I'm not sure I understand your logic. Are you saying that the heat transferred from the intake manifold to the air goes into the cylinders and reduces HP? Power is lost because the heat transfered to the air decreases the density of the air = less fuel burned, not because "of heat going back into the engine".

 

I always thought that was due to the sanding materials they use.

 

It is but they could polish it like a mirror or a set of wheels to be like chrome. That was done back that way in the '60's until it was found out that a rougher surface would make more HP.

 

I have heard the same thing. It was explained to me that a slightly rougher surface produces a slight amount of turbulence which in turn helps to atomize the fuel a little better.

 

Correct
It strengthens the boundary layer and helps with fuel separation.

 

That doesn't mean that a smooth surface won't flow better, just that a rough surface will keep fuel in suspension better. That would suggest that if you could wet flow test the intake side of an engine you’d probably find that you only needed rough surfaces in a few areas, and almost nowhere in an FI setup.

 

NOT correct.

 

Agreed.

In a FI car it will push harder against the walls meaning it might want to smooth out more. Just because air is moving faster with more pressure does not mean it will keep the fuel atomized. If anything I would think it will work the other way. Kind of like compressing air in a tank, and you get water droplets. Just my logic, I could be wrong though.

About the intake manifold, I think keeping it cooler would help, but not because energy is being lost into the manifold. It would just help keep the air a little denser until it reached the cylinder.

 

In this case we are talking about a fuel injection system. So there will only be air and no air/fuel mixture until we reach the heads. So the runners in the heads should remain unpolished to help the fuel suspension. IMHO anything upstream of the heads would help the airflow if it was smooth such as using the Teflon coating.

Couple of thoughts. If the Teflon coating increased the intake air flow by 5 cfm that would be equal to around 10 horsepower. If the Teflon coating turned out to be a good themal barrier that could very well be worth another 10 horsepower. I believe both scenarios are entirely possible so I will have to give it a try.

From my reasearch I have found that teflon PFA as a thermal conductivity of .19 w/mk. If anyone on the forum can shed some light on that number I would appreciate it. Thanks

 

my head hurts.

 

According to what I found on the internet that number means the "thermal admittance". For every one degree in temperature change on one side, the other side will see .19 degree change. Hopefully I interpretted wikipedia right.

 

mirror finish is going to have better airflow characteristics near the walls, less turbulence, higher flux, less area and less heat transfer.

yes most prefer semi smooth because this will aid in mixing the air fuel mixture completely, however if you are looking at cfm alone smooth will do it.

if you account for the fact that extra mixing helps, well, then you're adding in an interesting variable, because at high rpm, the mixture near the walls won't move near as fast as the mixture in the center due to the turbulence along the walls. But when the mixture is moving slower, this turbulence will keep it mixed better until it enters the cylinder, which is an issue as the fuel particles will 'fall out' of solution with the air. So what you need is what you need.

EDIT: w/mk is watts per meter kelvin, and the equations involve area and thickness of material, basically the constant (.19) gets entered into an equation that incorporates the area of material and the thickness, then your time factor gets calculated and you get your change in temperature on the other side

 

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 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 but an optical finish is wasted effort and money.

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. 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. Only a very rough surface does this.




A common beginning porter’s mistake is to apply a nice, shiny finish to all ported surfaces. If your heads come back this way from a tuner, expect less, not more power!

 

Thanks guys for all the input. Here is something for comparison. 6061 aluminum has a thermal conductivity of 171 W/mk. The PFA Teflon has a .19 W/mk. So the Teflon is 900 times a better thermal barrier than the aluminum. I think that gives me the information I need. Teflon here I come. Still open to opinions.

 

Some more on how to do it.


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Coating an Intake Manifold

There are two reasons for coating an intake manifold. The first would be Performance, the second Appearance. Let's discuss Performance first.

In this instance, you are dealing with heat that is generated by the engine. You will also acquire heat from the hot oil that may be tossed up under the underside of the intake manifold. This means we want to apply a thermal barrier ( TLLB, CBC2, CBX, MCX ) to the bottom of the intake manifold, the flange area where it would bolt to the head and also the flange area where the carburetor would bolt to the intake manifold. This will reduce the amount of heat that enters the manifold itself, keeping the manifold cooler. Typically, a normally aspirated engine will see a 1% improvement in power for every 10 degree drop in carb air inlet temperature. A Turbo charged engine will see a 2% increase. Keeping the manifold cooler than normal allows an engine to generate more horse power. In addition to this, you would coat the top of the manifold with a thermal dispersant such as our TLTD. This means that the heat that does get into the intake manifold will be more rapidly dispersed into the air moving over it, thus cooling the intake manifold further. This gives you a greater chance of creating more horse power by reducing the inlet temperature. You can also coat the inside of the runners in an intake manifold. You can use 1 or 2 coatings. A single coating that we recommend would be our dry film ( DFL-1, TLML or CERMA LUBE ). These are known as 'fluid retaining coatings' and the fuel/air mix as it passes through an intake manifold on a carbureted engine is treated like a 'fluid in motion'. The coating will have a tendency to create a small amount of boundary layer turbulence which will reduce fuel drop-out. You may also apply a thermal barrier to the inside of a runner first, then the dry film over it. If you're doing this, we recommend using our TLLB with TLML over the top of it. You not only create the boundary layer turbulence, you further reduce the amount of heat that does enter the fuel/air mix.

On the cosmetic side, while the TLTD is a very nice-looking coating, it is Black. If someone is looking for more show and they like a bright, polished appearance, then Cermakrome, as an example, can be used. Since Cermakrome is a thermal barrier, we recommend that you coat the bottom and the top. In this way, while you're inhibiting the amount of heat that can be dispersed from the top of the manifold because of it being coated, you're reducing the amount of heat that can be absorbed by the manifold because of the same coating on the bottom. Thus, you are at least creating an equilibrium and not dealing with a heat problem. The coating is extremely high temperature resistant, does not blue or discolor like chrome, does not oxidize significantly as a polished aluminized surface will, so you can maintain a very nice, high-polished surface not affected by fuel oils and solvents.