CFD/CAD/Thread

[SpeierRacingHeads]

So for a novice or someone looking on, if you had to pick one simulation that is most important, which would it be?

Pressure?

[ClassAct]

To save time I went ahead and made some changes.

The changes that made the most difference are:
1. Reshaping the pinch area, both sides, top and floor.
2. Reshape the manifold to make the top and floor tangent to the port.
Increase the radius of the turn at the end
3. Reshape the long side of the turn to reduce volume to conform to volume rule.
4. Reshape the guide boss to fill volume and reduce drag

This reduced the cylinder vacuum considerably.
The challenge is that this requires greater pushrod offset, probably about 0.250"
So we have to make a decision of whether to use a rocker with more offset or try to make a lower floor substitute.
Doubtful that the lower floor will work as well.

To make this design work, a slightly different design is needed for left/right inner/outer are required (4 different ports).
A manifold with perpendicular runners would make that unnecessary and probably improve performance.

JT files in next post.

Side view
side.png

Top view
top_pushrod soften turn.png

Reflections show smoothness
reflection 1.png
reflection 2.png

Velocity section
velocity_section_long.png

Vorticity
vorticity_section_long.png

Pressure Vacuum reduced from 5.297psi to 4.832psi
pressure.png

Just as an FYI, there is a whole army of head porters out there who think the pushrod pinch is of little importance. Your testing shows it is.

That right there will hurt some feelings.

Thanks to you and Chad for doing this and putting it out there. It’s much appreciated.

[SchmidtMotorWorks]

Just as an FYI, there is a whole army of head porters out there who think the pushrod pinch is of little importance. Your testing shows it is.

That right there will hurt some feelings.

Thanks to you and Chad for doing this and putting it out there. It’s much appreciated.

Hopefully we are all seekers rather than believers, that way we are open to discoveries.

[SchmidtMotorWorks]

Here is a list of section area and perimeter measurements

section areas.png

[SpeierRacingHeads]

Here is a list of section area and perimeter measurements

section areas.png

And this would need around a .250 offset?

Can you do a cross section of the original port?

[In-Tech]

Hiya guys,
Just following along, awesome thread. Chad, does the class require a guide plate type rocker? If not, shaft rockers and no pushrod pinch is great, then put material back to maintain the CC's where the CFD can take advantage of a better shape

edit, speaking to the choir

[SchmidtMotorWorks]

Here are some comparisons between the scanned and CAD geometry

Replacing images, hold on

[fordified]

You may want to put a very small wing on the floor to see if it’ll reduce vorticity around the valve. You may have to move it around the floor relative to the valve. Try making it perpendicular to the valve.

It should be placed in such a way that it doesn’t affect the short turn or the bore center flow path. It should end at the apex but you’re going to have to play with it. It’s going to be time consuming to get it right if it has any positive effect at all.

Keep it thin but not razor thin. The top should have a radius however small. It doesn’t have to be symmetrical side to side. It should slope front to back. It may need to be higher than you expect at the end but floor height at the beginning. You should offset it favoring the bore wall.

[SchmidtMotorWorks]

And this would need around a .250 offset?

Can you do a cross section of the original port?

The scanned port is 1.668^2" measured at the brown CSYS perpendicular to flow rather than measured on the angled face.

The new design is about 0.20 more open toward the pushrod.
The opposite side is pulled in some.

Since you already have a 0.250 offset, you would need about 0.450 total offset.

Your pushrods are fairly straight now, maybe you could live with another 0.200 offset.

[SchmidtMotorWorks]

You may want to put a very small wing on the floor to see if it’ll reduce vorticity around the valve. You may have to move it around the floor relative to the valve. Try making it perpendicular to the valve.

It should be placed in such a way that it doesn’t affect the short turn or the bore center flow path. It should end at the apex but you’re going to have to play with it. It’s going to be time consuming to get it right if it has any positive effect at all.

Keep it thin but not razor thin. The top should have a radius however small. It doesn’t have to be symmetrical side to side. It should slope front to back. It may need to be higher than you expect at the end but floor height at the beginning. You should offset it favoring the bore wall.

I did about 70 experiments last night including those.

[fordified]

It shows. The gradients look great. Now flow it.

[SchmidtMotorWorks]

The images keep duplicating

scan_vs_cad4.png

scan_vs_cad6.png

[SchmidtMotorWorks]

It shows. The gradients look great. Now flow it.

That is what the cylinder pressure tells you.
From memory the vacuum is about 0.4 psi less out of about 5psi.
It is more meaningful to an engine simulation because the chamber and cylinder flow follows the piston and recirculates as it does in an engine rather than flow down an endless cylinder.

[SchmidtMotorWorks]

So for a novice or someone looking on, if you had to pick one simulation that is most important, which would it be?

Pressure?

If I am trying to make a lot of progress fast, I look at velocity 90% an pressure and vorticity 5%.
That said, pressure and velocity are inverse of each other, if was possible to flip the color legend, they would probably look very similar.

I look for areas on the surface that are red-ish, and enlarge the area there, and look for areas that are not as red, and remove material there.
The key is making one small change at a time.
If I do that as fast as possible, make a small change, run the sim, that can be a 5-10 minute cycle.
The is about 5-10 per hour (while watching YouTube). In 6 hours, I can do about 40 or more.

The arch of the floor is a little different, when you get to the point of diminishing returns, very small changes make big differences to downstream flow.

[SchmidtMotorWorks]

All this work was done without consideration for the chamber and valve job. The throat of the seat needs some work but the is no mystery there.

I don't know if there is any opportunity here given the as cast chamber is so big and it can't be welded.

That said, there is sometimes more to be gained in a chamber than a port, so if we could get a good scan or CAD of an as cast chamber, we can explore the possibilities.