Polished ports VS rough 'dimpled' ports
01-27-2003, 07:40 AM
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Drifting
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Polished ports VS rough 'dimpled' ports
Not seen a great deal of discussion or research o nthis, other than I know some people 'dimple' the region near the inket & fuel injector site to promote turbulent flow & better fuel/air mixing.
Any opinions on smooth vs rough for flow number or mixing??
Any opinions on smooth vs rough for flow number or mixing??
01-27-2003, 11:31 AM
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Geoffrey
I'm aware that the spray pattern of the nozzle, as well as fuel pressure at the nozzle are large determinants of fuel atomization. However, I'm interested in whether laminar or turbulent air flow conditions are preferred when designing inlet and outlet ports.
I'm aware that the spray pattern of the nozzle, as well as fuel pressure at the nozzle are large determinants of fuel atomization. However, I'm interested in whether laminar or turbulent air flow conditions are preferred when designing inlet and outlet ports.
01-27-2003, 02:57 PM
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John,
I know and have worked with exactly what your talking about. Its not a well know practice with Porsche folk. However, I have delt with the dimpling on things like you mention (such as on a complete set of piston tops). There are gains to be had (at least on an American V8) and I am sure that after extensive testing you could find gains in a Porsche version as well.
Most people just dont understand the advantages.
Currently I recommend ceramic coating and miscellaneous friction reducing coatings on a bulk of 911 parts. Perhaps I will dimple a few Porsche things in the future.
<img src="http://boards.rennlist.com/upload/dimpledpiston.jpg" alt=" - " />
I know and have worked with exactly what your talking about. Its not a well know practice with Porsche folk. However, I have delt with the dimpling on things like you mention (such as on a complete set of piston tops). There are gains to be had (at least on an American V8) and I am sure that after extensive testing you could find gains in a Porsche version as well.
Most people just dont understand the advantages.
Currently I recommend ceramic coating and miscellaneous friction reducing coatings on a bulk of 911 parts. Perhaps I will dimple a few Porsche things in the future.
<img src="http://boards.rennlist.com/upload/dimpledpiston.jpg" alt=" - " />
01-27-2003, 04:14 PM
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To get better mixture preparation use a better injector or a higher fuel pressure or change the injector's cone angle or its position in the inlet tract, or all the above 
. Creating turbulence in the inlet tract will drastically reduce flow (turbulence in the combustion chamber is another subject altogether, however), to maximise port flow it is necessary to optimise the velocity profile within the inlet tract which, generally speaking, requires a smooth reduction in cross sectional area as the valve is approached with the minimum reached a little before the valve and a slight increase up to the valve itself. Getting the profile right is normally a matter of plenty of time spent with a high accuracy CFD model followed by experimental validation and development on single cylinder test engines, before carying the optimum result across to the real engine.
. Creating turbulence in the inlet tract will drastically reduce flow (turbulence in the combustion chamber is another subject altogether, however), to maximise port flow it is necessary to optimise the velocity profile within the inlet tract which, generally speaking, requires a smooth reduction in cross sectional area as the valve is approached with the minimum reached a little before the valve and a slight increase up to the valve itself. Getting the profile right is normally a matter of plenty of time spent with a high accuracy CFD model followed by experimental validation and development on single cylinder test engines, before carying the optimum result across to the real engine.
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01-31-2003, 12:33 AM
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From <a href="http://www.theoldone.com/articles/d16a_head/" target="_blank">The Old one Head Porting D16A</a> For more see <a href="http://www.theoldone.com/articles/" target="_blank">Index of Old One's articles</a>.
</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The finish on the entire port is the result of "scrubbing" with 40 grit at 4,100 rpm. This particular finish promotes good atomization of the mixture. The finish tapers to 80 grit in the last .50" prior to the valve seat inserts.</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">From PowerNews/Mototune <a href="http://mototuneusa.com/homework.htm" target="_blank">Intake Porting Part 2</a> For more, see <a href="http://mototuneusa.com/thanx.htm" target="_blank">PowerNews Index</a>.
</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The next time you drive a car in the rain, notice that when the car is going 60 MPH, the rain drops go up the hood of the car at walking speed. That's because the smooth surface of the car creates what's known as a boundary layer, and the portion of that layer of air that's nearest to the surface is almost still.
The same thing happens inside an intake port. Except instead of raindrops, it's fuel droplets that will run down the port wall slower than the air. That causes a serious change in the fuel air mixture by the time it reaches the cylinder, ruining much of the engine's potential power.
Polishing the port walls will ensure that this happens.</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">
</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The finish on the entire port is the result of "scrubbing" with 40 grit at 4,100 rpm. This particular finish promotes good atomization of the mixture. The finish tapers to 80 grit in the last .50" prior to the valve seat inserts.</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">From PowerNews/Mototune <a href="http://mototuneusa.com/homework.htm" target="_blank">Intake Porting Part 2</a> For more, see <a href="http://mototuneusa.com/thanx.htm" target="_blank">PowerNews Index</a>.
</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The next time you drive a car in the rain, notice that when the car is going 60 MPH, the rain drops go up the hood of the car at walking speed. That's because the smooth surface of the car creates what's known as a boundary layer, and the portion of that layer of air that's nearest to the surface is almost still.
The same thing happens inside an intake port. Except instead of raindrops, it's fuel droplets that will run down the port wall slower than the air. That causes a serious change in the fuel air mixture by the time it reaches the cylinder, ruining much of the engine's potential power.
Polishing the port walls will ensure that this happens.</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">
01-31-2003, 03:27 PM
#9
RL Technical Advisor
Gentlemen:
Great thread and I am truly enjoying reading this.
There is some good information here and I am compelled to comment on some things in the context of 911 heads. I do not do anything else,....
1) Never generalize about what you read. Each and every head design and layout is different, and every engine design likes & responds to different things.
2) Boundary layer flow control is very important. Observe how many precision pitot tubes a professional head porter uses with his flow bench. Those things are NOT cheap and you gotta have them to see how the heads flow at all valve lifts.
3) Port entry angles, guide boss placement & shape and throat contour, from entry to valve seat, are all things to be tailored to the camshaft profile in use. There is little point in working on flow numbers at .500 of lift, when the cams you will use max at .440.
Engines are to be considered in the context of the whole configuration when deciding on what head flow attributes are needed. A few factors are:
1) Camshaft profile
2) Displacement
3) Compression ratio
4) Bore & stroke
5) Rod length
6) Valve size
As I hope you can see, this is a complex set of variables and there is no one-size-fits all. Porsche 911 heads are not the same as domestic engines and others, so be careful about generalizations,...
Lastly,.............As you have likely surmised, people who do this for a living do not reveal what they know,.........its the result of learning though thousands of hours on the flow benches, engine dynos, and ruining plenty of good heads in the process.
Great thread and I am truly enjoying reading this.
There is some good information here and I am compelled to comment on some things in the context of 911 heads. I do not do anything else,....
1) Never generalize about what you read. Each and every head design and layout is different, and every engine design likes & responds to different things.
2) Boundary layer flow control is very important. Observe how many precision pitot tubes a professional head porter uses with his flow bench. Those things are NOT cheap and you gotta have them to see how the heads flow at all valve lifts.
3) Port entry angles, guide boss placement & shape and throat contour, from entry to valve seat, are all things to be tailored to the camshaft profile in use. There is little point in working on flow numbers at .500 of lift, when the cams you will use max at .440.
Engines are to be considered in the context of the whole configuration when deciding on what head flow attributes are needed. A few factors are:
1) Camshaft profile
2) Displacement
3) Compression ratio
4) Bore & stroke
5) Rod length
6) Valve size
As I hope you can see, this is a complex set of variables and there is no one-size-fits all. Porsche 911 heads are not the same as domestic engines and others, so be careful about generalizations,...
Lastly,.............As you have likely surmised, people who do this for a living do not reveal what they know,.........its the result of learning though thousands of hours on the flow benches, engine dynos, and ruining plenty of good heads in the process.
02-03-2003, 07:20 AM
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Great replies guys...nothing like a brosd knowledge base....
..some of these are VERY good things to know when planning how to spend hard earned money!
..some of these are VERY good things to know when planning how to spend hard earned money!
02-04-2003, 07:03 AM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Chris Bennet:
[QB]From <a href="http://www.theoldone.com/articles/d16a_head/" target="_blank">The Old one Head Porting D16A</a> For more see <a href="http://www.theoldone.com/articles/" target="_blank">Index of Old One's articles</a>.
[QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">WHoa, someone quoting Larry. Do you visit our board much Chris? Heheh. Wow you're #390 here but only 137 posts. you're a lurker.
[QB]From <a href="http://www.theoldone.com/articles/d16a_head/" target="_blank">The Old one Head Porting D16A</a> For more see <a href="http://www.theoldone.com/articles/" target="_blank">Index of Old One's articles</a>.
[QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">WHoa, someone quoting Larry. Do you visit our board much Chris? Heheh. Wow you're #390 here but only 137 posts. you're a lurker.
02-04-2003, 09:20 AM
#12
Race Director
The idea behind a slightly rough surface and dimples are not the same. They may be similar in final results (best air-flow velocity and fuel mixing).
The rough surfaces are best in the intake ports. This removes the shear friction on the layers of air close to the contact surface. This friction is caused by the zero-flow layer directly in contact with the surface. Then as you move away from the surface, the velocity increases, but due to contact with the underlying layer, there's some friction and velocity differences. The speed function vs. distance away from the wall is a parabolic funciton with zero at the surface.
The rough surface is kinda like a whole bunch of Gurney flaps which causes a vortex on the surface. This vortex acts like a bunch of ball-bearings allowing the air layer just above it to flow at full speed.
The rough surfaces are best in the intake ports. This removes the shear friction on the layers of air close to the contact surface. This friction is caused by the zero-flow layer directly in contact with the surface. Then as you move away from the surface, the velocity increases, but due to contact with the underlying layer, there's some friction and velocity differences. The speed function vs. distance away from the wall is a parabolic funciton with zero at the surface.
The rough surface is kinda like a whole bunch of Gurney flaps which causes a vortex on the surface. This vortex acts like a bunch of ball-bearings allowing the air layer just above it to flow at full speed.
02-04-2003, 01:37 PM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by GhettoRacer:
<strong> </font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Chris Bennet:
[QB]From <a href="http://www.theoldone.com/articles/d16a_head/" target="_blank">The Old one Head Porting D16A</a> For more see <a href="http://www.theoldone.com/articles/" target="_blank">Index of Old One's articles</a>.
[QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">WHoa, someone quoting Larry. Do you visit our board much Chris? Heheh. Wow you're #390 here but only 137 posts. you're a lurker.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Hi "Trackula"
I guess I am a bit of a lurker. I spend most of my "board time" over on Pelican these days. Is there something I should know about this Larry guy?
Chris
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<strong> </font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Chris Bennet:
[QB]From <a href="http://www.theoldone.com/articles/d16a_head/" target="_blank">The Old one Head Porting D16A</a> For more see <a href="http://www.theoldone.com/articles/" target="_blank">Index of Old One's articles</a>.
[QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">WHoa, someone quoting Larry. Do you visit our board much Chris? Heheh. Wow you're #390 here but only 137 posts. you're a lurker.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Hi "Trackula"
I guess I am a bit of a lurker. I spend most of my "board time" over on Pelican these days. Is there something I should know about this Larry guy?
Chris
Rennlist Liftime Member #990415-1008
03-12-2003, 12:27 PM
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Dan Perez:
<strong> </font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by GhettoRacer:
<strong> </font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Chris Bennet:
[QB]From <a href="http://www.theoldone.com/articles/d16a_head/" target="_blank">The Old one Head Porting D16A</a> For more see <a href="http://www.theoldone.com/articles/" target="_blank">Index of Old One's articles</a>.
[QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">WHoa, someone quoting Larry. Do you visit our board much Chris? Heheh. Wow you're #390 here but only 137 posts. you're a lurker.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica"></strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Sorry about that...
Larry has been known to put a dimple here or there ( take a look here <a href="http://theoldone.com/articles/badtothebone/" target="_blank">http://theoldone.com/articles/badtothebone/</a> and page down a ways until you see the picture of the intake port, and launch). If Larry does it, I wouldn't bother "talking " about how it doesn't work, I'd rather be trying it to see how good you can make it work.
Here's a guy who likes to talk about how he does things "for a living" publically posted on the internet of all places. Another crazy Texan.
Dan
<strong> </font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by GhettoRacer:
<strong> </font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Chris Bennet:
[QB]From <a href="http://www.theoldone.com/articles/d16a_head/" target="_blank">The Old one Head Porting D16A</a> For more see <a href="http://www.theoldone.com/articles/" target="_blank">Index of Old One's articles</a>.
[QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">WHoa, someone quoting Larry. Do you visit our board much Chris? Heheh. Wow you're #390 here but only 137 posts. you're a lurker.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica"></strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Sorry about that...
Larry has been known to put a dimple here or there ( take a look here <a href="http://theoldone.com/articles/badtothebone/" target="_blank">http://theoldone.com/articles/badtothebone/</a> and page down a ways until you see the picture of the intake port, and launch). If Larry does it, I wouldn't bother "talking " about how it doesn't work, I'd rather be trying it to see how good you can make it work.
Here's a guy who likes to talk about how he does things "for a living" publically posted on the internet of all places. Another crazy Texan.
Dan