Why an engine makes more power off a burr finish

[F1Fever]

This is the finish I like for performance, I go a little rougher for a lot of street driving.

[jpankey]

The way it was shown to me years ago was like this . The concrete shop floor finish was glass smooth .The concrete drive up to shop had a rough broom texture. The demostration took a glass of water and slung it so that it had momentum on the shop floor the water puddled into one large puddle in one area but on the driveways rough texted surface the water broke up into individual puddles and droplets. If someone already had posted something like this I'm sorry I got board reading all posts and must have overlooked it .

[BlackoutSteve]

The theory behind shark's skin.
Shark skin is rough like sand paper which creates a thin layer of turbulence against the shark's body as it moves through the water.
This thin layer of turbulence provides a slippery "bearing" between the shark and the water surrounding it when moving, and is said to allow them to move faster through the water with less resistance.
Makes sense to me and I think the same theory applies here.

[140Air]

The way it was shown to me years ago was like this . The concrete shop floor finish was glass smooth .The concrete drive up to shop had a rough broom texture. The demostration took a glass of water and slung it so that it had momentum on the shop floor the water puddled into one large puddle in one area but on the driveways rough texted surface the water broke up into individual puddles and droplets. If someone already had posted something like this I'm sorry I got board reading all posts and must have overlooked it .

Then they put a fan on it and demonstrated how fast the water evaporated.... only they may have used sandpaper or they may have given the example of rocks on a roof. The principle was that the much greater surface area and perhaps the boundary layer turbulence of the rough over the smooth promoting the faster evaporation. No question (except that water on a smooth surface shows its great surface tension, compared to gasoline, and tends to merge). The issue is that the rough surface is not best for airflow (except for high curvatures where flow separation occurs and a rough texture can delay this) versus the promotion of evaporation of "wall fuel" making for a cleaner burn (very helpful if you are running stoich or lean and, IMHO, not significant if you are running rich and dirty -as in making power).

[twl]

I don't see where this becomes a flow reducing issue.
I have no problem making enough flow AND having the texture that I need.
What is stopping people from making the port flow enough and have texture too? In fact, it appears that they ARE getting enough flow and having texture too.
I fail to see how this is inhibiting flow in any way?

[BrazilianZ28Camaro]

I'm wondering if somebody has wet flow tested a clear plastic tube firstly all smooth inside and after that texture just half the wall along its lenght (so the wet flow behavior can be seen) at 3-400 fps and picture it with ultra high velocity camera

Would be revelating I guess.

Hope I'm not way over my head.

[Erland Cox]

It lowers flow if applied in high velocity regions like the SSR but that does not necessary means that it gives less hp if used there.
I once tried a rougher finish in the Venturi of a restrictor and that was a disaster.
It sounded strange and making it smother gained more than 10% in flow.
This was not even a burr finish but 60 paper versus 120 paper.

Erland

[BrazilianZ28Camaro]

It lowers flow if applied in high velocity regions like the SSR but that does not necessary men that it gives less hp if used there.
I once tried a rougher finish in the Venturi of a restrictor and that was a disaster.
It sounded strange and making it smother gained more than 10% in flow.
This was not even a burr finish but 60 paper versus 120 paper.

Erland

I'm not sure , but maybe the die on the boundary layer could be pictured in the case I proposed above?

[Erland Cox]

Try to put the question another way because I don't understand it.
OK, I think I do now, try it in a clear plastic tube?

Erland

[Unkl Ian]

Darin did testing with dry ice, to help visualize flow patterns.

[The Radius Kid]

This does get involved,doesn't it?
What texture do you use and under what conditions?
Where to texture and where not to?
It sounds like one answer is not the be all,end all.

[BrazilianZ28Camaro]

Try to put the question another way because I don't understand it.
OK, I think I do now, try it in a clear plastic tube?

Erland

Yes, take a clear tube ( so you can see and picture whats happening into it) ,bolt it on a wet flow bench, test it smooth first, then do a texture just on half its I.D. along its lenght, this way you can still see whats happening to the "ink" on the air stream and at the boundary layers into the tube.

Testing this at high air velocities would be interesting, but you must be able to picture it.

[Larry Widmer]

F16's painted in the Thunderbird paint scheme (gloss), had more range then the planes painted in 36270, 36375, and 36118 (which had some texture). I was amazed at the performance differential that we found between the two planes identically outfitted....

[MadBill]

Presumably a few more MPH also?

[The Radius Kid]

F16's painted in the Thunderbird paint scheme (gloss), had more range then the planes painted in 36270, 36375, and 36118 (which had some texture). I was amazed at the performance differential that we found between the two planes identically outfitted....

Interesting observation.
When you speak of "range",what kind of airspeed were you speaking of and did or didn't it hold true for all airspeeds?