Port and Polish by Comiittee thread (Cool pics throughout)
03-13-2008, 12:33 PM
#16
Nordschleife Master
WOW, $2000 for CNC porting, actually i'm not surprised.
I am not so interested in the porting but would love to see the ports on a CFD and those would be able to find all sorts of potential problems and take the guesswork out of the whole thing. Assuming the software is correct of course. I would really only be interested in CNC porting if the heads had gone through the CFD software and changes could be made that would show an improvement in the end on a dyno, then of course duplicated on the remaining 7 ports.
I am not so interested in the porting but would love to see the ports on a CFD and those would be able to find all sorts of potential problems and take the guesswork out of the whole thing. Assuming the software is correct of course. I would really only be interested in CNC porting if the heads had gone through the CFD software and changes could be made that would show an improvement in the end on a dyno, then of course duplicated on the remaining 7 ports.
03-13-2008, 12:35 PM
#17
Rennlist Member
Thread Starter
03-13-2008, 12:37 PM
#18
Rennlist Member
Thread Starter
03-13-2008, 12:42 PM
#19
Nordschleife Master
i always hear differing opinions on wether intake ports should be smooth or not so smooth as to produce turbulence to help with fuel atomization. Not sure what the current consensus is on this though.
I read an article a couple years back about a guy in i believe India of all places, that was producing a dimpled look on the combustion chamber much like a golf ball to help with fuel burn and get more power and better mileage out of his engines. I don't understand the science behind it but I will always remember it because it seemed like a very good idea and something i had never heard of before. The writer of the article was able to explain the science but i don't remember the arguments specifically but again they seemed to make some sense.
Anyone else ever heard of a dimpled combustion chamber design before?
I read an article a couple years back about a guy in i believe India of all places, that was producing a dimpled look on the combustion chamber much like a golf ball to help with fuel burn and get more power and better mileage out of his engines. I don't understand the science behind it but I will always remember it because it seemed like a very good idea and something i had never heard of before. The writer of the article was able to explain the science but i don't remember the arguments specifically but again they seemed to make some sense.
Anyone else ever heard of a dimpled combustion chamber design before?
03-13-2008, 01:09 PM
#20
Rennlist Member
In a four valve head I wouldn't worry about smooth intake ports. There's plenty of turbulence in the intake port to keep the fuel suspended in my opinion. My ports are smooth.
You can't port heads with a dremel tool unless you live to be 100 & don't care how long it takes. You need some 6" carbide burrs & a die grinder.
The 928 intake port shape is pretty good as it is. I just enlarged mine slightly & smoothed them out. But don't touch the short side radius!!
Hammer
You can't port heads with a dremel tool unless you live to be 100 & don't care how long it takes. You need some 6" carbide burrs & a die grinder.
The 928 intake port shape is pretty good as it is. I just enlarged mine slightly & smoothed them out. But don't touch the short side radius!!
Hammer
03-13-2008, 01:23 PM
#21
Rennlist Member
Thread Starter
Would this apply to me Hammer:
The back profile of an aftermarket valve doesn't have the factory valve's "ski-jump" ridge on the backside, so obviously, we couldn't remove it. In fact, back-cutting on the exhaust valve helps improve flow in both directions. So, as much as it helps low-lift flow out of the cylinder, it will promote undesirable reversion when used with high-overlap performance cams. Since exhaust flow from the cylinder is what we are after, looking for improvements to the exhaust valve's profile is not quite the same as with the intake. To help exhaust gas flow around the face of the valve, and outward back across the seat, putting a radius on the valve margin is successful. We added a radiused margin to our new valves, and with no other changes, the results in Table 1, Column 6 were obtained. The radius margin brought low-lift flow back into line, to the tune of a 14-percent improvement at .100 inch over the out-of-the-box big valve. At this stage, we were well within reach of our initial goals, with a peak flow improvement of 25 percent over the stock port.
Adding Polish
Usually, surface effects on flow are minimal, and in the intake port, a rougher surface may even be desirable to help keep fuel in suspension, but it is a common modification to polish the exhaust port. Polishing the Chrysler big-block's exhaust port is a relatively quick process, thanks to the port's easy access and short length. Polishing helps to prevent future carbon buildup, and while working with the sanding roll, subtle additional areas to blend will show up, which also promote flow.
Adding Polish
Usually, surface effects on flow are minimal, and in the intake port, a rougher surface may even be desirable to help keep fuel in suspension, but it is a common modification to polish the exhaust port. Polishing the Chrysler big-block's exhaust port is a relatively quick process, thanks to the port's easy access and short length. Polishing helps to prevent future carbon buildup, and while working with the sanding roll, subtle additional areas to blend will show up, which also promote flow.
03-13-2008, 01:25 PM
#22
Rennlist Member
Thread Starter
In a four valve head I wouldn't worry about smooth intake ports. There's plenty of turbulence in the intake port to keep the fuel suspended in my opinion. My ports are smooth.
You can't port heads with a dremel tool unless you live to be 100 & don't care how long it takes. You need some 6" carbide burrs & a die grinder.
The 928 intake port shape is pretty good as it is. I just enlarged mine slightly & smoothed them out. But don't touch the short side radius!!
Hammer
You can't port heads with a dremel tool unless you live to be 100 & don't care how long it takes. You need some 6" carbide burrs & a die grinder.
The 928 intake port shape is pretty good as it is. I just enlarged mine slightly & smoothed them out. But don't touch the short side radius!!
Hammer
I was thinking maybe what I would do is very little on the intake port since it will have air being forced down its throat.
But on the exhaust side, radius the margin of the valve into the face for better flow, and then maybe smooth the port slightly.
03-13-2008, 01:27 PM
#23
Nordschleife Master
short side on the intake would be the bottom of the port on S4 heads.
If you look at the port, because its curved the lengths are uneven. The short side is the inner radius which is shorter then the wall of the outside port, thus short side. Its clear when you see a cross section of the port, or just imagine it from looking at the heads. If you start grinding into that then you can really trash your heads.
If youve never ported before, i would but a junk core head from anything 4 valve. BMW heads for V8's are pretty cheap, i had a bunch in LA but scrapped them, no one would buy them. I had one that had destroyed valves and had chunks out of the combustion chamber, that kinda head is the one you fool around with and get comfortable with, NOT YOUR 928 heads that are otherwise good.
Still if you don't know what your doing, you can very easily cause more damage then anything. I fooled around with it but never took it seriously because you need to have numbers to test before and after, aero stuff isnt just WHAT LOOKS RIGHT. There is more to it then that.
If you want a flow bench, look it up on Google, there are plans to make one at home that would work. I don't recall what it uses to measure airflow but it was a pretty big setup. But if your not going to put the heads on a bench to see before and after i wouldn't even bother messing with it. You dont just start grinding away what you think are restrictors in the ports, that will give you inferior heads very quickly.
If you look at the port, because its curved the lengths are uneven. The short side is the inner radius which is shorter then the wall of the outside port, thus short side. Its clear when you see a cross section of the port, or just imagine it from looking at the heads. If you start grinding into that then you can really trash your heads.
If youve never ported before, i would but a junk core head from anything 4 valve. BMW heads for V8's are pretty cheap, i had a bunch in LA but scrapped them, no one would buy them. I had one that had destroyed valves and had chunks out of the combustion chamber, that kinda head is the one you fool around with and get comfortable with, NOT YOUR 928 heads that are otherwise good.
Still if you don't know what your doing, you can very easily cause more damage then anything. I fooled around with it but never took it seriously because you need to have numbers to test before and after, aero stuff isnt just WHAT LOOKS RIGHT. There is more to it then that.
If you want a flow bench, look it up on Google, there are plans to make one at home that would work. I don't recall what it uses to measure airflow but it was a pretty big setup. But if your not going to put the heads on a bench to see before and after i wouldn't even bother messing with it. You dont just start grinding away what you think are restrictors in the ports, that will give you inferior heads very quickly.
03-13-2008, 02:22 PM
#24
Three Wheelin'
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If you want a flow bench, look it up on Google, there are plans to make one at home that would work. I don't recall what it uses to measure airflow but it was a pretty big setup. But if your not going to put the heads on a bench to see before and after i wouldn't even bother messing with it. You dont just start grinding away what you think are restrictors in the ports, that will give you inferior heads very quickly.
+1
I vote assemble, tune, and run the motor with 100% stock heads, as the stock 4v pent-roof design has been proven to support high levels of power.
Then purchase a few sets of trashed heads (per Ryan's idea) and begin experimenting, keeping in mind that velocity as well as CFM is critical. Build your own flowbench, find a used one, or pay a shop to test your heads. This is an engineering exercise: you can only proceed with data, and data is not verifiable nor efficiently gathered with the good old butt dyno.
You do not want to bolt some untested artful sculpting attempt to your motor only to find that it accidentally but drastically increases detonation by reverse-flowing exhaust gasses back into the chamber.
Once the experiments yield favorable results, purchase a good set of heads and take the experiment from the flowbench to the engine or chassis dyno.
Think of it as your Project 928: Phase II
03-13-2008, 03:33 PM
#26
Rennlist Member
Back cutting the valves will narrow the seat surface & increase chances of burning an exhaust valve. (although the fuel you're using also lessens the engine temps) On an all out motor I might consider it but the tradeoff isn't worth it if you're going to drive it on the street.
Smooth ports are more likely to puddle fuel on a carbureted engine than a FI engine like the 928. The injector sprays the fuel on the back of the intake valve. Not likely to cause puddling on the intake port walls. Actually removing the lip on the intake valve would diminish the turbulence that sweeps the fuel off the back of the valve.
Hammer
P.S. Exhaust reversion is also unlikely in a supercharged engine.
Smooth ports are more likely to puddle fuel on a carbureted engine than a FI engine like the 928. The injector sprays the fuel on the back of the intake valve. Not likely to cause puddling on the intake port walls. Actually removing the lip on the intake valve would diminish the turbulence that sweeps the fuel off the back of the valve.
Hammer
P.S. Exhaust reversion is also unlikely in a supercharged engine.
03-13-2008, 03:35 PM
#27
Rennlist
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I think I'm qualified to write about this. However, just because I think I am, doesn't mean that I actually am qualified.
What does that mean? It means that there is not a guide written for how to port heads...that I've ever seen...that is worth the price of printing it. It means that porting and polishing are kind of up to the "expert" that has the stuff in front of him. It means that the whole thing is kind of a "mystery" art. A bunch of trial and error....more error....in most cases.
The other problem is discussing this is that it is going to have to be very long and verbose to do anybody at home any good. And....I tend to be very verbose to start with! That comes from writing for magazines. They generally want filler (details.) Therefore, anything I write will be very, very boring for someone who doesn't care....and probably boring for those that do care!
The amount of information needed to help anybody at home is significant. There is no possible way to do this in one or two sittings. My eyes would fall out, my wrists would fall off, and you would all be looking for something to slash your wrists to end the boredom.
If you guys are game...I'll try. You'll have to tell me when I've bored you to death and ask me to stop. The first thing we will need is someone to tell me how to post pictures on this Forum. I'm too stupid to figure this out on my own. The instructions will need to be specific and detailed.
With pictures, I can show what tools work best, for me. I also have two sets of heads sitting here, waiting to be ported. They are scheduled to be started in 3 weeks. That will not happen. I've got 3 transmissions, 3 engines to finish, two engines to "trial assemble", a couple of race cars that need to go to the track, and a bunch of regular work to do before the heads will get touched. However, I can use those heads to show details.
I started porting heads when I was 16. Forty years ago. Volkwagen stuff. I started with a Dremel tool and used Cratex Rubberized Abrasives to polish. Very slow work. I burned out an untold quanity of Dremel tools, when I found a big electric tool at Sears. Worked much faster. Spun at one speed. Control was poor, as it was large. I found a variable speed controller for it. it worked pretty good, but was very tiring to control, as it was bulky and heavy. I burned out several controllers and tools. Finally went to air in about '72. Used one of those 110 volt Sears compressors. Melted several. They would actually smoke and burn up. I'd have to stop every few minutes and wait for the compressor to catch up every few minutes. I liked air. The tools were smaller and they had speed controls right on them. When I opened my shop in 1975, I finally got a 3 phase big conpressor and I could ruin heads at a much quicker pace. I bought my first flow bench in about 1980. This did not help with porting skills, but helped with shape and finish issues.
In that time, I've literally ported thousands of individual ports. I've ruined several, expecially in the "development" stage of working up a head design. I do not flow every port. This would cost a fortune, if someone actually did it. Generally, most of the people that claim they measure every port, lie about this. A set of ported heads, individually flowed, would cost more than the rest of the engine combined. It takes a bunch of time and effort. CNC stuff helped with this issue. Someone could develop a port design that worked and duplicate it many times over. Made individual port flow checking not needed.
The downside of CNC porting is that it is also possible to duplicate crappy ports......exactly! You can ruin ports in volume! However, the good news is that they will be ruined exactly the same way! So, the first step is to make a port that works, then duplicate it as close as possible.
To develop a port and CNC duplicate it for under $10,000.00 is not going to happen! The time required to do the development work, build fixtures to hold the head, and then program a 4 axis machine to dupicate that port takes a zillion hours. I think Mike Simmard can shed light on how tough it would be and the time required to fixture and program a port for machining. The good news is that the next 1000 would be quick and cheap.
That being said, here's what I won't do and what I actually do. I will not cut a cast iron port. Too slow, too dirty, way too hard. I do heads that I've developed and have patterns for. I don't have the time to develop heads that I've not worked up in the past. When I need a trick head for one of my big blocks Chevys, I call and buy heads from the best people I can find. I like Air Flow Research heads and I've had success with Dart.
So, what you think? Too boring? Too much effort. Let me know and I'll quit or continue.
greg brown
What does that mean? It means that there is not a guide written for how to port heads...that I've ever seen...that is worth the price of printing it. It means that porting and polishing are kind of up to the "expert" that has the stuff in front of him. It means that the whole thing is kind of a "mystery" art. A bunch of trial and error....more error....in most cases.
The other problem is discussing this is that it is going to have to be very long and verbose to do anybody at home any good. And....I tend to be very verbose to start with! That comes from writing for magazines. They generally want filler (details.) Therefore, anything I write will be very, very boring for someone who doesn't care....and probably boring for those that do care!
The amount of information needed to help anybody at home is significant. There is no possible way to do this in one or two sittings. My eyes would fall out, my wrists would fall off, and you would all be looking for something to slash your wrists to end the boredom.
If you guys are game...I'll try. You'll have to tell me when I've bored you to death and ask me to stop. The first thing we will need is someone to tell me how to post pictures on this Forum. I'm too stupid to figure this out on my own. The instructions will need to be specific and detailed.
With pictures, I can show what tools work best, for me. I also have two sets of heads sitting here, waiting to be ported. They are scheduled to be started in 3 weeks. That will not happen. I've got 3 transmissions, 3 engines to finish, two engines to "trial assemble", a couple of race cars that need to go to the track, and a bunch of regular work to do before the heads will get touched. However, I can use those heads to show details.
I started porting heads when I was 16. Forty years ago. Volkwagen stuff. I started with a Dremel tool and used Cratex Rubberized Abrasives to polish. Very slow work. I burned out an untold quanity of Dremel tools, when I found a big electric tool at Sears. Worked much faster. Spun at one speed. Control was poor, as it was large. I found a variable speed controller for it. it worked pretty good, but was very tiring to control, as it was bulky and heavy. I burned out several controllers and tools. Finally went to air in about '72. Used one of those 110 volt Sears compressors. Melted several. They would actually smoke and burn up. I'd have to stop every few minutes and wait for the compressor to catch up every few minutes. I liked air. The tools were smaller and they had speed controls right on them. When I opened my shop in 1975, I finally got a 3 phase big conpressor and I could ruin heads at a much quicker pace. I bought my first flow bench in about 1980. This did not help with porting skills, but helped with shape and finish issues.
In that time, I've literally ported thousands of individual ports. I've ruined several, expecially in the "development" stage of working up a head design. I do not flow every port. This would cost a fortune, if someone actually did it. Generally, most of the people that claim they measure every port, lie about this. A set of ported heads, individually flowed, would cost more than the rest of the engine combined. It takes a bunch of time and effort. CNC stuff helped with this issue. Someone could develop a port design that worked and duplicate it many times over. Made individual port flow checking not needed.
The downside of CNC porting is that it is also possible to duplicate crappy ports......exactly! You can ruin ports in volume! However, the good news is that they will be ruined exactly the same way! So, the first step is to make a port that works, then duplicate it as close as possible.
To develop a port and CNC duplicate it for under $10,000.00 is not going to happen! The time required to do the development work, build fixtures to hold the head, and then program a 4 axis machine to dupicate that port takes a zillion hours. I think Mike Simmard can shed light on how tough it would be and the time required to fixture and program a port for machining. The good news is that the next 1000 would be quick and cheap.
That being said, here's what I won't do and what I actually do. I will not cut a cast iron port. Too slow, too dirty, way too hard. I do heads that I've developed and have patterns for. I don't have the time to develop heads that I've not worked up in the past. When I need a trick head for one of my big blocks Chevys, I call and buy heads from the best people I can find. I like Air Flow Research heads and I've had success with Dart.
So, what you think? Too boring? Too much effort. Let me know and I'll quit or continue.
greg brown
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
03-13-2008, 03:44 PM
#28
Rennlist Member
Thread Starter
If you have the pictures somewhere on an electronic file, disk, CD, hard drive, or memory card from a camera, you are at a good position. If its on the camera card, can you connect that chip to the computer or connect the computer to the camera?
In the case of the camera connection to the computer, you need the drivers for the computer to read the camera. Sometimes this happens automatically, sometimes not.
If the computer or disk has the pictures, this is better.
you go to www.photobucket.com and creat an account. Make a login and password as easy to remember as possible.
When you have the account (this should only take a few moments) you can upload pictures there from your computer. You would do this by clicking on "upload pictures" or some derivation of that. You then "browse" for the file on your computer drive or disk drive or wherever the pics are, and then click on something like "upload".
Then, you click on the "img" "tag" area of next to the photo that has been successfully uploaded, and simply past it into your message.
All the pictures above have been put on this thread in that exact manner.
Again , sign up here: http://photobucket.com/register/?link=topmenu
and you are on your way.
03-13-2008, 03:45 PM
#29
Rennlist Member
I for one don't think it's boring. I agree with your statements about porting having many answers. Like ideas, everybody may have a different approach to doing it.
I ported heads since I was young as well & I'm glad you brought up the 'tool burning' confession. It's nice to know I'm not the only idiot that burned up bookoo dremel tools!
Hammer
I ported heads since I was young as well & I'm glad you brought up the 'tool burning' confession. It's nice to know I'm not the only idiot that burned up bookoo dremel tools!
Hammer
03-13-2008, 03:49 PM
#30
Rennlist Member
Thread Starter
Back cutting the valves will narrow the seat surface & increase chances of burning an exhaust valve. (although the fuel you're using also lessens the engine temps) On an all out motor I might consider it but the tradeoff isn't worth it if you're going to drive it on the street.
Smooth ports are more likely to puddle fuel on a carbureted engine than a FI engine like the 928. The injector sprays the fuel on the back of the intake valve. Not likely to cause puddling on the intake port walls. Actually removing the lip on the intake valve would diminish the turbulence that sweeps the fuel off the back of the valve.
Hammer
P.S. Exhaust reversion is also unlikely in a supercharged engine.
Smooth ports are more likely to puddle fuel on a carbureted engine than a FI engine like the 928. The injector sprays the fuel on the back of the intake valve. Not likely to cause puddling on the intake port walls. Actually removing the lip on the intake valve would diminish the turbulence that sweeps the fuel off the back of the valve.
Hammer
P.S. Exhaust reversion is also unlikely in a supercharged engine.