valve timing events??

[hoffman900]

The exhaust valve isn’t stopping the flow, rising cylinder pressure does. If you do it right, at peak power, the the port flow is nearly stopped by the time the exhaust valve closes. The port is already beginning to slow down before BDC.

To quote the late MadBill from like 15-18 years ago, “if gasses slam into the back of the intake valve, you closed too early”.

1D7C2F0D-728A-435A-B5AF-76B68C86868E.jpeg

Look at peak location of mass flow at the valve seat and carb booster location.

Taken from the other thread:

Cylinder pressure bottoms out well before BDC and port pressure mirrors its rise.

Bob,
Did I miss a post? When did this happen? The last time I had contact with Bill was about a year ago, and he was still dealing with the lose of his wife.

Stan

Stan, he passed just before the holidays: viewtopic.php?t=66121

[ClassAct]

The exhaust valve isn’t stopping the flow, rising cylinder pressure does. If you do it right, at peak power, the the port flow is nearly stopped by the time the exhaust valve closes. The port is already beginning to slow down before BDC.

To quote the late MadBill from like 15-18 years ago, “if gasses slam into the back of the intake valve, you closed too early”.

1D7C2F0D-728A-435A-B5AF-76B68C86868E.jpeg

Look at peak location of mass flow at the valve seat and carb booster location.

Taken from the other thread:

Cylinder pressure bottoms out well before BDC and port pressure mirrors its rise.

Bob,
Did I miss a post? When did this happen? The last time I had contact with Bill was about a year ago, and he was still dealing with the lose of his wife.

Stan

Stan, he passed just before the holidays: viewtopic.php?t=66121

Damn, I didn't see that either. MB will be missed.

[Erland Cox]

I'm referring to air/fuel movement established into the cylinder and the inertia it has, not the state of the inlet port at valve opening.

Do you mean the Inertia from the accelerated fuel and air in the runner when the piston is reversing after BDC and the inlet valve is starting to close?

Erland

No, not a BDC. In regard to your statement on page 2

If you look at graphs of piston velocity and intake port velocity the intake gases are moving when the piston stands still.
This is work done from the rarefaction wave from the exhaust port and some from the compression wave in the intake port.
The idea is using this wave energy to move gas into the cylinder, to keep the intake velocity up until the piston has enough
velocity to pull on the intake without loosing velocity.
An exhaust valve that closes before the piston has velocity will slow down the intake velocity to stop and go.
Then the intake port will resume flowing when the piston has picked up velocity.

The intake gasses are moving when the piston stands still. Intake gasses have mass and with the momentum established with this movement therefore has inertia. An external sufficient force is required to overcome that inertia of the incoming air/fuel if it is to slow or stop moving, not just the absence of the force that created the movement. The rarefaction wave has created sufficient force to get the air/fuel charge in the intake port moving but I can't see the closing of the exhaust valve is sufficient enough force to overcome any inertia generated by its movement into the cylinder creating a stop/go situation, especially with the time period involved within these few degrees of crank rotation. On the other hand if the air/fuel charge quantity that is pulled into the chamber by the exhaust wave is so tiny that it is able to stop and go, its contribution to the overall density of the charge would be so small then if there is a situation of a second 'go' per induction cycle then that second 'go' is the one that matters and starts pulling real quantities of air/fuel charge. Maybe that's why UDHarold doesn't mention it. If I'm wrong I'll learn something.

Yes but this is in the beginning when the gas is accelerated by a pressure difference.
If that pressure difference is lost so is the velocity.
That is why I wrote that the Inertia works backwards from what people believe.
Resistance to movement creates a pressure difference and this pressure difference does the movement.
The pressure difference amplitude comes from the resistance to movement and that is depending on velocity and reflections along the path.
I believe that the inertia itself is only a little part of the filling.

Erland

[Erland Cox]

I am saddened by the loss of Bill.
He will be missed on this community.

Erland

[Stan Weiss]

The exhaust valve isn’t stopping the flow, rising cylinder pressure does. If you do it right, at peak power, the the port flow is nearly stopped by the time the exhaust valve closes. The port is already beginning to slow down before BDC.

To quote the late MadBill from like 15-18 years ago, “if gasses slam into the back of the intake valve, you closed too early”.

1D7C2F0D-728A-435A-B5AF-76B68C86868E.jpeg

Look at peak location of mass flow at the valve seat and carb booster location.

Taken from the other thread:

Cylinder pressure bottoms out well before BDC and port pressure mirrors its rise.

Bob,
Did I miss a post? When did this happen? The last time I had contact with Bill was about a year ago, and he was still dealing with the lose of his wife.

Stan

Stan, he passed just before the holidays: viewtopic.php?t=66121

Bob,
Thank you. I did miss that.

RIP Bill, you will be missed

Stan

[HQM383]

Do you mean the Inertia from the accelerated fuel and air in the runner when the piston is reversing after BDC and the inlet valve is starting to close?

Erland

No, not a BDC. In regard to your statement on page 2

If you look at graphs of piston velocity and intake port velocity the intake gases are moving when the piston stands still.
This is work done from the rarefaction wave from the exhaust port and some from the compression wave in the intake port.
The idea is using this wave energy to move gas into the cylinder, to keep the intake velocity up until the piston has enough
velocity to pull on the intake without loosing velocity.
An exhaust valve that closes before the piston has velocity will slow down the intake velocity to stop and go.
Then the intake port will resume flowing when the piston has picked up velocity.

The intake gasses are moving when the piston stands still. Intake gasses have mass and with the momentum established with this movement therefore has inertia. An external sufficient force is required to overcome that inertia of the incoming air/fuel if it is to slow or stop moving, not just the absence of the force that created the movement. The rarefaction wave has created sufficient force to get the air/fuel charge in the intake port moving but I can't see the closing of the exhaust valve is sufficient enough force to overcome any inertia generated by its movement into the cylinder creating a stop/go situation, especially with the time period involved within these few degrees of crank rotation. On the other hand if the air/fuel charge quantity that is pulled into the chamber by the exhaust wave is so tiny that it is able to stop and go, its contribution to the overall density of the charge would be so small then if there is a situation of a second 'go' per induction cycle then that second 'go' is the one that matters and starts pulling real quantities of air/fuel charge. Maybe that's why UDHarold doesn't mention it. If I'm wrong I'll learn something.

Yes but this is in the beginning when the gas is accelerated by a pressure difference.
If that pressure difference is lost so is the velocity.
That is why I wrote that the Inertia works backwards from what people believe.
Resistance to movement creates a pressure difference and this pressure difference does the movement.
The pressure difference amplitude comes from the resistance to movement and that is depending on velocity and reflections along the path.
I believe that the inertia itself is only a little part of the filling.

Erland

“....when the gas is accelerated by a pressure difference.”

inertia
a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.

I see both of those states of inertia in play during overlap as the cylinder begins to fill with air/fuel change and it is accelerated by a pressure difference.

[Erland Cox]

But what happens when that pressure difference is interrupted?
Doesn´t that make that intake stroke loose a lot of its filling possibilities?

Erland

[HQM383]

But what happens when that pressure difference is interrupted?
Doesn´t that make that intake stroke loose a lot of its filling possibilities?

Erland

I wouldn't discount the possibility, but the timing of all aspects - valves and piston movement would be way out to sea to lose a lot of filling possibilities would they not?

Is there enough time to have an influence of any measured consequence more than that of margin of error stuff? If the pressure differential that created the movement and acceleration of air/fuel initially from the port has subsided then a period of time will be taken for the air/fuel to decelerate and lose momentum if there is no other force acting upon it. The piston may well have taken over depression duties part way through that air/fuel deceleration period. But again at various rpm's it would change due to the time factor. You would be better at the math than me to work out how much time is involved in the crank degree window and rpm you are considering. I certainly agree it is worth exploring to find what can be manipulated to find more output.


Good conversation to get the grey matter working.

[Erland Cox]

I have one test car and what is most important is that it must be fast on track.
Right now I have this intake lobe: Total duration 364 Rated duration 299 Duration at 1mm 281 Duration at 0,050" 275 and lift.16.0mm
My exhaust lobe is:364 300 280 274 14.5 and the lobe separation is 105 degrees.
I can rev forever. Maximum hp is just above 270hp at 7000 rpm but I have more than 250 hp from 6300 to 8300.
This makes me think that I have to much exhaust time area.
So with the camshaft I can either go down in duration or use a smaller lobe separation ans open and close exhaust later.
I do not have a very high hp per liter but maybe it is OK for 7000 rpm+ 2540cc 106,3 hp per liter. 294 Nm:s 14,55 bar Bmep.
I believe the exhaust gives bmep and hp away.
Cam is in at 101 on intake and 109 on exhaust.
That means that exhaust is closing to rated duration at 41 degrees ATDC.
Intake is opening at 48,5 degrees BTDC.
A 4 cylinder with 180 degree exhaust intervals need less exhaust duration than a V8 and often have reversed split on the curation with less exhaust duration.
My cam has almost the same duration in and out but comparing to an American circle track cam with the same intake duration ny exhaust closes earlier.
If I would go to a 101 degrees lobe separation my exhaust would open and close 8 degrees later.
I will have to test to see what that does.

Erland