Ferocity02

iTrader: (60)

Well after reading the sticky in this forum, it got me thinking about the surface texture of heads in the intake and exhaust ports. I am interested in this because I am going to be buying some heads soon for my 427 project. I am looking at the AFR 225's, Patriot Stage III LS6, or the LS7 heads. I have seen pics of all of these and the surface texture varies. The Patriots have a very ridgy texture, while the AFR's are really smooth. There are some pics below of the pics I found. The pics of PRC's are supposed to be hand finished, but look like crap IMO. I can only assume that the smoother the better, right? So why do some heads come with a ridgy texture? Cost efficient? Do the ridges provide some sort of aerodynamic benefit, like swirling the air before it enters the cylinder? I am thinking that pretty much any head I get, except for AFR, I am going to want to go through with the sand paper to smooth and polish the intake and exhaust ports, then polish them up a little bit.

Right now I am leaning towards the LS7 heads. They only cost a little more bare than the Patriots do bare. Plus they are supposed to flow crazy numbers.

Any thoughts/ideas/expiriences are welcome. I would like to learn more about head design.

LS7 Heads:
http://12.203.3.3:6580/LS7Stuff/IMG_3701.JPG

PRC Heads:
http://members.***.net/ss20493/videos/prcheads.jpg
http://members.***.net/ss20493/videos/prcheads4.jpg

Patriot Heads:
http://i3.photobucket.com/albums/y98...o/100_0739.jpg
http://i3.photobucket.com/albums/y98...o/100_0757.jpg
http://ourworld.cs.com/ls1info/Patri...s/DSC00034.JPG
http://ourworld.cs.com/ls1info/Patri...s/DSC00027.JPG
http://ourworld.cs.com/ls1info/Patri...s/DSC00026.JPG

Unknown Heads:
http://img.photobucket.com/albums/v2...n/100_2115.jpg

Lasershop

iTrader: (2)

It is pretty much a cost issue, but can be the discretion of whoever is doing the programming. CNC tool paths are made up of "steps". Ideally, you would have a rough cut and then multiple finish operations with a CNC mill. On a production basis time is everything so many vendors are doing the entire operation in just one pass. That leads to tool chattering from removing a lot of material at one time. The depth steps (the lines you see in the ports) indicates how many and the spacing of the pecks. A step of what seems to be around .1" is a lot courser that steps of .005", but is 20 times faster to do. A super glass smooth CNC porting job is going to take all day, and cost a whole lot more money. The hand finishing option is still very much alive and well but most shops that offer "port polishing" really is an 80 or 100 grit finish and they all say it is not beneficial. But then...... I don't understand the concept of "Rat Rods" either. I understand the atomization and fuel pooling issue with carburated engines as far as ports being too smooth but on the LS1 the injector fires at the back side of the intake valve so I fail to see the benefit of "rough" ports leading to the bowl. Production porting is one thing, custom porting is another.

Worked every day for two months on these. Shop who set them up said they are pretty but to rough them up. I stuck with pretty.........

TAQuickness

iTrader: (28)

Excellent thread Ferocity02 - I have been wondering the same as I try to decide whether or not I want to upgrade my heads. I would imagine a rougher texture would aid in the "mixing", but I'm no head expert either.

Nine Ball

iTrader: (38)

This is a good question to discuss Its based on Fluid Dynamics.

The effect of surface texture on flow is derived from two-dimensional anaylsis of fluid flows across a surface. What we desire to do is reduce the height of the boundary layer of flow across the surface, in order to maximize a laminar flow quality. There are two types of flow to consider, laminar (smooth) and turbulent. We also need to consider two different flow velocities when speaking about engines, subsonic and supersonic.

Intake flow velocity is subsonic, which is slower than supersonic of course. It has been proven by testing and mathematics that subsonic flows generally form a smoother (less height displacement) boundary layer on a slightly textured surface, compared to a smooth surface.

For example, take a golf ball. What are those dimples on the surface for? They are on the ball to help the flow "hug" the surface of the ball, which greatly reduces the boundary layer of flow across the surface. This creates less turbulence across the surface. Without the dimples, the golf ball would only fly about 2/3 of the distance it normally does. Thats why you never see smooth golf *****!

Intake ports benefit from a slightly textured surface. Polishing them to a mirror finish has shown no benefit. Some head porters glass bead the surface, some of them leave the sanding marks, some of them leave the CNC tool path marks. Even a nice smooth cast finish will work.

Exhaust flow is supersonic, and relies less on the surface texture. With supersonic speeds, there are slightly better gains shown with a high polished flow surface. Supersonic flow is less dependent on boundary layer flow, its more dependent on moving more quantity out, at high speeds. A smoother surface will help reduce restrictions at this higher flow velocity.

If you are interested in the math behind Boundary Layers and Laminar/Turbulent flows, here are some links I found:
http://wings.avkids.com/Book/Flight/...d/move-01.html
http://www.allstar.fiu.edu/aero/Wing34.htm
http://www.see.ed.ac.uk/~johnc/teach...eparation.html

TAQuickness

iTrader: (28)

didn't have to lurk long. thanks for the info Tony

ninobrn99

iTrader: (8)

omg!! those things look amazing!!

Nine Ball

iTrader: (38)

Polished combustion chambers are typically a good idea, since they provide less chance of pre-ignition from happening. On a smooth combustion chamber like those, there are less hot spots likely to form, which cause pre-ignition. The exhaust ports on that head would be great, but I'd rough up the intake ports slightly.

Lasershop

iTrader: (2)

I hear what your saying, heard it all before, but WHY do they benefit? Specifically fuel injection where it is just "air" traveling through the ports. Haven't seen too many bullets or planes with dimples all over. Not just trying to argue..... really would like to know.

Lasershop

iTrader: (2)

Re read your post
"Intake flow velocity is subsonic, which is slower than supersonic of course. It has been proven by testing and mathematics that subsonic flows generally form a smoother (less height displacement) boundary layer on a slightly textured surface, compared to a smooth surface."
Pretty much does explain it. Going to research this.
Thanks, RonO

Nine Ball

iTrader: (38)

Bullets travel supersonic. Smooth surfaces are better in that case.

Airplanes use the shape of their wings to create lift, they aren't as concerned with surface texture. They are also streamlined by design, and do not create much drag. Same with cars, who would buy a dimpled body car? Some item designs are driven by aesthetics, some by function over form.

Do some research on head porters, maybe call a few of them and ask about surface texture. I can pretty much guarantee none of them will have mirror polished intake ports. Some of them might not know why its bad (haha), but I'll bet they tell you to leave the intakes slightly textured.

Its just about laminar flow across the surface. Slightly textured surface causes the first layer of flow (boundary layer) to hug the surface. This reduces flow friction at subsonic speeds, and allows the flow layers above the boundary layer to 'slip' more easily and reduce turbulence. Turbulence at subsonic speeds causes flow velocity to suffer.

Tony

Nine Ball

iTrader: (38)

I found a good link, that describes exactly what you just asked:
http://www.aerospaceweb.org/question...cs/q0215.shtml

Lasershop

iTrader: (2)

Had chinese food the other day. My fortune cookie read "A wise man will learn more from a fool than a fool will learn from a wise man". Not sure where I fit in there. You are right about many porters. They do but dont know why and I have a bad habit of dismissing some old school statements without the facts. As far as the thread goes, would you agree that the quality and smoothness of available ports can be dependent on cost or just plain sloppy work?

ninobrn99

iTrader: (8)

thats quite a bit to take in at once maybe i need to stay in the internal forum for now

Lasershop

iTrader: (2)

You should not have replied with that link. Now I have a new question. I read it and it concerns it flowing around objects. Specifically a sphere. Ports are a volume of air traveling within, and not around except for the guide boss. That seems completely different even as far as the being the opposite to me.

Nine Ball

iTrader: (38)

No, because I've seen some excellent head porters take a perfectly nice looking and polished port and then hit them with the glass bead blaster to texture the intake ports. I've also seen some use Scotchbrite pad looking drill bits, and some just use a med grade sanding roll. I've also seen their flow bench tests before/after, and the slightly textured ones put out better flow numbers. Its just basic fluid dynamics, backed up by calculations.

Now, some head porters just do sloppy work, period.

I'm an Engineer, so just like yourself, I asked alot of questions too! I also enjoy finding proof and calculations of why things work like they do.

BigPurp

Ahh but thats where your a little off base here, the intake port on any efi motor is still wet flowing. The manifold may be dry for 99% of it (up to the injector port) but irregardless of where the injector points it will still be an atomized fuel/air mixture (that is the idea right). The injector isn't spraying a stream right into the intake valve, it's a misting spray that fills the intake port, thus wet flow. You would benefit from roughing up those intake ports as stated. They sure are purrdy tho.

Nine Ball

iTrader: (38)

Yes, it can be confusing. You have to imagine just a portion of the surface of that golf ball. Its all about fluid flow over a surface (not an object). Fluid flow over a surface follows the same rules no matter what, whether that is over a golf ball or inside of a pipe. The goals are the same, to reduce the boundary layer along the surface, and to reduce turbulence.

Fun, isn't it?

Lasershop

iTrader: (2)

I know what a pain in the *** I can be in a debate.... but I am learning from from you ( Mr. 9 ball) and appreciate your patience.

Nine Ball

iTrader: (38)

Here is some good reading about how flow goes thru a pipe/intake. They mention boundary layer, and how velocity is highest at the center of the pipe. Boundary layer causes flow friction, and textured surfaces reduce the size of the boundary layer, which increases the velocity at the center of the pipe. Another thing mentioned is smooth curves and piping for intakes and exhaust. Thats another principle, I'm sure most people know that more bends means more restriction due to changes in flow path causing turbulence. Thats why we use mandrel bends and slight angles in those bends, if possible. But, I suppose we are discussing surface texture within those intake tracts, so I'll keep on the subject.

http://www.bankspower.com/tech_howairflows.cfm

Lasershop

iTrader: (2)

My wife suggested that she was a little frisky......... but I told her I was going to read an article on how air is a fluid. A fluid defined as having particles that easily move and change their relative position without a separation of the mass and that easily yield to pressure: ......... and now was not a good time.......
The Vette' needs my attention right now.