I just came to think about it.. If it makes a golf ball go faster, straighter, and longer, why wouldn't it do wonders for the flow rate of intake ports?
I haven't seen it mentioned anywhere.. Has anyone ever tried to make a zillion golfball-like dimples in a port and (flow) tested it? If not, is there anyone that would be willing to give it a try?

 

Expert engine builders flow check heads while spraying blue machinist die into the air stream. This blue die then collects in certain areas where fuel is pulled out of the atomized mix (this is bad). They (machinists) will then put little divots into the chamber or port in this area and a little bit in front. The divots work kind of like the golf ball thing you mentioned. The divots help keep the fuel atomized...

You have to remember though that a golf ball is the object flying through the air after being hit (really hard). A port and chamber has air flowing through it as a result of a vaccum. So these two situations are somewhat similar yet very different.

 

I've seen that sort of idea, can't remember where I saw it though. Also, "CNC ported heads" have cut marks left in them, probably for the same reason.

But I must admit, I am getting really tired of hearing about people talking about the whole golf ball analogy. That's the only comparison that really holds any merit, and it is based on a different situation. With my vague grasp of fluid mechanics, I think a smooth bore would work best. But I would really like to see a more concrete test.

 

I looked this up on wikipedia once and it discusses they have done flow benches to test the theory but doesnt seem like anything to get overly excited about.

Cylinder head porting - Wikipedia, the free encyclopedia

 

I'm sorry for bringing up an old concept without doing a thorough search on the topic first, but it seems such a good idea to introduce "virtual" ball bearings for the airstream.. Someone in this world must've been crazy enough to try it out for real on a head and presented the result..
While it may be claimed that there's a difference between a ball flying through air and air flowing through a tube, I think the only difference is that the ball has only a (small) specific packet of energy by which to keep moving whereas in an engine you have "unlimited" energy sucking air with greater pressure differences involved so that the effect any dimples could've had may become small. I'd still want to know if this has actually been tested with dimples or something similar, not just with a rough texture. And how rough is rough? The articles states that the roughness must protrude into the actual airflow to have any effect.
The picture of the velocity profile in the mentioned Wikipedia article shows that the air flow is zero at the walls. I believe the dimples would make the velocity profile more square. The only question then is how much is actually to be gained by this in real life. A fifth of an inch, or only a 20th of an inch? I also believe that the turbulent boundary layer introduced by dimples or such could improve the behaviour of a small short turn radius, as shown in this article: Golf Ball's Interaction with Air.

 

If you read the wikipedia article it mentions even with dimples the air velocity at the walls is zero so the only gain would be for fuel atomization.

 

Well, yes, I read the article, and it mentions only the small differences between a rough textured finish, a smooth to the touch finish, and a mirror like finish.. Then it says:
"In order for surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center. Only a very rough surface does this."
How rough is a non-smoothed CNC-finish, which I think is said to be somewhat beneficial?
I'm sorry but I don't find where it says anything about zero wall velocity even with dimples, and I still would like to see some actual evidence about what dimples or such will do to the airstream apart for the fuel atomization bit..

 

Yes but the difference between a rough and polished surface when compared in cfm is less than a 1% difference. The benefit is mainly for fuel atomization. So what makes you think by putting dimples that this would be a major advantage. The dimples in a golf ball are basically for controlling spin which seems like a completely different function all together.

 

All the theory in the world is great and can be talked about forever. Here's an idea. Go to your local junk yard, get a head and try it.

 

Heh, I'm in fluid mechanics right now. The thing about a golf ball is that it messes with the normal flow of air over it. Since in a cylinder head, you want the air to go through as fast and undisturbed as possible, this wouldn't be a good idea. Are you familiar with what a Reynolds number is? Or relative roughness? Minor losses expressed in a change in height (p = rho * g * h) and so forth. Since a bunch of dimples would just make the ports rough, I'd say bad idea.

 

AHA, you're back!

I got a D+ in fluid mechanics, my lowest mark ever. Well, tied with AMAT317 (the widow maker), differential equations. cough, anyway...

However, I have enough knowledge to make some members on this board shudder from the sheer nerdy-ness, but I like to have someone else here to throw out nerdy terms with

Reynolds # eh? That's where it goes laminar -> transitional flow around 1800, then to fully turbulent in the low 2000's? Something along those lines eh?

Main thing I think of - is how it screws with the boundary layer. The flow in a cylinder head, I imagine would be hardcore turbulent, if if was linear, you'd have fuel puddling like crazy. Turbulent flow is great for mixing. Anyway, you no longer have a reasonable velocity profile, it'd be all wacky!

Here's some nifty reading that I just found, to refresh my memory;
Viscosity and Boundary Layers
Boundary Layer <---nasa.gov, cooool!

Food for thought - A golf ball has dimples, not necessarily to control spin (I don't golf, so I might be wrong), but to help it fly further and straighter. Now, that helps the ball. What about the air around it? In the cylinder head, you don't give a %*&^( about the head, you want the AIR to be moving quickly. The only reason I can think of for the dimples is to upset the boundary layer, and to try to keep fuel from puddling. That seems to be a viable consensus, however it is bad for flow, but that's minimal.
Which is perfectly stealing the words from shaggy's mouth:
So, if we can all agree on that, then we can all just move along As for dimples though, that should be the same effect as the "rough" port. Rough being very relative, rough meaning 80 grit sandpaper finish. A "dimple" is GIGANTIC compared to what the sandpaper finish would be, and would be overkill for the purpose at hand (prevent fuel dropout).

....gasp!

 

Ah, I never left. I just lurk more now than I used to. :P

Yeah, we use 2300 as the transition for the renoylds number. Interesting.

The reason the dimples on the golf ball make it fly farther and straighter is because they induce backspin on the ball. But yeah, since we're talking about relative roughness and other minor losses, the keyword being minor, I'd fully agree with that 1% rule. Definately nothing you'll ever feel in the butt dyno. Now maybe if this were being done on my 240 and I had other supporting mods, where I dont have to worry so much about atomization because of the turbo and such, then I'd want to go smoother than rougher. But even so, there are other things more demanding of my attention than the precise roughness of my head ports.

 

Yea, the dismal lack of displacement, haha zing!

 

hahaha. Yeah, that still pisses me off. Check this out, though. VERY tempting!

Since it's aluminum and my KA24DE is iron, it'd probably weigh less, too. And since according to the sticker on the door sill the car only weighs 2660 lbs as it is.....

 

Holy COW! Now that's something i'd respect! Like one of those old POS datsuns with a LS1 (seen one online once, with a blower, flat out crazy...)

What tranny though?

That would be a fitting graduation present to yourself Mine is going to be a 240V stick welder, 240V vertical air compressor, and probably a big gear-head milling machine. Then again, maybe i'll work at a place that lets me use theirs

 

Yeah, I'm pretty much ALL OVER that. And yeah, my grad present is gonna be an engine. As for the trans, a t56 w/ custom driveshaft.

I'm also hoping to get to work somewhere like that. Heh.

 

That's it!
I'm getting some concrete heads to try .
No more problems with mirror smooth intake ports...

 

hey, good idea It'll be already "ceramic" coated too Low thermal conductivity... Cracks are easy to fill in too...

 

Not great for vibration though.

 

~~Rock Steady~~
*humming the tune*
I do expect some difficulty tapping the holes in them though...

 

Or rather, never mind..