holy crap, i gotta get my shuvvel out but i dont want to make a new thread since this one has a lot of good shit in it. I've heard its bad to polish the head when doing a job. Doesnt make any sense to me why a shinny mirror finish would not be better compared to a rougher brushed finish.

atomization.

So you want brushed aluminum then?

Google image search "beating a dead horse"

whos horse? Also what color horse are you talking about?

:facepalm:

From what I understand shiny is good for exhaust because carbon does'nt build up as easily.

But with a shiny intake the fuel will "wet" the surface of the port. Thats why most porters like a textured finish on the intake ports either brushed or even better glass bead blasted.

Shiny intakes are for ricers.

My friend was telling me that the texture on the intake is for turbulence. It causes the fuel to mix more evenly. Think of the aerodynamics tests they do on cars where you see the smoke in a flat line over smooth surfaces. If it doesn't have turbulence, then it doesn't mix with the rest of the air very well.

Not sure that is the case, at least, completely the case. A surface that is too smooth allows fuel to stick to the port walls, causing the fuel to bead into large droplets. When those large droplets enters the combustion chamber, the mixture does not explode as violently as when the fuel droplets are very small.

When Braineak says atomization (a few posts up), he means very small fuel droplets.

correct, ever since i asked that question in another search i dropped into a website that explained it very well. Ever drive on the highway in the rain? you notice the droplets on your hood never really dissipate unless the hood gets too hot. Its the same thing inside the intake side of the manifold if its polished smooth. The big drops form and never mix well with the air hitting them.

I had head work done on a previous bpt but couldn't tell you what made the power (I'm thinking it was mostly the compression/cam timing bump).

Shaved 0.013" (to straighten), intake port matched, casting lines/imperfections removed, 3 angle grind, back cut. I did the casting lines/imperfections and port matching as well as porting the wastegate on my tiny IHI.

This made the car feel significantly faster at 8psi (my low setting) and a bit faster at 14psi. The work I paid for included 6 new valves, I took the lifters and cams out first and put them back in, for $400.

Rough intake, smooth exhaust...

so the reason you want rough runners is indeed for turbulence, but it's not necessarily for atomization.

it's more for the reason a golf ball has dimples.

when you have fluid flow (air, water, air/fuel vapor) across a smooth surface, the first layer of fluid immediately against the smooth surface does not move. it sticks and is stationary.

the subsequent layer slides across the first layer and so on.

in reality, there's no "layer" per se, but a gradient of flow velocities from the smooth surface to the maximum flow speed path. all that "sliding of layers" is subject to friction just like any two solid parts sliding across each other.

when you dimple / rough up a surface, it does indeed cause turbulence at the surface. and that turbulence acts like a bunch of little fluid ball bearings and breaks up the sliding layers. since you dont have smooth sliding layers anymore, your friction goes down.

hence why planes often include a feature to fuck up the boundary layer near the leading edge of the wing and reduce drag.

So, kinda like why leaving the tailgate up on a pickup is better. The air flows over the circulating air in the bed. <- Great Mythbusters episode btw.

^ They also did one on the "dimple effect". Dimpling a taurus like a golf ball resulted in a ~15% mpg increase and a funky looking car.

According to one big league racing motorcycle engine builder, dimpling the intake runners like a golf ball surface improved power a lot on the dyno. But, they did not use it as it was a lot of labor and took a long time to do it. Another trick is to dye the fuel and you can later remove the runners to look for fuel condensation on the walls and flow patterns.