Low Angle Port

[Desmoguzzi]

After have read many documents and books i've got that One of the weak point of low Angle ports Is the short side radius. So almost all the head porters suggest tò rise the floor in order to improve the SSR and enlarge the port on the sides to achieve the correct cross section area.

In very few cases i read about different and totally opposite approach: make the intake runner straight and use only half of the curtain area. In this case the benefit Is to have an High coefficiente of discharge because the air is free tò enter into the Chamber (even if using only half curtain) without finding on the Path the obstacle of the valve. In the attachment you can see an example of this kind of Port. Looking at some racing engines It seems to me that this approach Is often used .

Some of you have ever tried to shape a low angle Port in this way? Did you find any real benefit? Thanks in advance.

[Tom68]

After have read many documents and books i've got that One of the weak point of low Angle ports Is the short side radius. So almost all the head porters suggest tò rise the floor in order to improve the SSR and enlarge the port on the sides to achieve the correct cross section area.

In very few cases i read about different and totally opposite approach: make the intake runner straight and use only half of the curtain area. In this case the benefit Is to have an High coefficiente of discharge because the air is free tò enter into the Chamber (even if using only half curtain) without finding on the Path the obstacle of the valve. In the attachment you can see an example of this kind of Port. Looking at some racing engines It seems to me that this approach Is often used .

Some of you have ever tried to shape a low angle Port in this way? Did you find any real benefit? Thanks in advance.

That's how some people try to get flat heads to flow. Using half the valve is probably OK if you have massive valves in a small engine that doesn't need to make power over 4000 rpm.

[mag2555]

I can’t see how you would take much advantage of Ram tuning and shock wave tuning in a engine when your limited to a lift of 50% of only .25D.

In a case like this port shape and SSR height is near meaningless other then what the valve angles themselves form.

[dannobee]

Here's how Honda did it about 15 years ago. Modern designs are even straighter.

And here's another head.

https://www.f1technical.net/forum/viewtopic.php?t=15385

[PackardV8]

FWIW, some flathead folk who have the cred say don't give away the back side of the valve or flow out the back and over the top.

use only half of the curtain area. In this case the benefit Is to have an High coefficiente of discharge

My guess is velocity/COD runs out of steam very quickly when using only half the valve curtain area.

[Walter R. Malik]

In that drawing, it looks to me as if the floor of the port was actually lowered in order to try to create a longer short side radius; though not very much.

[Tom68]

In that drawing, it looks to me as if the floor of the port was actually lowered in order to try to create some short side radius; though not very much.

I think that's just deck thickness to hold the gasket in place.

[Desmoguzzi]

Just to report a real example of this kind of Port .

port-matching.jpg

[Desmoguzzi]

Here's how Honda did it about 15 years ago. Modern designs are even straighter.

And here's another head.

https://www.f1technical.net/forum/viewtopic.php?t=15385

That's true but F1 engine should not look for Tumble because the strike Is too short.

[Tom68]

That's true but F1 engine should not look for Tumble because the strike Is too short.

That inlet runner port matching pic you posted looks even worse than this runner, seems packaging and emissions might be more of a priority than top end horsepower.

Nearly as bad.jpg

[LotusElise]

After have read many documents and books i've got that One of the weak point of low Angle ports Is the short side radius. So almost all the head porters suggest tò rise the floor in order to improve the SSR and enlarge the port on the sides to achieve the correct cross section area.

Rising the floor is one way, the other way is to follow the natural evolutions of bend flows. If you widen the width of the port and compensate with an even lower Short turn radius then you have less shear tension in the flow. I have tested this, it works quite well. But this is also old stuff and well known since the 70'ies.

[Desmoguzzi]

After have read many documents and books i've got that One of the weak point of low Angle ports Is the short side radius. So almost all the head porters suggest tò rise the floor in order to improve the SSR and enlarge the port on the sides to achieve the correct cross section area.

Rising the floor is one way, the other way is to follow the natural evolutions of bend flows. If you widen the width of the port and compensate with an even lower Short turn radius then you have less shear tension in the flow. I have tested this, it works quite well. But this is also old stuff and well known since the 70'ies.

The attachment Is a pics taken from a Divad Vizard book. Even if the SSR Is very Wide the air want go straight and naturally It Is used mostly only half of the curtain.

IMG_20221004_095142.jpg

[LotusElise]

If you seat between the air molecules at for example 100 m/s and your body is having some weight, it is easy to understand you won't follow the bend immediately and only with some friction at your neighbour molecules.

The approach to "squeeze" the port like a garden showering hose with two fingers (shape-wise) will increase the flow-loaded area and reduce the unused area. Just increasing the bottom is not the same regarding efficiency, it just reduces the unused area, but doesn't increase the used, as the valve is still circle shaped.

[Erland Cox]

On a 4 valve with big enough valve area a straight port is OK.
The more the flow is over one side of the valve the more tumble is generated.
But as rpm goes up this requires shorter stroke, bigger bore and larger valves.
And this gives combustion problems so you have to go to a port that flows more around the whole valve.
It really depends on the configuration.
On a flat head I go with tis type of port and flow straight into the cylinder.
On a 2 valve engine it is nice with a line of sight port and a high SSR but all heads aren't SB2:s.
If the short side is low the air is not going to turn well anyhow so pulling the throat on the port side closer to the seat
helps more air get around the valve.

Erland

[Erland Cox]

Modern direct injection 4 valves even have a ramp that directs the air over the valve for more tumble.
Porting for more low around the short side does not always help as a lot of tumble is needed.

Erland