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Posted:
Sun Jan 30, 2005 9:16 pmby bruce
Ok, I've actually had some time this past week to do some testing on my own parts and I've run into a little problem, turbulence! My shortside radius has alot of turbulence from the turn back into the port about 1/2". I've raised the turn with some modeling clay and that took some of the turbulence away, what are some other tricks to try and smooth out an area with "wild" air? General ideas on what might help, I know each port design is going to be different and I'm gonna have to do some playing to figure this one out since its not your everyday standard engine design (old flathead).
How much effect does a wider seat play? I've spent alot of time this week on valve face widths and their effect on flow along with back angles and have found an additional 10% from what I did have. I'm planning on playing with seat face widths next.
Thanks in advance for any tips . . . and for those of you who would rather not pass along and secrets in public my private messages are another option 
Posted:
Mon Jan 31, 2005 3:50 pmby RRBD
Bruce,
Fill it in. Use your velocity probe, it will tell you. Fill in the dead spots for starters. If you can add material and not lose flow you are improving the port from a velocity standpoint. Make sure your port isnt too big, there is alot of info online on port design. crunching the numbers works. Always remember "velocity is king"
Posted:
Sat Feb 05, 2005 1:13 amby SWB
Are you checking with your manifold in place? That can make a difference. I worked with a head one time where I figured I had the turbulence problem taken care of after a lot of time and energy spent and then bolted the manifold on and realized I had wasted my time! I'm a lot more careful now about how I go about testing things. It can be pretty tough getting a long enough wand down the port to see how things shape up.
Another thing to try (yes this will take a long time) is to blow in the inlet side and view the airflow from the cylinder side. You can use a probe around the valve seat. You can also use string or thread stuck in short tufts around the periphery of the valve head or that general area. Try introducing some media of some kind into the airflow also. The key is to not use too much.
Think about the lengths of the different port surfaces up to the seat. The more equal the less general turbulence effects you are likely to generate. I will also say from experience that as you get these lengths closer to equal, their lengths become more sensitive. Just small differences start to make a large change in flow performance. (especially true along shortest path)
Keep in mind also that your short side radius may not really be the shortest route to the cylinder in your application! You may have to port appropriately. (ever seen a ford flat head?)
SWB
Posted:
Sat Feb 05, 2005 9:42 amby bruce
What I actually did was cut a cylinder head out of clear acrylic so I could see what the flow was doing, like you said using thread. This also lets me see where the wand is located in relation to the valve seat. I do not have a manifold to worry about, the carb just bolts to the block. I was using a radius plate on the port entrance. I did not try it with the carb bolted on to see if that changed it (duh). I took the block off the flowbench this past week and I want to re-clay it back up after cutting some new seat profiles. I'm thinking my seat profiles I now have are causing alot of problems as the are pretty humble the way they were done.
All in all I have found some pretty good gains from what I had "thought was working". I can see its going to just be trial and error to find the best combination. After seeing what the flow is doing my mind has changed on how I was thinking. One thing I had thought was stem smaller dia being better, what I have seen is back angle is more important than stem dia. 11/32 to 7mm didn't make a change but going with 5* difference on back angle made a world of difference!!