Why not?

My brother used to be a mechanic for a rally team and they spent a fortune on porting and polishing the ports on the old mini's to get extra HP out of them. All full race engines at that time used two twin choke 45 Webber carbs with one choke cut of of each (seems it was more efficient than using both the chokes on one) and had the inlet manifolds and ports highly polished.

 

The reason is, air likes to stick to polished surfaces. The best way I can describe it, is, air smears and sticks along the surface. This is not good for max air-flow. It's a boundary layer effect.

 

EXACTLY !! Its my understanding that the FUEL sticks to the smooth surfaces ( smooth as in like pollished chrome ) too.

theres more adhesion (sp?) to a smooth surface than a rough surface.

The real question I have is how smooth/rough/polished is the surface supposed to be? Obvoiusly not as rought as it comes stock but should it be as smooth as 600 wet dry sandpaper or what? Do you know what I mean? Everybodys idea of "rough" is going to be different.

Heres another one.... do you grind/sand the metal inline with the direction of the flow or is it ok to go against?

Hmmmm ......

 

If you want my opinion on this, what I consider real rough is fine. How rough is real rough? I've seen pro ported heads and they leave the tool grinder marks in them, so I do the same. I polish the exhaust and combustion chamber to a mirror finish, but I just leave the carbon burr marks in the intake tract.
Prozack, you also have to remember that you not only have to worry about fuel drop out, (as you have talked about) you also have to worry about air flow. A rough surface will out flow a smooth one. (Think, golf ball and shark) Sand a golf ball smooth and see how far it goes. The guy that thought of putting dimples on a ball was a genius!!!!!
On the subject, a good buddy of mine works for a BIG exhaust company. They have flow tested and dyno'ed engines that have had their intakes extrude honed. The results were very dissapointing. He told me that I would be far better off grinding the intake with a burr and don't waste the $$$$'s on the extrude hone deal. That was their research anyway.

 

What's up Doc??? lol The local engine builder here (mostly round track cars) also says extrude honing sucks. You can't control the reshaping it does, like valve guides/pockets etc.

He also says the best texture for aluminum on intake side is glass bead blasting, of course mirror polished on exhaust.

Another guy who mostly builds Banshees also says that the fuel will adhere to a polished intake because of surface tension. And says to think of the airflow like boat racing, they will go faster on choppier water than smooth, because there is less contact and drag.

I think you want it smooth (no bumps or lumps) but want it "fuzzy" feeling.

 

Great, great analogy DCryder!!!!!!! Sounds like this guy would be the person to build my Banshee if I had one!!!! Like I said, the pro's leave it rougher than a corn cobb, and they make a bunch of power.
I wish someone would do a side by side dimple deal on the intake side and pop it on a dyno. I think it was Bob Glidden that did this in the late 70's or early 80's? Never much heard much more about the "golf ball" set up in a long time. Makes sence to me that it works..............but why don't you see the big 3 doing it then? Dosen't work? Too expensive? I sure wish I knew for sure. I still hear about "turtles" in the intake every now and then. My buddy is going to turtle his intake. Don't know if it will make more power?

 

DCryder ... Spot on about the water & boat! That one I understand from years of boating... your exactly right.

But now youll have to excuse my lack of knowledge....?? extrude honing ?? ... Whats that all about? Is that like the putty with the media in it and they push it through the intakes to smooth it out?
Its kind of like sandy playdoh... ever heard of that ?

When you say fuzzy what exactly can I relate that to?

 

Exatcly what I am trying to get at. I used a little dremmel stone grinder which left dimple like textures throughout the intake. If I had used a 60 grit sandpaper bit it would have been smoother, so there's your idea. I don't know if i have max increase, but what I do have is a lot better than stock. Hope this can help someone.

 

How much material is left after you remove the bumb inside?? I would think the risk of grinding a hole through is pretty high?

 

Actually I did the whole feel for heat and vibration thing, and by the time i was done, You couldn't tell the difference between the top and the bottom (where the bump was) and I still didn't feel like i was close to going through.