True throat/window, low port heads

[blaktopr]

With the completion of my bench and starting back up with cylinder heads, I been trying to wrap my brain around airflow dynamics in general and how it applys to porting. Trying to make a better decision through understanding than rather the "young" way as bigger is better. Just going to give a little that leads up to the topic.

I am trying to utilize what I learned, new theories, Pipemax, etc to an allready ported Pontiac cast iron head. I have a target, I unfortunately don't have any valve grinding equipment, done some work on the port,, and am not getting any good results in regards to cfm. Port shape and velocities look good to me but I am afraid that I will do something wrong while trying for the right profile.

Valve size currently is 2.12. Area below the seat is about 85% of the valve. With epoxy, the push pinch width and hieght were opened slowing down the air measure with a pitot. Speed over the ssr came down very little so that area was widened. Kept in mind port taper also. Speeds are measured and calculated to be very good with current thinking and Pipemax........BUT....

The port will not flow. No matter what, the port seemed limited somewhere. Probing and watching with visual tools, I watched where air wanted to go. Maybe because I can't work on the seats, I am missing something. But the flowpath follows to the window, valve or no valve, and not down to the throat size, but the shape of the opening if you looked down the airpath through the port. I tried more widening over the ssr and widened the bowl behind the seat and picked up a little flow. Larry and others mention how there is false flow especially over the ssr. But what about this.

There are heads that work well in a running motor when the valve/throat is opened more than the proper should be. Looking at the area on one plane shows it to be very large and not the correct way to increase flow. Follow the air on a low port head and the throat is reduced due to the angle of the approach. I probed both no valve and with valve at the throat which is larger csa than the rest of the port, and found airspeed to be close to or more than 350 fps in some areas. Not to mention, there is good airspeed also downward through the center odf the throat/bowl, and when probing also shows the "window" I am speaking of. Above or below or side to side, leave that area and speed drops.

The cast iron head has a velocity profile now that has fastest airspeeds closest to or at the throat. Is this why some low port heads work well with a larger valve/throat? Ask me questions if I missed giving some info. Plus I have notes on many tests. Looking to get some different perspectives instead of just doing things the same as others or blind by not thinking of airflow phenomenom.
Chris.

[106-1194218389]

[color=#000000]Chris,
Generally I try to get my throat below the valve about 88% to 89% on my 23

[blaktopr]

Hey John. I read your topic on your heads a few times. Lots of good info. I appreciate any input. My mind has so many things in it at once, thats why I am basically asking a few questions at once here.

I tried that move that you drew up this afternoon. There is barely any change. Still turbulent and still not the flow I am looking for for the combo I am designing it for. Let me try to break up my thoughts.

1) Even though air does follow the ssr and I can see separation starting through string bounce, it seems that the entire area is not being utilized. There is not much bias on the chamber side ssr radius but non turbulent air still follows to the opposite side. It seems the only work left I can do would be in the throat. It is hard on these heads to get the throat to 90% of the valve size at these valve sizes. I am allready thin as it is. Plus, if I were to do so, the csa will be again much larger than the rest of the tract. I do have to still experiment with seat angles. About 2.85 would be the csa at 90%. That is about .2 larger than I need for MIN csa according to Pipemax. The push pinch was opened now to 2.3 which does take into account the corner radius. I don't want to mess with upstream until I can make a change that can pick up flow. All changes upstream did not make any difference in flow. I do know that these heads would pick up bench flow numbers with a bigger valve but don't want to do it. I am trying to crate a good profile. But it seems that without it, it won't flow. Like I said, I do not have the means to play with the seats. Maybe someone can tell me if 30 to 40 cfm can be had with that. The seats on this test head are gone and is basically a radius. I did find a better flow curve with a different shape valve though.

2) That all leads me to this, and maybe Pipemax Larry or any others can answer this. In regards to the talk of oversized valves in some heads. Plugging some numbers into the Pipemax program shows HP and Tq relative to flow and other parameters. There are motors that utilize the larger valve/throat than the program predicts but still runs close to or on the number. Thats why I am questioning the large seat/throat combos that are found on some low port heads. I have these talks with a friend of mine who doesn't understand the things that we do, but sees the big valves work and I tell him that there is more to that. I would like to really believe what I am thinking is true and that there is more power to find. So far though, to test these things on my own bench/car, I am having the problem with my head's flow curve. Basically, I am trying to prove to myself that two heads with the same flow that the one with the better port profile will outrun it. What I read is one thing, what I can produce with my own hands is another.

3) Another funny thing with these heads I'm working on is that it seems that they don't respond to well to changes in csa's through the port unless you put something anywhere in the port. When I started, there were some dead areas. Now with a better profile (IMO) they don't flow much more, don't like anything to be added anywhere in the port, (causes a restriction), so it seems that the air is using more of the port. It does "sound" a little better. I need more motors for it to pull 28" plus so I can't try higher. If the air separates and goes turbulent, it doesn't go there as fast and hard as the original ported version. No flow balls will reattach the flow. Actually, if you put your hand under the head below the runner it will calm down. I got some pics and more info for later. Thanks
Chris.

[106-1194218389]

[color=#000000]Chris,
A couple of questions:
1. Does the flow go backwards at the convergence lift? That is when the curtain equals the valve area. In my case that was .512" lift. PipeMax will tell you when the convergence lift is. If you do lose flow then the SSR may be too bulbous or fat. I laid mine back and made the radius less sharp - a more gentle radius.

2. On the turbulance is you intake valve back cut and what is your seat angle on the intake valve. On my intake it was so stinking turbulant after .400" lift and nothing I did took it away. I then back cut the intake 35

[blaktopr]

John, the turbulence issue seems to be happening later in the lift range the more work I do. Initially it was .475 then up in .025 incriments until now at .575 That is the problem with some iron pontiac heads especially with bigger valves over stock, when it comes to the "fat" ssr. The seat is behind the ssr radius if you know what I mean, or I should say under it. I been trying to pull it back not to have that "overhang" , that must be why the turbulence is happening later. Getting close to water. Lots of Pontiac heads are casted a little different in regards to the seat positioning to the chamber/deck. Some better than others. I wish I can start with a small valve version which offers the straighter shot from the ssr to the seat. The problem with that though is the proper valve size in relation to the bore. Keep the valve small, lets say 2.05, maybe 2.08 and the ssr is a better shape. But I will be running a 4.185 bore and should be at around 2.12. Open the head for a 2.12 and now you are back under the ssr.

I hear you with the cuts on the valve. The valves that came with the head has two backcuts, very thin seat cut. Tried a valve with no backcut and shorter tulip height and the head holds back the turbulence a little. Tried a valve with a wide seat cut, small 30* backcut and even shorter tulip hight and it helped flow a little and held the turbulence to the .575 number. I do believe once I can do the seats the head will respond. I got beat out again on ebay for a seat grinder. So I continue to wait.

Example of the large valve deal here. E-head with a 2.19 valve. 2.20 at pinch with radius included. 2.95 at ssr with radius included, haven't measured the throat but looks to be about 90% of valve. Cfm is 316. Pitot speeds high at pinch, calculated I think I got 395. But these types of heads make good power and within Pipemax parameters. Seems the opposite thoughts of port designs works with these.. Thats why the question of the real window/throat.
Chris.

[blaktopr]

Here are a few pics of some roughed in shapes.

[blaktopr]

another

[blaktopr]

looks a little strange

[blaktopr]

maybe this better

[blaktopr]

valves, wrong pic oooppps. Thats secret stuff... SSSSHHHHH

[blaktopr]

valves right pic now

[larrycavan]

[106-1194218389]

First of all, What in the heck are you doing up so early Larry! Tom, Larry is right on the money here. I have been also talking with Larry Meaux on some Chrysler 360 style heads for NHRA Super Stock. He said that he actually had to take some CFM out of the heads to get them to perform. He could actually get the heads to flow 270 cfm but then the speeds were too fast and the car slows down. When he gets the heads back down to 260 cfm then the velocity is inline and the car goes faster again. That is only 10 cfm but shows how important velocity is. Larry C hits it right on the head when he says there is too much focus on just cfm. That is why I went to the expense of doing those port molds. I needed a way to "accurately" measure the MCSA and where in the port the MCSA was. I should have been clearer on what I was doing when I post all that info on my heads. I was mainly checking velocity in the port and did not really care that much about CFM. On my cousins Brodix heads they had a ton of cfm but were way too fast for what he wanted to do. We had to enlarge the ports a lot at the pushrod pinch and some at the SSR to get velocities in line. Guess what? No gains in cfm but we have a bushel basket of aluminum grindings on the floor now.

I have to agree with Larry on the track is the best dyno. And do not be afraid of failure as it is part of the learning process. We have a whole garage full of parts that did not work, but should have. ;-(
John

[larrycavan]

John,

You can use the formulas in PipeMax to get your CSA.

Average_CSA = ( Flow_CFM * 2.4) / FPS

Put your pito dead center of the area and use the above formula. Much faster and easier than port molds.

At that time of morning, I'm already on my second cup John.....



Edited By larrycavan on 1226356193

[blaktopr]

Don't get me wrong guys, I fully understand the importance of shape and the speeds through the port. That is why I went through the lengths to raise and widen with the corner radius in mind, parts of the port to calm down the speeds and to achieve the fastest at the seat /throat. So far I am happy with the results in regards to speed. Even probing at the exit past the valve, before the valve, above it, now have the speeds there faster than at the pinch and the peak of the ssr is the only place where you see close to 400fps. I was only looking at cfm demand with rpm and piston where I would like the numbers a little higher. Right now, I am about 267 cfm with nice port velocities. I was trying to get a little more for this 462 motor. You are right about testing in the car and during the work on these heads felt that it should perform very well regardless of cfm. I also just needed a little kick from guys like you to keep me on the track of a correct port profile. The brain goes back to caveman mode when you stand in front of a bench. ( Insert Tim Allen grunt here)Following with your comments, I am one of those guys like yourself that questions other heads out there in the marketplace that have IMO, bad port profiles. But then I am told they have more experience and have probably tried it all. I am going to measure up the runner tonight and give some local and calculated airspeeds and flowcurve to post here. I don't want to know what I can do, I just want to discuss how the air behaves, have you guys keep me in check, and learn for myself, if you know what I mean. I like the discussion of the science of it, then formulate my own conclusion. That is why I kept it here. I want to be able to come up with the answers through understanding what is in front of me without to much outside influence on tricks. I like hearing what doesnt work and examples of how airspeed vs flow effected a running engine. I don't want to hear, add 50 thou on the top cut, or something like that. Thanks guys, those answers are what I am looking for. Any technical, airflow property science stuff is appreciated too.

Jfholm, I'm going to call you Peter, since you called me Tom

Chris.