Debate - Why not to polish a head!
10-27-2008, 09:59 PM
#1
Senior Member
Thread Starter
Join Date: 10-01-06
Location: Maidstone, SK
Posts: 5,134
Likes: 0
Received 0 Likes
on
0 Posts
Debate - Why not to polish a head!
This is a carry over debate from another thread....
Why not to polish a head....
Many people claim this is a false phenomenon.... however, it has been flow bench proven to affect flow.
Although usually non-credible, Wiki has a good explanation on the subject.
LINK
Discuss!
Why not to polish a head....
Air doesn't like to glide along a metal surface.... but flows along itself.... so a slight roughness holds a minimal pocket of air along it, allowing for less friction in the intake path.
Many people claim this is a false phenomenon.... however, it has been flow bench proven to affect flow.
Although usually non-credible, Wiki has a good explanation on the subject.
Originally Posted by Wiki
The "Porting and Polishing" Myth
It is popularly held that enlarging the ports to the maximum possible size and applying a mirror finish is what porting is. However that is not so. Some ports may be enlarged to their maximum possible size (in keeping with the highest level of aerodynamic efficiency) but those engines are highly developed very high speed units where the actual size of the ports has become a restriction. Often the size of the port is reduced to increase power. A mirror finish of the port does not provide the increase that intuition would suggest. In fact, within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the boundary layer, which can alter the flow path noticeably, possibly increasing flow. This is similar to what the dimples on a golf ball do. Flow bench testing shows that the difference between a mirror finished intake port and a rough textured port is typically less than 1%. The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means. Exhaust ports may be smooth finished because of the dry gas flow and in the interest of minimizing exhaust by-product build-up. A 300 - 400 Grit finish followed by a light buff is generally accepted to be representative of a near optimal finish for exhaust gas ports.
The reason that polished ports are not advantageous from a flow standpoint is that at the interface between the metal wall and the air, the air speed is ZERO (see boundary layer and laminar flow). This is due to the wetting action of the air and indeed all fluids. The first layer of molecules adheres to the wall and does not move significantly. The rest of the flow field must shear past which develops a velocity profile (or gradient) across the duct. In order for surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center.
It is popularly held that enlarging the ports to the maximum possible size and applying a mirror finish is what porting is. However that is not so. Some ports may be enlarged to their maximum possible size (in keeping with the highest level of aerodynamic efficiency) but those engines are highly developed very high speed units where the actual size of the ports has become a restriction. Often the size of the port is reduced to increase power. A mirror finish of the port does not provide the increase that intuition would suggest. In fact, within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the boundary layer, which can alter the flow path noticeably, possibly increasing flow. This is similar to what the dimples on a golf ball do. Flow bench testing shows that the difference between a mirror finished intake port and a rough textured port is typically less than 1%. The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means. Exhaust ports may be smooth finished because of the dry gas flow and in the interest of minimizing exhaust by-product build-up. A 300 - 400 Grit finish followed by a light buff is generally accepted to be representative of a near optimal finish for exhaust gas ports.
The reason that polished ports are not advantageous from a flow standpoint is that at the interface between the metal wall and the air, the air speed is ZERO (see boundary layer and laminar flow). This is due to the wetting action of the air and indeed all fluids. The first layer of molecules adheres to the wall and does not move significantly. The rest of the flow field must shear past which develops a velocity profile (or gradient) across the duct. In order for surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center.
Discuss!
10-27-2008, 10:14 PM
#2
Senior Member
Join Date: 10-06-05
Location: Seneca, South Carolina
Posts: 10,944
Likes: 0
Received 2 Likes
on
2 Posts
My opinion from the other thread.
I'm a little confused by your statements Omega. First off, I though ported head did give "insane" numbers. Or is Rebel Auto Worx an idiot company that should just quit.
Also, I thought you didn't polish the bottom side of the INTAKE ports on a head because it would effect the fuel spray from the injectors. At least that's what I was taught. I know tons of people that port and polish tb's, intake manifolds, and heads and air moves through all of that.
I'm a little confused by your statements Omega. First off, I though ported head did give "insane" numbers. Or is Rebel Auto Worx an idiot company that should just quit.
Also, I thought you didn't polish the bottom side of the INTAKE ports on a head because it would effect the fuel spray from the injectors. At least that's what I was taught. I know tons of people that port and polish tb's, intake manifolds, and heads and air moves through all of that.
10-27-2008, 10:16 PM
#3
Senior Member
Join Date: 10-13-08
Location: Georgia
Posts: 1,198
Likes: 0
Received 0 Likes
on
0 Posts
this is a very dumb post.
polishing increases CFM due to lack of "friction". True the first layer is "stuck" in place but that is a layer better used going along it's path. Saying friction doesnt expand oxygen atoms is silly and has been proven scientifically to "excite" atoms increasing "said" volume thus less oxygen to the chamber.
Take an airplane for instance... if this were to hold true we would have bumpy airplanes so that air could "glide" better on the surface. whoever made that wiki should be shot.
Please show me his post that the world is flat, and that we should prove it isnt?
polishing increases CFM due to lack of "friction". True the first layer is "stuck" in place but that is a layer better used going along it's path. Saying friction doesnt expand oxygen atoms is silly and has been proven scientifically to "excite" atoms increasing "said" volume thus less oxygen to the chamber.
Take an airplane for instance... if this were to hold true we would have bumpy airplanes so that air could "glide" better on the surface. whoever made that wiki should be shot.
Please show me his post that the world is flat, and that we should prove it isnt?
10-27-2008, 10:23 PM
#6
Senior Member
Join Date: 10-13-08
Location: Georgia
Posts: 1,198
Likes: 0
Received 0 Likes
on
0 Posts
10-27-2008, 10:27 PM
#8
Senior Member
Join Date: 10-13-08
Location: Georgia
Posts: 1,198
Likes: 0
Received 0 Likes
on
0 Posts
Do whatever you want with your car.
10-27-2008, 10:42 PM
#9
Senior Member
Join Date: 10-06-05
Location: Seneca, South Carolina
Posts: 10,944
Likes: 0
Received 2 Likes
on
2 Posts
I'm paying a professional to CNC mine when I get the money anyways, So I'm not worried about it. But this is still good info and a good thread for a discussion.
10-27-2008, 11:13 PM
#10
Senior Member
Join Date: 06-11-07
Location: Minnesota
Posts: 885
Likes: 0
Received 0 Likes
on
0 Posts
Okay lets go back to basics..
Talk to the professionals, these guys have porting down and even help you do it. READ their how-to
Basic Port job
smooth Intake ports to 80 grit, DO NOT POLISH. Why? because intake air needs to swirl, it helps cylinder filling, fuel atomization and which means better more efficient combustion.
More efficient combustion=more power
headwork is not only about getting more air into the combustion chambers, you can push all the air you want into the cylinder if the fuel molecules "fall" out of the air (think condensation) they will not burn as easily making less power than before, more carbon build up yadda yadda yadda..
LSJ rely on efficiencies... you get out the efficiency range on ANYTHING and your hurting more than helping. spinning a 2.8 pulley with a stock head/exhaust and intake manifold, yes will make more hp over stock, but at the cost of more heat and more fuel to keep combustion temps and ignition timing under control. harder on the injectors/pump
you start pushing anything to its limits and somethings got to give, there is a reason why so many of these cars blow up daily.
Talk to the professionals, these guys have porting down and even help you do it. READ their how-to
Basic Port job
smooth Intake ports to 80 grit, DO NOT POLISH. Why? because intake air needs to swirl, it helps cylinder filling, fuel atomization and which means better more efficient combustion.
More efficient combustion=more power
headwork is not only about getting more air into the combustion chambers, you can push all the air you want into the cylinder if the fuel molecules "fall" out of the air (think condensation) they will not burn as easily making less power than before, more carbon build up yadda yadda yadda..
LSJ rely on efficiencies... you get out the efficiency range on ANYTHING and your hurting more than helping. spinning a 2.8 pulley with a stock head/exhaust and intake manifold, yes will make more hp over stock, but at the cost of more heat and more fuel to keep combustion temps and ignition timing under control. harder on the injectors/pump
you start pushing anything to its limits and somethings got to give, there is a reason why so many of these cars blow up daily.
10-27-2008, 11:33 PM
#11
Senior Member
Join Date: 10-13-08
Location: Georgia
Posts: 1,198
Likes: 0
Received 0 Likes
on
0 Posts
Okay lets go back to basics..
Talk to the professionals, these guys have porting down and even help you do it. READ their how-to
Basic Port job
smooth Intake ports to 80 grit, DO NOT POLISH. Why? because intake air needs to swirl, it helps cylinder filling, fuel atomization and which means better more efficient combustion.
More efficient combustion=more power
headwork is not only about getting more air into the combustion chambers, you can push all the air you want into the cylinder if the fuel molecules "fall" out of the air (think condensation) they will not burn as easily making less power than before, more carbon build up yadda yadda yadda..
LSJ rely on efficiencies... you get out the efficiency range on ANYTHING and your hurting more than helping. spinning a 2.8 pulley with a stock head/exhaust and intake manifold, yes will make more hp over stock, but at the cost of more heat and more fuel to keep combustion temps and ignition timing under control. harder on the injectors/pump
you start pushing anything to its limits and somethings got to give, there is a reason why so many of these cars blow up daily.
Talk to the professionals, these guys have porting down and even help you do it. READ their how-to
Basic Port job
smooth Intake ports to 80 grit, DO NOT POLISH. Why? because intake air needs to swirl, it helps cylinder filling, fuel atomization and which means better more efficient combustion.
More efficient combustion=more power
headwork is not only about getting more air into the combustion chambers, you can push all the air you want into the cylinder if the fuel molecules "fall" out of the air (think condensation) they will not burn as easily making less power than before, more carbon build up yadda yadda yadda..
LSJ rely on efficiencies... you get out the efficiency range on ANYTHING and your hurting more than helping. spinning a 2.8 pulley with a stock head/exhaust and intake manifold, yes will make more hp over stock, but at the cost of more heat and more fuel to keep combustion temps and ignition timing under control. harder on the injectors/pump
you start pushing anything to its limits and somethings got to give, there is a reason why so many of these cars blow up daily.
please fail elsewhere.
10-27-2008, 11:45 PM
#13
Senior Member
Join Date: 10-13-08
Location: Georgia
Posts: 1,198
Likes: 0
Received 0 Likes
on
0 Posts
Exhaust has ALOT to do with it
10-27-2008, 11:46 PM
#15
Banned
Join Date: 11-23-06
Location: south of Pittsburgh, Pennsylvania
Posts: 3,182
Likes: 0
Received 0 Likes
on
0 Posts
That read-up up also doesn't point out the fact that "polishing" the intake side can be a bad thing because a finish to smooth can hinder fuel atomization.
10-27-2008, 11:48 PM
#16
Senior Member
Join Date: 10-06-05
Location: Seneca, South Carolina
Posts: 10,944
Likes: 0
Received 2 Likes
on
2 Posts
Last edited by ralliartist; 10-27-2008 at 11:48 PM. Reason: Automerged Doublepost
10-27-2008, 11:51 PM
#17
Senior Member
Join Date: 10-13-08
Location: Georgia
Posts: 1,198
Likes: 0
Received 0 Likes
on
0 Posts
10-27-2008, 11:51 PM
#18
Banned
Join Date: 11-23-06
Location: south of Pittsburgh, Pennsylvania
Posts: 3,182
Likes: 0
Received 0 Likes
on
0 Posts
Same thing i was taught. Leave a 220-300 grit finish on the intake side and polish the exhaust side.
10-27-2008, 11:57 PM
#19
Senior Member
Join Date: 06-11-07
Location: Minnesota
Posts: 885
Likes: 0
Received 0 Likes
on
0 Posts
I never said anything about you or your car in that thread, everything I posted is facts
what your car did, doesn't really matter to me.. i don't see how I "failed"
10-28-2008, 12:02 AM
#20
Senior Member
iTrader: (3)
Join Date: 03-27-08
Location: Linden, New Jersey
Posts: 1,918
Likes: 0
Received 0 Likes
on
0 Posts
10-28-2008, 12:03 AM
#21
Senior Member
Join Date: 10-13-08
Location: Georgia
Posts: 1,198
Likes: 0
Received 0 Likes
on
0 Posts
WOW..............
WOW!!!!!!!!!!!!!!!! LOL you must be bored.
props and +1 invis rep
10-28-2008, 10:06 AM
#22
Senior Member
Thread Starter
Join Date: 10-01-06
Location: Maidstone, SK
Posts: 5,134
Likes: 0
Received 0 Likes
on
0 Posts
I figured this was how this thread would play out.
I love how people compare to airplane wings, but not to golf *****.
And airplane wing is a surface pressure differential, as opposed to a simple flow... it is affected by a different phenomenon called skin friction drag.
Therefore that idea is out the window.
However... in some cases... we do see certain devices on airplanes which does take the 'dimple' principle into affect... look up 'votrex generators' or leading edge extensions.
Anyways... we're not talking about planes here though...
I won't bother wasting my time on the technical details behind it... but I dare any nay-sayers to go over to an SBC or Honda forum and tell them that polished ports are the ****... they'll laugh you out of there to fast.
And Ralli... no, I have not put my head on the car... but the flow bench test were promising.
Raptors... look at this link... the dimples in a golf ball are for distance, not spin.
http://www.howstuffworks.com/question37.htm
I love how people compare to airplane wings, but not to golf *****.
And airplane wing is a surface pressure differential, as opposed to a simple flow... it is affected by a different phenomenon called skin friction drag.
The reason we do not see dimples on other shapes, like wings, is that these particular forms of boundary layer trips only work well on a blunt body like a sphere or a cylinder. The most dominant form of drag on these kinds of shapes is caused by pressure, as we have seen throughout this discussion. More streamlined shapes like the airfoils used on wings are dominated by a different kind of drag called skin friction drag. These streamlined bodies, like that pictured above, have a teardrop shape that creates a much more gradual adverse pressure gradient. This less severe gradient promotes attached flow much further along the body that eliminates flow separation, or at least delays it until very near the trailing edge. The resulting wake is therefore very small and generates very little pressure drag.
However... in some cases... we do see certain devices on airplanes which does take the 'dimple' principle into affect... look up 'votrex generators' or leading edge extensions.
Anyways... we're not talking about planes here though...
I won't bother wasting my time on the technical details behind it... but I dare any nay-sayers to go over to an SBC or Honda forum and tell them that polished ports are the ****... they'll laugh you out of there to fast.
And Ralli... no, I have not put my head on the car... but the flow bench test were promising.
Raptors... look at this link... the dimples in a golf ball are for distance, not spin.
http://www.howstuffworks.com/question37.htm
If you want to get deeper into the aerodynamics, there are two types of flow around an object: laminar and turbulent. Laminar flow has less drag, but it is also prone to a phenomenon called "separation." Once separation of a laminar boundary layer occurs, drag rises dramatically because of eddies that form in the gap. Turbulent flow has more drag initially but also better adhesion, and therefore is less prone to separation. Therefore, if the shape of an object is such that separation occurs easily, it is better to turbulate the boundary layer (at the slight cost of increased drag) in order to increase adhesion and reduce eddies (which means a significant reduction in drag). Dimples on golf ***** turbulate the boundary layer.
Last edited by Omega_5; 10-28-2008 at 10:37 AM.
10-28-2008, 11:08 AM
#23
Senior Member
Join Date: 10-13-08
Location: Georgia
Posts: 1,198
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by PhantomSS
this is 6 tenths of one half a dozen the other.
Anyway there is always a tradeoff.
10-29-2008, 01:04 AM
#24
Senior Member
Join Date: 02-06-05
Location: sk
Posts: 645
Likes: 0
Received 0 Likes
on
0 Posts
I figured this was how this thread would play out.
I love how people compare to airplane wings, but not to golf *****.
And airplane wing is a surface pressure differential, as opposed to a simple flow... it is affected by a different phenomenon called skin friction drag.
Therefore that idea is out the window.
However... in some cases... we do see certain devices on airplanes which does take the 'dimple' principle into affect... look up 'votrex generators' or leading edge extensions.
Anyways... we're not talking about planes here though...
I won't bother wasting my time on the technical details behind it... but I dare any nay-sayers to go over to an SBC or Honda forum and tell them that polished ports are the ****... they'll laugh you out of there to fast.
And Ralli... no, I have not put my head on the car... but the flow bench test were promising.
Raptors... look at this link... the dimples in a golf ball are for distance, not spin.
http://www.howstuffworks.com/question37.htm
I love how people compare to airplane wings, but not to golf *****.
And airplane wing is a surface pressure differential, as opposed to a simple flow... it is affected by a different phenomenon called skin friction drag.
Therefore that idea is out the window.
However... in some cases... we do see certain devices on airplanes which does take the 'dimple' principle into affect... look up 'votrex generators' or leading edge extensions.
Anyways... we're not talking about planes here though...
I won't bother wasting my time on the technical details behind it... but I dare any nay-sayers to go over to an SBC or Honda forum and tell them that polished ports are the ****... they'll laugh you out of there to fast.
And Ralli... no, I have not put my head on the car... but the flow bench test were promising.
Raptors... look at this link... the dimples in a golf ball are for distance, not spin.
http://www.howstuffworks.com/question37.htm
I thought i said they affected distance? And I know they affect spin and trajectory as I've seen tests done on different types of *****. Good read though!
