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

[hoffman900]

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.

His Y-axis shows pressure. Velocity is caluclated from pressure. With zero delta between the two, you have no flow (velocity is the measured flow (speed) with direction).

Also, see my post above. Port velocity will almost never be higher than seat velocity. Port velocity will follow seat velocity but be more subdued.

[GARY C]

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.

His Y-axis shows pressure. Velocity is caluclated from pressure. With zero delta between the two, you have no flow (velocity is the measured flow (speed) with direction).

Also, see my post above. Port velocity will almost never be higher than seat velocity. Port velocity will follow seat velocity but be more subdued.

Like I said, I don't know how the equipment was set up and I have never recorded data from a running engine. I just wanted to clarify that it was not Clint's equipment.

[GARY C]

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.

His Y-axis shows pressure. Velocity is caluclated from pressure. With zero delta between the two, you have no flow (velocity is the measured flow (speed) with direction).

Also, see my post above. Port velocity will almost never be higher than seat velocity. Port velocity will follow seat velocity but be more subdued.

Another thing I noticed is you are referencing atmosphere and he is using inches of water, not sure how that correlates or if different sensors measure different ways? Just an observation.

[hoffman900]

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.

His Y-axis shows pressure. Velocity is caluclated from pressure. With zero delta between the two, you have no flow (velocity is the measured flow (speed) with direction).

Also, see my post above. Port velocity will almost never be higher than seat velocity. Port velocity will follow seat velocity but be more subdued.

Another thing I noticed is you are referencing atmosphere and he is using inches of water, not sure how that correlates or if different sensors measure different ways? Just an observation.

They're just units.

Atmospheric pressure )at sea level) is:
1013.25mbar
101.325kPa
1.01325bar
760mmHg
29.92inH2O
14.696psi

For the valve lift in David's graph, he just multiplied valve lift by 100 (ex: .450 becomes 450).

[Rick360]

Atmospheric pressure )at sea level) is:
1013.25mbar
101.325kPa
1.01325bar
760mmHg
29.92inH2O
14.696psi

For the valve lift in David's graph, he just multiplied valve lift by 100 (ex: .450 becomes 450).

29.92 inHg
406.784 inH2O

Rick

[hoffman900]

Atmospheric pressure )at sea level) is:
1013.25mbar
101.325kPa
1.01325bar
760mmHg
29.92inH2O
14.696psi

For the valve lift in David's graph, he just multiplied valve lift by 100 (ex: .450 becomes 450).

29.92 inHg
406.784 inH2O

Rick

oops I forgot flowbenches are that close to operating to a blackhole.

Gary,

I'm sure David is reading this, but ask him

1) Where were the port transducers located?
2) What was the cylinder pressure referenced to?
3) At what point on the power curve was this snapshot taken from (peak torque, peak horsepower, etc.)?

Just curious to know is all.

[GARY C]

Atmospheric pressure )at sea level) is:
1013.25mbar
101.325kPa
1.01325bar
760mmHg
29.92inH2O
14.696psi

For the valve lift in David's graph, he just multiplied valve lift by 100 (ex: .450 becomes 450).

29.92 inHg
406.784 inH2O

Rick

oops I forgot flowbenches are that close to operating to a blackhole.

Gary,

I'm sure David is reading this, but ask him

1) Where were the port transducers located?
2) What was the cylinder pressure referenced to?
3) At what point on the power curve was this snapshot taken from (peak torque, peak horsepower, etc.)?

Just curious to know is all.

I will try to talk to him next week of if he's reading it maybe he will respond.

so what is the cylinder pressure drop showing on your graph in h2o?

BTW, if it's in reference to flow benches and flow bench testing is that a bad thing to show the difference between a flow bench and an actual engine?

[hoffman900]

Gary, I think you're confused.

Here is simulated data with 28" of H2O (pressure ratio of 1.07). A flowbench at 28" of H2O is basically simulating 1lb (psi) of positive (boost) pressure. Flow the intake so it's 1psi drop compared to atmosphere. Blow through the exhaust port to produce 1psi of pressure compared to atmospheric.

speedtalkpressurefix.jpg

(click to see larger)
Note: port values are at the valve seat.

If David wanted to compare against a flowbench, he would have just produced data like that.

Looking at this, on the exhaust it sees a pressure of ~ +915"H2O and on the intake ~ -163"H20, at their respective peak/trough. Remember, at 7500rpm (like this graph), this is happening at 62.5x per second. This is what is calculated at the port, this is ignoring what the actual cylinder is in inH2O (which is technically what the flowbench would have to be - / +, or -203"H20 cylinder depression).

Note: the Y-axis is pressure ratio, or absolute pressure / atmospheric pressure. Hence, "1" would be atmospheric pressure.

I'm not sure on that EPI graph as the gradations aren't defined.

[hoffman900]

I should point out, if you look at the simulated pressure diagram I posted, there are ~30* crank degrees after IVO and before IVC where cylinder pressure is higher that port pressure at the seat.

The obvious answer is the cam is too long - yes it is to some degree, but it also needs some of that length for dynamic reasons to get to a higher valve lift.

[David Vizard]

I thought the graph would be a straight forward deal to read. I suspect many of you are reading what you expect to read not what the scales and labels actually say.
The scale up the left hand side is a multiple deal in as much as it is both Velocity and Pressure.
On the graph the red line labelled ‘cylinder pressure’ Vs crank angle is the only pressure curve.
The green line is the velocity through the area developed as the valve opens with maximum area occurring at 0.25 of the inner throat diameter.
The blue line is the port velocity and yes – if the valve area to port area is anything like right it will be faster than the velocity through the seat area.

DV

Bob - did you get my PM?

[MadBill]

OK David, but I have to say that the traces on this graph look exactly like the pressure curves displayed by Dynomation, with the red line being cylinder pressure, the green one representing exhaust pressure and blue referencing intake port pressure.

As such, I see the exhaust suction pulse centered on the overlap as one would wish, the third intake positive pulse peaking soon after IVC (ditto), and dropping below cylinder pressure prior to IVC, as expected at revs somewhat below that for which the cam events are specced...

[Erland Cox]

.
On the graph the red line labelled ‘cylinder pressure’ Vs crank angle is the only pressure curve.


DV

Cylinder pressure versus atmospheric or versus something else?

Erland

[digger]

It's always more useful to see exhaust pressure, cylinder pressure and inlet pressure (all referenced to atmospheric) on the same graph this way you can see pressure differentials and which way the flow is going.

At low to moderate rpm the piston depression won't be as much as at peak hp rpm but depression alone tells you little about mass flow and cylinder filling. I always like to look at cumulative cylinder fill to help identify where certain components offer advantages over other components with better or worse cylinder filling at different crank angles

[fabr]

Damn ,that was a LONG read. Wish I understood more than 1/2 of it. Just wondering if anything has been proven/proved wrong or just updated the last 4 years?

[steve cowan]

Damn ,that was a LONG read. Wish I understood more than 1/2 of it. Just wondering if anything has been proven/proved wrong or just updated the last 4 years?

I cant prove/disprove anything
I ran 50 deg on a small headed 383 last year mild lobe Howard's shelf cam ,dozens of passes, street miles etc.
Pulled engine to upgrade to a dart block.
Seats look great,intake seat looked untouched, exhaust not beat up at all just carbon ring.
My opinion is people have to try different things for themselves, my machine shop would not do the valve job I wanted,I bought stones,valve facing machine etc and just done the work myself.