Tractorsport Flowbench Forum Archive

Posted: **Mon Dec 25, 2006 10:51 pm**

I have just built a basic orifice flow testing unit capable of 10" W.C. differential. Crude but effective. I'm using it for flow testing Harley Davidson heads.

Its working and I have been able to verify its accuracy using various sized sharp-edged orifice plates turned on a lathe. Using the spreadsheet "orificeflowinapipe.xls" I get excellent agreement with my inclined manometer to the theoretical calibration values. Many thanks to whoever set up that spreadsheet. Also, thanks to this board in general, the info here has helped me a lot.

Now in experimenting, I notice that I can get dramatic flow improvement by shading the Harley intake port with a curved object, or with the palm of my hand. Stands to reason, since the Harley intake port is a flat surface with a sharp-edged round opening. By attaching a stock Harley intake manifold to the head I get better numbers than without, but I can still improve on the flow by shading the intake.

My question is, what type of intake pipe should I be using to get best and consistent results, or more to the point, how to get results closer to what the pros are publishing for stock unported heads. I notice some of the pro porters say they use a 3-1/2 inch intake with a 3/4" radius. I envision a horn-shaped tube designed to minimize turbulence as the air is taken in. Is this some sort of optimal shape that is used to get standardized results?

Dave

Posted: **Mon Dec 25, 2006 11:23 pm**

Unless you know exactly what the "pros" are using and your bench is calibrated to read the same as thier's is you can't compare the numbers. Setup a radius inlet and use it everytime the exact same way when you test a head and your numbers will show you the change in flow, and the change in flow is what you need to be concerned with. Not comparing your flow numbers to the "pros" numbers.

You will find some indepth discussion on this subject here on the forum it has been discussed at length in the past.

Posted: **Tue Dec 26, 2006 4:06 am**

What do you mean by "shading the intake", I don't understand that term?

I agree with Bruce 100%. You're numbers are releative to your bench and your test conditions. That's not to say that your bench wouldn't yield values obtained on a SF110 or very close to them though.

You have to duplicate the test process before you can compare with confidence.

Gofaster is a member who focuses on HD porting. He'd be the one I'd expect to have some input for you on HD flow setups.

His website is

I flow my motorcycle & ATV heads using the OEM manifolds with and without carbs attached. The more you can duplicate the true path of the flow, the better IMO.

You can pick up CFM with a radiused intake and you should always use one that allows you to be repeatable. To me, clay doesn't cut it but there are a lot of good head porters that do use clay to mock up the intake radius.

Edited By larrycavan on 1167120731

Posted: **Tue Dec 26, 2006 7:10 am**

Thanks Bruce and Larry. I did a better search and found some good discussion about modified inlets.

For lack of a better term, I used "shading" to describe how flow can be improved by placing a curved object right at the edge of inlet of the head. For the Twin Cam head, this seems to produce a surprising jump in flow when a 3/4" to 1" tube placed just below the bottom of the port. Probably similar to the effect of flow balls I read about.

I'm not really concerned that much with the "pros" work, I just think they are using an ideal inlet tube design that I'd like to know. Could cut down on a lot of experimenting you know.

Thanks for the help. Great forum.

Dave

Posted: **Tue Dec 26, 2006 6:42 pm**

If you do a bit of wool tuft testing around the intake port entry, you will quickly discover the turbulence created by that sharp edge ! That wool will flutter like a flag as highly turbulent air tumbles into the hole.

Any radius is better than none, but beyond a certain size, the extra improvement will be minimal. A perfect port entry test fixture should make your wool look like a rigid piece of bent wire with zero fluttering where the air smoothly accelerates into that port entry.

Another thing wool tuft testing will show, is that most of the air entering the port comes in radially from around the edges, and "falls over the edge" into the hole. Very little flow enters the port from directly in front. This usually comes as quite a surprise to most people, and is not at all what natural logic would suggest.

So the optimum testing setup may be a suitably large area flat metal plate, of sufficient thickness to accommodate a smoothly lathe turned entry radius. That should exactly match up to the inlet port entry without any step.

Wooden entry plates are practical too. Suitably contoured router bits can be purchased that will create a nice accurately rounded entry radius with minimum effort. It is a very easy way to make a whole range of adapters of consistent repeatable radius, even for rectangular ports.

Posted: **Wed Dec 27, 2006 4:25 am**

Posted: **Wed Dec 27, 2006 6:50 am**

Tractorsport Flowbench Forum Archive

Got my flow test unit up and working