited I am in that knowledge.
What I will do in the not too distant future is have this very discussion with respect to my own engine project. Short block and heads are determined. Next up is the cam spec and engine application. LSA might be a hot topic as that engine application is still up in the air.
Hope to see you there.
Thanks again.

[HQM383]

....What effects the REAL dynamic compression is HOW MUCH air and gas is in the cylinder when the intake valve closes, not at what degree ABDC the valve closes....

UDHarold

So considering Harold’s statement above and this from another thread:

A volume of air can exist at various pressures, which will determine density, and therefore MASS.

An internal combustion engine depends entirely on AIR and FUEL MASS, never volume.

For volume to have any meaning, we must know its density. Volume is a static metric, a space.

Is an attempt to calculate dynamic compression an exercise in futility if using swept volume without knowledge of density and mass?

[Tom68]

Is an attempt to calculate dynamic compression an exercise in futility if using swept volume without knowledge of density and mass?

No because at low speed open throttle you know the cylinder is full for the volume it has after inlet closing.

The variations of course occur as speed goes up and also with throttling.

[Geoff2]

[1] LSA tells you nothing? Hmm. It tells you in crank degrees where each valve is at max lift. Which allows to calculate where the piston is in the bore; and whether that might be the best place for it be for the respective function of the each valve.
[2] Even when the LSA is not quoted, it can be calculated from the timing numbers. Every IC 4 stroke engine is going to have a LSA, whether it has one or two cams.

[juuhanaa]

[1] LSA tells you nothing? Hmm. It tells you in crank degrees where each valve is at max lift. Which allows to calculate where the piston is in the bore; and whether that might be the best place for it be for the respective function of the each valve.
[2] Even when the LSA is not quoted, it can be calculated from the timing numbers. Every IC 4 stroke engine is going to have a LSA, whether it has one or two cams.

1 and 2, yes. Thats why saying LSA is a result of cam timing events is correct.

Problem 1: too many LSA topics
Problem 2: cant find topic how to adress low lift flow
Problem 3: i need a cam doctor to measure my V8 camshaft, because i dont know what the cam is.



-juhana

[hoffman900]

[1] LSA tells you nothing? Hmm. It tells you in crank degrees where each valve is at max lift. Which allows to calculate where the piston is in the bore; and whether that might be the best place for it be for the respective function of the each valve.
[2] Even when the LSA is not quoted, it can be calculated from the timing numbers. Every IC 4 stroke engine is going to have a LSA, whether it has one or two cams.

1) That’s what Lobe Centerlines tell you, not LSA, and why does it tell you best place? LSA is (ICL+ECL)/2. It has no relation to crank position.
2) I know. I literally posted the equation above.

Also centerlines get clouded when dealing with asymmetric valve lift curves.