Airflow Question - Need an experienced opinion

[Dom G]

Now that I have my bench running but not totally finished I started doing some flow testing on a head.

Since I have zero hands on experience flow testing I wanted to ask some of the members here with practical experience how to interpret what I found with this head.

Here it is.

While testing the intake port with valve lift in .100 increments from .200 to .700, the flow peaked at .500, then went down slightly at .600 and .700. The head has relatively small runners (volume) but with fairly large valves. I tested at 28" h2o.

Is this simply indicative of a port's inability to flow any more due to limitations set by small runner volume as well as the need for the entire port from intake opening to the combustion chamber to be reworked?

Or does it suggest something else like turbulence, etc could be effecting it?

I would be interested in your thoughts.

Thanks.

Dom

[larrycavan]

Dom,

Glad to hear you're up and flowing!!! I knew you'd get everything dialed in...

You need to look at L/D values [lift/diameter] and the curtain area in order to properly evaluate what you're seeing. It's quite normal, I assure you. While flowing at even .050" or .100" increments is acceptable, using the L/D method puts things into a 'ratio' perspective and that's important to establish in order to perform comparisons.

It's commonly accepted that at about .25L/D, the curtain area becomes the limiting factor and the flow values will fall off. Using the valve lift to valve diameter ratio, you will quickly see how that theory applies.

Larry C

[Thomas Vaught]

Congrats on getting your bench going.

Purchasing a copy of the SF600 instruction manual for $35.00 would be well served too as it has a vast weath of info on what to do to run a proper test, the l/d philosophy Larry mentioned, and much more.

JMO

Tom V.

[gofaster]

Dom,

Glad to hear you got the bench going.

Ditto on what Tom and Larry told you. Flow rates at .100", .200".... etc. are more of a sales tool to give the uninformed a figure they can compare to the scuttlebutt they've heard or read elsewhere. If you don't have a SF manual, go to Speed Talk:



and search "curtain" or "window" ,etc. to get more good info.

[Mouse]

Dom,

Sometimes these "flow holes" can be an air detachment or trubulance problem in the chamber. By using a thread, you can find the spots where the air is clinging to the chamber surface or going turbulent. Creating a ridge or something to cause seperation or clean up trubulance will often clear up the problem.

[Mousehouse1]

Take a piece of welding rod or tubing of some sort and attach a piece of string to it. Then use it to tell you if there is turbulance in the port.

[Dom G]

Thanks for the helpful input everyone. I plan on pursuing a number of the suggestions made.

Dom