Port texture and velocity

[RCJ]

When going from a smooth port to a textured port, does the average velocity change?

[David Redszus]

When going from a smooth port to a textured port, does the average velocity change?

If the fluid flow is through a straight tube, there is very little change in velocity; a result of boundary layer effects.

If the tube is curved, the air mass will impact the walls and a textured surface will result in a higher friction loss.

[mag2555]

Velocity would only change overall if the flow rate has changed.

[SpeierRacingHeads]

Locailzed velocitys will indeed change, kind of why you do it.

[Stan Weiss]

Chad,
Can you post some before and after cfm and velocity. We can then calculate what change in effective area the air is seeing.

Stan

[SpeierRacingHeads]

Chad,
Can you post some before and after cfm and velocity. We can then calculate what change in effective area the air is seeing.

Stan

I did this honest hillbilly test.

http://speierracingheads.com/burr-vs-60-grit.html

[trmnatr]

Chad,
Can you post some before and after cfm and velocity. We can then calculate what change in effective area the air is seeing.

Stan

I did this honest hillbilly test.

http://speierracingheads.com/burr-vs-60-grit.html

Great info Chad, would be interesting, would my iron heads be different such as like seeing bigger gains with the burr?

[ClassAct]

Chad,
Can you post some before and after cfm and velocity. We can then calculate what change in effective area the air is seeing.

Stan

I did this honest hillbilly test.

http://speierracingheads.com/burr-vs-60-grit.html

Interesting for sure. I may have to do a rethink on some things. The only issue I have is getting the burr finish correct. I can't duplicate what your finish looks like.

[digger]

i would have expected that the measured averages to be the same if the flow is the same

[David Redszus]

i would have expected that the measured averages to be the same if the flow is the same

I would expect the flow rate to be somewhat lower with a textured surface due to an increase in the friction factor.

[RCJ]

I'm working with and engine that by rule has a primary header smaller than the exhaust port.My thinking was that texturing the exhaust port would increase velocity thru the center of the port.Because of the small header I'm not using the whole port anyway.
Didn't work , small lose in power over polished port in A-B-A test.
I tried several ideals with poor results .The only thing that shown results is polishing the header till it is so thin that cracking is a problem .

[SpeierRacingHeads]

I'm working with and engine that by rule has a primary header smaller than the exhaust port.My thinking was that texturing the exhaust port would increase velocity thru the center of the port.Because of the small header I'm not using the whole port anyway.
Didn't work , small lose in power over polished port in A-B-A test.
I tried several ideals with poor results .The only thing that shown results is polishing the header till it is so thin that cracking is a problem .

Texture is totally wrong on the exhaust. The FASTER the localized airspeed, the more polished it should be. The SLOWER the localized airspeed, the rougher it should be. Remember, at the wall the air velocity is zero or near zero. The viscosity of the air is holding onto the wall so, the faster the air gets, the thinner the boundary layer gets. Regardless of surface texture. The surface texture is all wet flow any way. IMO around 1% flow loss is attributed to frictional wall drag of the boundary layer.

[digger]

i would have expected that the measured averages to be the same if the flow is the same

I would expect the flow rate to be somewhat lower with a textured surface due to an increase in the friction factor.

The flow numbers were the same though so the average velocity is the same since the area is for all intensive purposes the same

[David Redszus]

i would have expected that the measured averages to be the same if the flow is the same

I would expect the flow rate to be somewhat lower with a textured surface due to an increase in the friction factor.

The flow numbers were the same though so the average velocity is the same since the area is for all intensive purposes the same

Surface texture has an effect on flow coefficient in curved sections at higher velocities. Low pressure ratio measurements are quite inaccurate and should not be trusted for critical work.

[RCJ]

Does the boundary layer have any insulation properties?