Topic: aerodynamics, boundary layers, Velocity profiles, and you

[COOKIESandBEER]

I am doing a port job and I'm not using a flow bench. As stated above removing to much material or doing it un evenly can ruin your head. But what you can do your self is smooth and match the ports. That means removing the rough spots and casting marks and matching the intake and head surface to reduce unwanted friction. I am no expert but i believe this can be done with positive results without using a flow bench. I have ported/matched my head and it is awaiting a valve job. Then i will see how things turned out. If you look at the before and after pics in my thread you can see the casting removed.
http://forums.sohc4.net/index.php?topic=56904.msg614354#msg614354

SMOOTHING the surfaces of your intake ports adds more friction, i know this sounds counter intuitive but air running over a surface creates friction differently than say the friction created by metal on metal contact. on a smooth surface the first layer of air molecules adheres to the wall causing a "velocity profile" which restricts airflow (imaging a funnel where only the air in the center can pass through freely). a rough surface on the wall will create what is called a boundary layer(same concept as dimples on a golf ball or high performance bicycle wheel) basically what this does is create a layer of turbulent air along the wall that prevents the molecules from adhering to the surface and creating a velocity profile(or at least to a lesser extent) allowing better airflow through the port. just like all things in life, too much of a good thing is a bad thing. if the surface is too rough and passes through the boundary layer into the air-stream it will negatively affect airflow, but this would have to be an extremely rough surface. the gains are minimal, but if your just into it or racing it may be something to think about. i dont mean to be a jerk, just trying to let you all in on some truth nuggets.

P.S. smoothing of the exhaust ports is usually done in an attempt to minimize exhaust by-product buildup.
One last thing all this it applicable to fluids as well, though i wouldn't recommend fiddling with your hoses and fuel lines haha.

[Pinhead]

PowreLynz.

[bistromath]

I'm sorry, but this old racer's tale just isn't true. Golf balls have dimples in order to "hold" the transition zone from laminar to turbulent flow further back on the sphere, by inducing turbulence around the ball. This reduces the ball's flight drag by shortening the separation region of vortices behind the ball, which create most of the drag of the ball's flight. Your ports are designed for laminar flow all the way through -- there is no separation zone here. Obviously in a real port there will be some turbulence, but separation zones of the sort we're talking about require a "dead spot" like the area right behind the valve stem. Perhaps roughing up the valve stem will help, but not the port surface itself.  Speaking simply, it makes no difference.

The "velocity profile" you're talking about IS the boundary layer, by definition. And if dimpling laminar surfaces would reduce drag, we'd see some really dimply-looking 747 fuselages. Dimply-looking space shuttles. Dimply gliders. F1 cars. The list goes on.

I've also heard that rough intake walls encourage fuel droplets to atomize. I don't know anything about the physics of atomization, or whether that's a problem that needs to be worried about or not.

If there's a real aerodynamicist in here, feel free to correct me. I used to design the electronics for unmanned aircraft, and when doing my Camaro's head I asked our resident aerodynamicist his opinion on the polishing "wisdom", and that's what he told me.

[Pinhead]

... I've also heard that rough intake walls encourage fuel droplets to atomize. ...

+1; QFT.

[COOKIESandBEER]

the effects are usualy measured in UNDER 1%, which is by most standards pointless to even be concerned about, but they are still there. you are correct about the golf ball, bicycle wheels/helmets, and ive also herd about the atomization of fuel thing. vehicles designed to have extremely low drag coefficients such as F1 cars and gliders wouldn't need dimpled surfaces as they are already designed to be extremely slippery in the wind, also the laminar flow principle is already used by aircraft in the laminar flow airfoil. i just wanted to start a fun conversation not an argument.

[Nikkisixx]

Holy crap!  Out of the gate and trying for 8 on his first post it is the cowboy called CookiesandBeer.  What next synthetic oil, dynabeads, coil relays, aftermarket ignition, and pods? 

In a past career 15-20 years ago, I was an ASE cylinder head specialist, working at various hi-po auto machine shops.  I worked for  and learned from some of the best, and ported a lot of heads using a flow bench and dyno.  I will concur that polishing for the sake of smoothing didn't really do much. <- Read "neither help nor hurt".  Just like any other sculpting/carving activity, you need to step down to a tool that removes less material when you fine tune.  This is why you see "polished" runners.   That and the fact that it has perceived performance  .

As for porting without some way to measure the effect of changes, you might as well also synch the carbs, set the timing, gap the plugs, and adjust the dwell by "feel".

Hand me the popcorn?

[Laminar]

http://www.thecarconnection.com/marty-blog/1037073_video-mythbusters-test-golf-ball-theory-on-ford-taurus

[camelman]

Cookies and Beer,

All I'm going to say is that you are wrong.  I appreciate your thoughts, and you are came to good conclusions with the info you had, but you are applying the principles incorrectly.  I did more fluid mechanics modeling than I care to think about while working at GE in gas turbine design, and learned a lot about fluid flow.  The boundary layer statements you made are incorrect.  Bistromath has it right, and some others have good comments.  Let's just suffice it to say that you want a smooth surface in your intake runners.

PM me if you want to talk about this on the phone.  I think an open forum causes way too much confusion for physics explanations.  For what it is worth, I'm glad you are interested in this subject, and I applaud your courage to dive into it like this.  I think you should have done more research though.

Camelman

[COOKIESandBEER]

hey camelman, id love to hear more about it ill be sure to pm you. thanks

-COOKIESandBEER