50 degree valve seats in modern hot street builds: is it finally time?

[Warp Speed]

You missed the part where nitro2 said "Usually the greatest depression (relative to atmospheric pressure) will be part way down the intake stroke and it can be several psi at high rpm. Flowbench tests are typically in the vicinity of 1 psi, which is not nearly enough"

I addressed that when I said David apparently didn't reference atmospheric pressure.

What is it referenced to if not atmospheric pressure?

[hoffman900]

Ok Bob, I read your post twice, slept on it and read it again this morning. It appears as though all Clint is saying is that the graph posted didn't come from his software so David must have compiled the sensor data and fit it to the basic template, if you will, that matches all of the other charts and graphs in his books which allowed him to overlay several things on one chart.

David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.

What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.

Obviously not everyone sees it that way.

I believe the data did come from Clint's sensors, just it was formatted and published in David's format.

I don't doubt the data, but I think it is misleading.

Here is a pressure diagram from EPI-Eng referenced to atmosphere. The overall shape of the curves mimic all the simulated and measured (from Formula One, Moto GP, from Clint, and just about everything in between) referenced to atmosphere.



Red line is exhaust port pressure.
Navy Blue line is cylinder pressure.
Baby Blue line is intake port pressure.

Let's go back and look at one of David's.

Pressure graph 2.png

It's very clear David's graph is referenced to intake port pressure.

How do I know? On the EPI graph, look at the difference between intake port pressure and cylinder pressure. The greatest difference occurs at IVO and then at some point around TDC, they get much closer and stay that way (producing the level pressure curve until cylinder pressure overtakes port pressure). Intake port pressure actually rises higher than atmospheric through the (and higher than it does at IVO) to some point, typically a little before IVC, until the rapidly increasing cylinder pressure overtakes it.

When referenced to atmosphere, the cylinder never sees that much of a depression. At overlap, David's graph is the equivalent of measuring how far underground a basement is, not from the ground surface (atmospheric), but from the top of the roof (intake port pressure).

There is a book called, 'How to Lie with Statistics'. It was first written in 1954 but has subsequently been updated. When you want to look at data, the first thing you look at are graph axis and the data reference point. This is Statistics 101 stuff. Do I think David lied? Absolutely not, I'm only bringing that up because people do take data, tie it to a different reference point, to try to tell a different story for nefarious or political gains. Sometimes it's an accident (or misunderstanding) and there was zero malice. I don't work as one, but I was trained to be a scientist and to look at data. As a scientist you're trained to look for stuff like this.

I don't know what came first, David's low lift theories or this data, but he either published this to market and give credence to preexisting theories of his or he has based his low lift flow theories on incorrectly interpreting data. That's my 2 cents. David's a big boy, if he wants to chat about it like an adult (aka, not have 2/3 of his post be hyperbole), he can come here and do so. I don't think you or Gary are in a position to talk for him, especially on this. If you guys want to learn though, I’m all for helping out!

The thread where his graph was posted and Clint respond: https://www.speed-talk.com/forum/viewtopic.php?f=1&t=41433

[RevTheory]

I'm not going to try to talk for anybody; I was only trying to make sense of what he was getting at. And I'm absolutely not willing to call him dishonest or imply that he's willfully misleading people. I know some people foam at the mouth just waiting for him to say anything they can pounce on. I just want to make sure I fully grasp what everyone is saying whether it's a detailed point about one specific aspect or a broader picture.

There's nothing wrong with zeroing in on a particular aspect if you're trying to make a point and I'm pretty sure that nobody has ever implied that the exhaust will pull 1000 cfm through the carburetor at TDC so I try to take everything in the context it was written. I believe that to be the cylinder depression seen at TDC/low-lift vs the pumping phase with high-lift between the three sensors; not the top of the piston compared to atmosphere.
Again, I could certainly be looking at it wrong.

Having said that, David's writing style often leaves a door open and sometimes people just can't wait to drive a truck through it. Thanks for the graphs referencing atmosphere; I don't have any of those saved on a file for review.

[hoffman900]

I'm not going to try to talk for anybody; I was only trying to make sense of what he was getting at. And I'm absolutely not willing to call him dishonest or imply that he's willfully misleading people. I know some people foam at the mouth just waiting for him to say anything they can pounce on. I just want to make sure I fully grasp what everyone is saying whether it's a detailed point about one specific aspect or a broader picture.

There's nothing wrong with zeroing in on a particular aspect if you're trying to make a point and I'm pretty sure that nobody has ever implied that the exhaust will pull 1000 cfm through the carburetor at TDC so I try to take everything in the context it was written. I believe that to be the cylinder depression seen at TDC/low-lift vs the pumping phase with high-lift between the three sensors; not the top of the piston compared to atmosphere.
Again, I could certainly be looking at it wrong.

Having said that, David's writing style often leaves a door open and sometimes people just can't wait to drive a truck through it. Thanks for the graphs referencing atmosphere; I don't have any of those saved on a file for review.

Rev,

Good, we're on the same page then.

Everything has its place. Overlap is obviously important. Ignoring the numbers, David's graph does show the importance of the overlap portion's ability to get air moving, but that's all it pretty much does. It just starts the process. As pointed out, the space between the combustion chamber and piston top is very small at this point. So yes, the difference between intake pressure and the cylinder pressure are at the greatest here, and yes it kicks start the process of air moving into the chamber, but what it doesn't show is very little mass is trapped at this point. Partly because it's just starting the process, partly because the valve is opened very little, and partly because there is nowhere for it to go (except out the exhaust port). Too much of that and you end up with an over scavenge issue. Builders with hemispherical chambers (old Japanese and British motorcycles, Chrysler products, Alfa Romeos, air cooled Porsches, etc.) have all learned about this. This is why some of the racing hemi heads have little "dams" between the two and have offset valves. This is also why you sometimes see huge splits in duration on some of them (10-15* less exhaust duration).

There is a risk reward here. Nail the IVO and, in Harold's words you can "clean out the chamber and get air flowing". The problem is this will only occur over a narrow range of the entire powerband (when the intake is in the range it was tuned for ) and it's a razor's edge of having too much and causing reversion even where you didn't intend to have it. Because little mass is trapped, you can throw portions of it away to make a difference later on where you can actually retain the air/fuel mass. Overlap and low lift flow, to me, is one of those things it's better to be on the conservative side than to be aggressive.

There is an old saying in road racing for drivers, "slow in, fast out". There is more to gain on corner exit than entrance. Lots of truth to that. Think of that in terms of flow. Slow in and lose the risk of blowing the corner (reversion) to gain on the way out (inertia at later parts of the lift cycle). Obviously there is a balance. You can be slow in and slow out too.

[RevTheory]

I wonder if there's some magical lift point (L/D ratio, perhaps...) where the depression starts moving upstream and it makes more sense to start referencing atmosphere; .200 ish?

Edit: Looking at the charts, maybe TDC or shortly thereafter rather than valve lift. Either way, I like to be able to put raw data together from various points of view and build a pretty good working model.

Overlap and reversion is always a tricky little devil.

[Warp Speed]

I wonder if there's some magical lift point (L/D ratio, perhaps...) where the depression starts moving upstream and it makes more sense to start referencing atmosphere; .200 ish?

EVERYTHING is (Or should be) referenced to atmosphere. That IS the datum point for all sensors in the system. The intake and exhaust pressure sensors are initially referenced and set to atmosphere, and the cylinder sensors are "pinged" for reference to the intake sensor.

[RevTheory]

EVERYTHING is (Or should be) referenced to atmosphere. That IS the datum point for all sensors in the system. The intake and exhaust pressure sensors are initially referenced and set to atmosphere, and the cylinder sensors are "pinged" for reference to the intake sensor.

When looking at the overlap phase that seems about as accurate as judging the output of your new A/C window unit while you stand in another room with the door barely cracked open. Calibrated to atmosphere is fine, obviously.

Let's all try to be honest here rather than chomping at the bit to cry foul over anything you can think of because you don't like someone's personality.

[Warp Speed]

EVERYTHING is (Or should be) referenced to atmosphere. That IS the datum point for all sensors in the system. The intake and exhaust pressure sensors are initially referenced and set to atmosphere, and the cylinder sensors are "pinged" for reference to the intake sensor.

When looking at the overlap phase that seems about as accurate as judging the output of your new A/C window unit while you stand in another room with the door barely cracked open. Calibrated to atmosphere is fine, obviously.

Let's all try to be honest here rather than chomping at the bit to cry foul over anything you can think of because you don't like someone's personality.

My post was purely base from how a combustion system works, and how it is referenced and initially calibrated every day prior to start of testing. I did leave our that these sensors, and their initial calibration, along with an algorithm based from the engine rpm and stroke, is how tdc location is determined prior to testing. All are VERY critical, as small errors in any, can lead to large deviations in measured results.
Your last comment needs to be headed by yourself also, as well the others that have differing views!
NOTHING technical I have posted, is based on my personal view of someone or their personality, but based on the testing we do every day!

[RevTheory]

Hey Bob, where do you reckon (technical term ) "0" is on the graph you posted?

[hoffman900]

Hey Bob, where do you reckon (technical term ) "0" is on the graph you posted?

Just below the 15. I'm not sure what the axis gradation is, so just look below the 15.

1 atmosphere is 14.7 psia. This assuming sea level of course.

[RevTheory]

Thanks. I didn't know if it was the line below 15 or halfway or what.

[CGT]

not have 2/3 of his post be hyperbole),

Ive been recently blocking members that habitually contribute extremely long posts that go no where, or add nothing but opinion posing as fact. It really does clean up things in threads like this

[GARY C]

Ok Bob, I read your post twice, slept on it and read it again this morning. It appears as though all Clint is saying is that the graph posted didn't come from his software so David must have compiled the sensor data and fit it to the basic template, if you will, that matches all of the other charts and graphs in his books which allowed him to overlay several things on one chart.

David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.

What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.

Obviously not everyone sees it that way.

I believe the data did come from Clint's sensors, just it was formatted and published in David's format.

I don't doubt the data, but I think it is misleading.

Here is a pressure diagram from EPI-Eng referenced to atmosphere. The overall shape of the curves mimic all the simulated and measured (from Formula One, Moto GP, from Clint, and just about everything in between) referenced to atmosphere.



Red line is exhaust port pressure.
Navy Blue line is cylinder pressure.
Baby Blue line is intake port pressure.

Let's go back and look at one of David's.

Pressure graph 2.png

It's very clear David's graph is referenced to intake port pressure.

How do I know? On the EPI graph, look at the difference between intake port pressure and cylinder pressure. The greatest difference occurs at IVO and then at some point around TDC, they get much closer and stay that way (producing the level pressure curve until cylinder pressure overtakes port pressure). Intake port pressure actually rises higher than atmospheric through the (and higher than it does at IVO) to some point, typically a little before IVC, until the rapidly increasing cylinder pressure overtakes it.

When referenced to atmosphere, the cylinder never sees that much of a depression. At overlap, David's graph is the equivalent of measuring how far underground a basement is, not from the ground surface (atmospheric), but from the top of the roof (intake port pressure).

There is a book called, 'How to Lie with Statistics'. It was first written in 1954 but has subsequently been updated. When you want to look at data, the first thing you look at are graph axis and the data reference point. This is Statistics 101 stuff. Do I think David lied? Absolutely not, I'm only bringing that up because people do take data, tie it to a different reference point, to try to tell a different story for nefarious or political gains. Sometimes it's an accident (or misunderstanding) and there was zero malice. I don't work as one, but I was trained to be a scientist and to look at data. As a scientist you're trained to look for stuff like this.

I don't know what came first, David's low lift theories or this data, but he either published this to market and give credence to preexisting theories of his or he has based his low lift flow theories on incorrectly interpreting data. That's my 2 cents. David's a big boy, if he wants to chat about it like an adult (aka, not have 2/3 of his post be hyperbole), he can come here and do so. I don't think you or Gary are in a position to talk for him, especially on this. If you guys want to learn though, I’m all for helping out!

The thread where his graph was posted and Clint respond: https://www.speed-talk.com/forum/viewtopic.php?f=1&t=41433

Could the confusion be that David is referencing port velocity as opposed to port pressure? I am not a graph guy so it's hard to compare with no ref numbers on your chart but it looks like they are referencing two different things.

I only said what I said because of the conversations I had with David before he contacted Clint and the tests he was involved in with others using TFX equipment.

[hoffman900]

Ok Bob, I read your post twice, slept on it and read it again this morning. It appears as though all Clint is saying is that the graph posted didn't come from his software so David must have compiled the sensor data and fit it to the basic template, if you will, that matches all of the other charts and graphs in his books which allowed him to overlay several things on one chart.

David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.

What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.

Obviously not everyone sees it that way.

I believe the data did come from Clint's sensors, just it was formatted and published in David's format.

I don't doubt the data, but I think it is misleading.

Here is a pressure diagram from EPI-Eng referenced to atmosphere. The overall shape of the curves mimic all the simulated and measured (from Formula One, Moto GP, from Clint, and just about everything in between) referenced to atmosphere.



Red line is exhaust port pressure.
Navy Blue line is cylinder pressure.
Baby Blue line is intake port pressure.

Let's go back and look at one of David's.

Pressure graph 2.png

It's very clear David's graph is referenced to intake port pressure.

How do I know? On the EPI graph, look at the difference between intake port pressure and cylinder pressure. The greatest difference occurs at IVO and then at some point around TDC, they get much closer and stay that way (producing the level pressure curve until cylinder pressure overtakes port pressure). Intake port pressure actually rises higher than atmospheric through the (and higher than it does at IVO) to some point, typically a little before IVC, until the rapidly increasing cylinder pressure overtakes it.

When referenced to atmosphere, the cylinder never sees that much of a depression. At overlap, David's graph is the equivalent of measuring how far underground a basement is, not from the ground surface (atmospheric), but from the top of the roof (intake port pressure).

There is a book called, 'How to Lie with Statistics'. It was first written in 1954 but has subsequently been updated. When you want to look at data, the first thing you look at are graph axis and the data reference point. This is Statistics 101 stuff. Do I think David lied? Absolutely not, I'm only bringing that up because people do take data, tie it to a different reference point, to try to tell a different story for nefarious or political gains. Sometimes it's an accident (or misunderstanding) and there was zero malice. I don't work as one, but I was trained to be a scientist and to look at data. As a scientist you're trained to look for stuff like this.

I don't know what came first, David's low lift theories or this data, but he either published this to market and give credence to preexisting theories of his or he has based his low lift flow theories on incorrectly interpreting data. That's my 2 cents. David's a big boy, if he wants to chat about it like an adult (aka, not have 2/3 of his post be hyperbole), he can come here and do so. I don't think you or Gary are in a position to talk for him, especially on this. If you guys want to learn though, I’m all for helping out!

The thread where his graph was posted and Clint respond: https://www.speed-talk.com/forum/viewtopic.php?f=1&t=41433

Could the confusion be that David is referencing port velocity as opposed to port pressure? I am not a graph guy so it's hard to compare with no ref numbers on your chart but it looks like they are referencing two different things.

I only said what I said because of the conversations I had with David before he contacted Clint and the tests he was involved in with others using TFX equipment.

Velocity is calculated from differential in pressure (among other things, like density).

His port and and seat velocities are weird. Port velocity will never be higher than the seat. The port will be a more subdued profile than at the seat.

[GARY C]

I believe the data did come from Clint's sensors, just it was formatted and published in David's format.

I don't doubt the data, but I think it is misleading.

Here is a pressure diagram from EPI-Eng referenced to atmosphere. The overall shape of the curves mimic all the simulated and measured (from Formula One, Moto GP, from Clint, and just about everything in between) referenced to atmosphere.



Red line is exhaust port pressure.
Navy Blue line is cylinder pressure.
Baby Blue line is intake port pressure.

Let's go back and look at one of David's.


It's very clear David's graph is referenced to intake port pressure.

How do I know? On the EPI graph, look at the difference between intake port pressure and cylinder pressure. The greatest difference occurs at IVO and then at some point around TDC, they get much closer and stay that way (producing the level pressure curve until cylinder pressure overtakes port pressure). Intake port pressure actually rises higher than atmospheric through the (and higher than it does at IVO) to some point, typically a little before IVC, until the rapidly increasing cylinder pressure overtakes it.

When referenced to atmosphere, the cylinder never sees that much of a depression. At overlap, David's graph is the equivalent of measuring how far underground a basement is, not from the ground surface (atmospheric), but from the top of the roof (intake port pressure).

There is a book called, 'How to Lie with Statistics'. It was first written in 1954 but has subsequently been updated. When you want to look at data, the first thing you look at are graph axis and the data reference point. This is Statistics 101 stuff. Do I think David lied? Absolutely not, I'm only bringing that up because people do take data, tie it to a different reference point, to try to tell a different story for nefarious or political gains. Sometimes it's an accident (or misunderstanding) and there was zero malice. I don't work as one, but I was trained to be a scientist and to look at data. As a scientist you're trained to look for stuff like this.

I don't know what came first, David's low lift theories or this data, but he either published this to market and give credence to preexisting theories of his or he has based his low lift flow theories on incorrectly interpreting data. That's my 2 cents. David's a big boy, if he wants to chat about it like an adult (aka, not have 2/3 of his post be hyperbole), he can come here and do so. I don't think you or Gary are in a position to talk for him, especially on this. If you guys want to learn though, I’m all for helping out!

The thread where his graph was posted and Clint respond: https://www.speed-talk.com/forum/viewtopic.php?f=1&t=41433

Could the confusion be that David is referencing port velocity as opposed to port pressure? I am not a graph guy so it's hard to compare with no ref numbers on your chart but it looks like they are referencing two different things.

I only said what I said because of the conversations I had with David before he contacted Clint and the tests he was involved in with others using TFX equipment.

Velocity is calculated from differential in pressure (among other things, like density).

I just had a brief conversation with David, this is not data from Clint's equipment, I don't know how it was set up or calculated but he's referencing flow and velocity not pressure.

If you look it up in the book Brad referenced it's dealing with flow procedures and used to show why a fixed 28" is not any where near what is going on in a working engine.