Ported heads

[SilverPig]

Aaaalrighty then! I've already discussed this briefly with JHU, but I thought you guys would have a say in this as well: On ported heads, the valve guides are often exposed, totally unlike original heads. In my mind, this would create a much less smoother path for the air/fuel mixture to pass by...or am I mistaken?

[Andi/DFL]

from a fluid dynamics point of view I would say that it is not that bad. being round, they will cause small swirls in the mixture behind the valve guides, but that doesn't have to be a disadvantage. Could be that it even helps to build a more homogenic mixture. They also shouldn't slow the mixture down a lot, just directly behind the valve guides.
But that's just theoretical knowledge...

[SilverPig]

Exactly! Those swirls would be what causes drag. Maybe the mixture gets more evenly distributed, but it should also slow it down...according to this theory.

[Jon]

I dont know, but I think there is a reason for a water drop to take on the shape it has when free faling. Might not have anything to do with anything.

[Andi/DFL]

well, if you put a sphere in a flow area, you have lower flow speed directly behind the sphere. the size of the low-speed area (translated from german: "dead-water-area") depends on the flow speed and the pressure specs (size of inlet/outleft of the port). Usually this area is not very big, but the point where the flow tears off of the sphere (= valve guide) moves forward on the sphere when the flow speed increases, thus the low-speed-area gets bigger.

If I'd have some specs of the flow area (speed, inlet/outlet diameter, valve guide diameter, angle of valve guide in the flow area) I could do a fluid simulation (static = constant flow speed), and compare it to one without the valve guide. But maybe that goes a little too far? :-)

[BeetleBug]

Interesting topic!

Recently a guy told me that the area around valve guides is by far the most important area to consider after the valve seat. He got me thinking and after a while thinking about the topic I started looking at some pictures. I soon realised that all the heads I have seen that is really fast have shaped edges around the valve guides. Look at the pictures, these heads is used on one of the fastest cars in Europe (natural aspirated that is);

Best rgs
BeetleBug

[Andi/DFL]

that are nice pictures and the area around the valve guides looks very nice. Could be, that, if you add the same shape behind the valve guide, it would be even better. This could prevent the flow to tear off of the "walls" of the valve guide (which causes the swirls).

[BeetleBug]

Hard to see but they are shaped behind the guides as well - not so agressive compared to above. I find the finish in the port quite interesting as well - not to mentioned the size of the port but that`s a other story.

[Andi/DFL]

yes, size DOES matter :-)

[Jon]

And speed...      Here in "Feet pr minute"....  and 300 is the magic number I seem to remember

[bullitt]

mmmmh could be interesting to forge a new type of wing shaped (reverse drop) valve giude

unfortunately we lost wing enthusiast colin chapman some years ago.....

[TiDi]

Another theory is that you can have dimpled valve giude...

Dimpled balls fly farther than non dimpled balls due to the combination of two effects:

Firstly, the dimples delay separation of the boundary layer from the ball. Early separation, as seen on a smooth sphere, causes significant wake turbulence, the principal cause of drag. The separation delay caused by the dimples therefore reduces this wake turbulence, and hence the drag.

Secondly, backspin generates lift by deforming the airflow around the ball, in a similar manner to an airplane wing. Backspin is imparted in almost every shot due to the golf club's loft (i.e. angle between the clubface and a vertical plane). A backspinning ball experiences an upward lift force which makes it fly higher and longer than a ball without spin would. Sidespin occurs when the clubface is not aligned perpendicularly to the direction of swing, leading to a lift force that makes the ball curve to one side or the other. Unfortunately the dimples magnify this effect as well as the more desirable upward lift derived from pure backspin. (Some dimple designs are claimed to reduce sidespin effects.)

In order to keep the aerodynamics optimal, the ball needs to be clean. Golfers can wash their balls manually, but there are also mechanical ball washers available.

Bye TD

[quickkafer]

Did you hear about the drunk guy that broke his leg playing golf?

He fell off of the ball washer!

This is a very interesting thread to me.  I've been gathering lots of information from some the well known head porters in the industry and a fellow enthusiast emailed me a copy of an article that appeared in Grassroots Motorsports magazine.  There is soooo much that goes into getting a good set of heads, that it makes my head hurt!

Air speed, port volume, CR, cam selection, etc. are all vital to getting the gains that we want.  I've got a set of professionally ported 044's from Heads Up performance for my 2 liter, but they're too big to use as models for my 1776 project.

But one question I still have is, with the added flow, how much does the RPM range for power change?  For instance if with non-ported heads, if I was generating peak power at 3500 RPM, will a ported head (nothing else changes: carbs, valves, etc) move the power band up or down?

Scott Faivre

[Jordy/DVK]

But one question I still have is, with the added flow, how much does the RPM range for power change?  For instance if with non-ported heads, if I was generating peak power at 3500 RPM, will a ported head (nothing else changes: carbs, valves, etc) move the power band up or down?

 The easier the flow, the more air can get into your combustion chamber. Filling the combustion chamber is not critical at low RPMs, because you don't have a huge airflow.
 It is critical at high RPM's, because the air needs to be drawn in in a much shorter period of time. Better flow = More mixture (at high RPM) = more pressure = more Nm at that rpm...
 more Nm x rev = more kW = more HP (at the higher revs)

 It'll move your powerband up...

 Here's an interesting introduction into head porting principles:
 http://www.popularhotrodding.com/tech/0610phr_cylinder_head_porting/index.html


 Btw has any of you ever thought about the right length of their intakes/velocity stacks to make use of "Ram Pressure Tuning"?

[quickkafer]

 Here's an interesting introduction into head porting principles:
 http://www.popularhotrodding.com/tech/0610phr_cylinder_head_porting/index.html

That's a very similar article to the one in Grassroots Motorsports Magazine.  The author (Davis Vizard) and all the diagrams are all the same!  Too cool!

I hadn't seen that on popular hot rodding's site!  Thank you for sharing!!!

Scott Faivre

[Airspeed]

Also think about the strength of the guide! The more the guide has been embedded and supported into the head, the more stable the seating is and the better and longer the cylinder holds its compression. It (the ridge) also gives more contact area for heat flow into the head where it can dissipate through the fins (if you have any  )

[Sander/DVK]

Also think about the strength of the guide! The more the guide has been embedded and supported into the head, the more stable the seating is and the better and longer the cylinder holds its compression. It (the ridge) also gives more contact area for heat flow into the head where it can dissipate through the fins (if you have any  )

Walter??
What the heck are you doing here

[Diederick/DVK]

yeah! german look attack!!!!!!!!!!!!
they're invading!!

and don't seek cover! instead let the IDAs growl 

[quickkafer]

Interesting topic!

Recently a guy told me that the area around valve guides is by far the most important area to consider after the valve seat. He got me thinking and after a while thinking about the topic I started looking at some pictures. I soon realised that all the heads I have seen that is really fast have shaped edges around the valve guides. Look at the pictures, these heads is used on one of the fastest cars in Europe (natural aspirated that is);

Best rgs
BeetleBug

BeetleBug,
    Do you know what castings those heads were based upon?  Stock heads? 044's? Street Eliminators?
Thanks!
Scott Faivre

[BeetleBug]

Interesting topic!

Recently a guy told me that the area around valve guides is by far the most important area to consider after the valve seat. He got me thinking and after a while thinking about the topic I started looking at some pictures. I soon realised that all the heads I have seen that is really fast have shaped edges around the valve guides. Look at the pictures, these heads is used on one of the fastest cars in Europe (natural aspirated that is);

Best rgs
BeetleBug

BeetleBug,
    Do you know what castings those heads were based upon?  Stock heads? 044's? Street Eliminators?
Thanks!
Scott Faivre

Hi Scott,

Those are old SuperFlo heads. Further uo in this thread there is some talk about golf balls and their dimples. The intake and the manifold on the heads I`m talking about have small dimples in them - almost like a golf ball. Again very hard to show on a picture.......

BB

[Alan Uyeno]

And speed...      Here in "Feet pr minute"....  and 300 is the magic number I seem to remember

In a vw casting anything over 350 fps will cause turbulence but in a straighter port like a Comp Eliminator this wont be the case.