ports to big? Then what?

[laser3kw]

Greetings to all! I have lurked about for a while and find this to be about the only site that talks about airflow with any candidness. I hope this topic will stimulate some good discussion.
As an introduction of myself, I am inquisitive by nature,and an enineer by profession. I have been in the field of performance, as a hobby / time consuming love, for around 25 years, the last 10 of which I have owned a Superflow 110 as well as other speed items (shop equipment, a water brake dyno and an interia dyno , low hp applications).
I have dabbled in porting, mainly in the area of single cylinder motors. The brunt of my knowledge is the basic shaping for better flow. The rules generally kept me from furthur modifications.
I now am persuing the automotive realm. My first project is the disection of a Ford v6 head. After making the initial measurements at .050" lift increments, I found the flow platues at around .300", and gains only an additional 10% up to .500". This tells me that the head is throat resticted and could stand a larger valve. But my concern went immediately velocity.
This is where I approach a new area. I really have never explored the velocity profile of a port. So what do I concentrate on and what equipment do I use? I see some of the items, software and hardware mentioned here and I am willing to step up to that level. Any toughts?
As my example goes, as I deleved into this mystery, I probed a little with a homemade verticle u - mamometer and a straight probe and a u probe. I am more confused. The u shaped probe showed literally no positive pressures but negitive. The probe is u shade with the opening facing the airstream. Another thing I found curious is that as I applied clay into the port, I could fill nearly half the port and not have an impact on overall flow! This leads to my topic title. Does this indicate the port SHOULD be filled in? If I reduced the port volume and do not impact the flow through the lift curve, wouldn't velocity increase? And won't that be good for low speed cylinder filling and ulitmately fuel economy and low speed torque? This head would be used on a street driven vehcile with the interest of improve gas mileage and good lowend torque . The motor would never need to produce power at or above 6000 rpm. And, according to the CSA calculator, the port should choke at 8100 rpm (if that is what the calculation provides - an rpm figure). So where to from here? That is the intriguing part of this - the problem solving.

[Shawn]

There are a bunch of factors that play into your determination of port size,velocities, and valve sizes.Here's a few things that are needed to get you in the ballpark-
What type of head is this?
Bore size
wedge head?
Current valve sizes
chamber shape
valve angle
throat area currently
short turn area
smallest port restriction area and location
port floor height
do you know how much metal you have in the port and bowl area's?
With your "u" shaped pitot, if i understand correctly, you getting number that show less that 1 on your manometer with the opening pointed into the flow stream? If so, you need to switch the hoses around on it. Without knowing the info above, a guess at your problem would be short turn related. If you can get those velocity numbers at the short turn, that would help a bunch.
shawn

[larrycavan]

laser3kw

First, welcome to the board!

Make sure your pitot is hooked up so that the velocity measureing side is hooked to the high pressure side of the manometer.

Now, let's get you headed on the right path. As Shawn pointed out, there are many pieces of information that you need to consider for the overall design of the port for your engine. Rather than taking them all into individual account, I'll point you to some good links and give you some pointers that were given to me by someone who's work I have total respect for.

You want a good, accurate "J" bend pitot. Audie sells them. Dwyer also sells them. I purchased a customer bent pitot from Dwyer at a very good price. Audie's are more expensive but they are also smaller and allow you to get into tight places.

When you're working with the pitot in an intake port, a good rule to follow is this. If the velocity pressure exceeds the test pressure, the air speed may be too fast. It's port dependent..ie an old 2V wedge head isn't going to tollerate the air speeds that a modern 4V downdraft motorcycle intake port will tollerate.

Rather than going on about that, I invite you to go to Google.com and search using the following criteria,
"pitot site:speedtalk.com" without the double quotes.



I've linked it for you.

Read everything that Larry Meaux has to say about the subject.


Second, go to www.maxracesoftware.com and check out a program called Pipe Max. Get a copy.

Keep us posted on your results. I, for one, am always interested in ideas related to porting. I'd really like to see more discussion of it on this board. Flowbenching we've covered in great depth with the help of all the guys that hang around here. Porting discussions could use a shot in the arm... :;):


Larry C

[laser3kw]

[color=#000000]I knew this wouldn't be easy! But... I like to learn. I can answer a bunch of Shawns inquiries right off the bat:
Bore size =3.504
wedge head? no
Current valve sizes In =1.600
chamber shape = basic bathtub
valve angle= 1

[larrycavan]

Here's the velocity manometer setup for intake.

If the pitot is properly constructed it will have an impact tube and a static tube.

The impact tube will be the center one that pokes out into the flow. The static tube will be the outer one and has tiny holes evenly spaced and radially drilled around the tube.

The static tube hose connection generally comes out the side of the pitot and the impact tube connection straight out the back.

You connect the static side with tubing to one leg of the manometer and connect the impact side to the other side. The static pressure cancels itself out and you will be reading impact pressure [velocity] in inches of water on the manometer.

Fire up the bench. dial up your normal test pressure. In your case, probably 10" on a SF110. You'll have to pretty much be constantly adjusting test pressure as you move the pitot around in the port.

If you get into an area where the velocity manometer is reading higher than your test pressure manometer, the air speed will be too fast [generally].

To convert your inches of water to F.P.S [feet per second] use this formula. [Square Root of Pitot Pressure * 66.2]

Map the port and log your readings, then convert the data to F.P.S.

Here's a drawing from Dwyer. It's not bent into a J but the same principals apply.

[larrycavan]

Here's a clearer picture of the setup.

[larrycavan]

You've got to measure the port Cross sectional areas in order to achieve you goals in porting efforts. There are several ways of doing it. PM me with your email and I'll send you something to read.

Short side area is the CSA [cross sectional area] of the port at the bend in the floor where the air turns down to the valve. That area can be fast. Sometimes very fast and often needs a larger CSA in order to slow the air down to make the turn.

SSR - Sort Side Radius [or bend in the floor]
CSA - Cross Sectional Area
MCSA - Minimal Cross Sectional Area [smallest area of port]
Floor height - generally measured from the deck. It's relative for figuring such things as angle of the layback of the SSR.

Once you get your pitot hooked up properly and start playing around inside the port with velocity and CSA measurements, then going back in and either filling with clay or removing material with your cutter, the picture will begin to be much clearer in your "mind's eye".

Put the pitot dead down the center of the port, about half way in toward the valve. Let the straight portion rest on the port floor to anchor it. Then slowly rotate the pitot in small increments, left and right. Watch your manometers, keep adjusting test pressure back to your standard test pressure. You'll quickly get a sense of what's happening.

Try to measure the velocity at the apex of the SSR and you'll see it's likely highest in that area.

Track how much difference there is between the port floor and the roof of the port. Too much difference and the air will be separating on you.

Getting the pitot oriented so that it's pointing dead nuts into the air stream can be tricky. Rotate the hand held end around a few degrees laterally. Where you get the highest reading is when you're in line with the flow.

It's not easy at first. I takes a steady hand. Sometimes you'll wish you had 4 hands and 2 pairs of eyes. Get the bench set at a height that is comfortable for you to map velocity and hold the pitot steady.

If you have a friend that can write down the velocity pressures for you while you work the pitot and the flow control knob, it will go quicker at first.

I'm all digital so I just click the mouse and grab the numbers.

Hope this all helps you get going.

Larry C