I was discussing intake manifold material on another forum, and wondered what you guys thought. I feel aluminum is the superior material then stainless steel for an intake manifold not only because of its light weight, but its high thermal transfer rate. What do you think?


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by "Justin Olson" &raquo;</TD></TR><TR><TD CLASS="quote">Stainless dissipates heat much slower then aluminum, so you end up with a higher temperature intake charge.</TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by "Jorgen" &raquo;</TD></TR><TR><TD CLASS="quote">
I can't agree, from a thermal standpoint stainless is very good, it transport heat slowly. That means that less of the stainless manifold will be heated by the cylinder head when for example in the lineup or in slow city traffic.

The lower heat radiation of it will make it take up less heat from the engine bay and will minimize the heat transfer to the charge air.

I'm not sure if this will add power but it definitely makes it possible to have a better IAT sensor placement on a speed-density mapped car.

The different properties of stainless makes it more prone to cracking, mostly because the higher weight of the material force the use of thin sheet metal and because people tend to grind most the welds away before they polish the intake. Remember that the forces that act on the intake manifold is pretty high and that the intake manifold see pretty strong pulses.

Jörgen</TD></TR></TABLE>

 

composites or certain plastics are best... aluminum does heat up too quickly.

 

Physical Data : AA 6061

Density (×1000 kg/m3) 2.7
Poisson's Ratio 0.33
Elastic Modulus (GPa) 70-80
Tensile Strength (Mpa) 115
Yield Strength (Mpa) 48
Elongation (%) 25
Reduction in Area (%)
Hardness (HB500) 30
Shear Strength (MPa) 83
Fatigue Strength (MPa) 62
Thermal Expansion (10-6/ºC) 23.4
Thermal Conductivity (W/m-K) 180
Specific Heat (J/kg-ºK) "The specific heat of 6061 Al varies significantly over this temperature range (from about 200 J/kg/K at 60K to about 870 J/kg/K at 293K); a reasonable rough average is 650 J/kg/K."


Physical Data : AISI Type 304

Density (×1000 kg/m3) 8
Poisson's Ratio 0.27-0.30
Elastic Modulus (GPa) 193
Tensile Strength (Mpa) 515
Yield Strength (Mpa) 205
Elongation (%) 40
Reduction in Area (%) 50
Hardness (HRB) 88 25
Thermal Expansion (10-6/ºC) 17.2
Thermal Conductivity (W/m-K) 16.2
Specific Heat (J/kg-ºK) 500

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by "Wikipedia.org" &raquo;</TD></TR><TR><TD CLASS="quote">Specific heat capacity, also known simply as specific heat (Symbol: C or c) is the measure of the heat energy required to raise the temperature of a specific quantity of a substance (thus, the name “specific” heat) by certain amount, usually one kelvin. A kelvin is a unit increment of thermodynamic temperature and is precisely equal to an increment of one degree Celsius. Virtually any substance may have its specific heat capacity measured, including pure chemical elements, compounds, alloys, solutions, and composites.</TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by "Wikipedia.org" &raquo;</TD></TR><TR><TD CLASS="quote">In physics, thermal conductivity, k, is the intensive property of a material that indicates its ability to conduct heat.

It is defined as the quantity of heat, Q, transmitted in time t through a thickness L, in a direction normal to a surface of area A, due to a temperature difference ΔT, under steady state conditions and when the heat transfer is dependent only on the temperature gradient.

thermal conductivity = heat flow rate × distance / (area × temperature difference)
</TD></TR></TABLE>



Modified by Justin Olson at 10:58 AM 7/24/2006

 

right. thats saying ss conducts less heat.

also i dont know if it was their mistake, but the units of sp. ht. are different for both.

-derek

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by "Wikipedia.org" &raquo;</TD></TR><TR><TD CLASS="quote">Heat transfer mechanisms

As mentioned previously, heat tends to move from a high temperature region to a low temperature region. This heat transfer may occur by the mechanisms conduction and radiation. In engineering, the term convective heat transfer is used to describe the combined effects of conduction and fluid flow and is regarded as a third mechanism of heat transfer.


Conduction

Conduction is the most common means of heat transfer in a solid. On a microscopic scale, conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring atoms. In insulators the heat flux is carried almost entirely by phonon vibrations.

The "electron fluid" of a conductive metallic solid conducts nearly all of the heat flux through the solid. Phonon flux is still present, but carries less than 1% of the energy. Electrons also conduct electric current through conductive solids, and the thermal and electrical conductivities of most metals have about the same ratio. A good electrical conductor, such as copper, usually also conducts heat well. The Peltier-Seebeck effect exhibits the propensity of electrons to conduct heat through an electrically conductive solid. Thermoelectricity is caused by the relationship between electrons, heat fluxes and electrical currents.


Convection

Convection is usually the dominant form of heat transfer in liquids and gases. This is a term used to characterize the combined effects of conduction and fluid flow. In convection, enthalpy transfer occurs by the movement of hot or cold portions of the fluid together with heat transfer by conduction. For example, when water is heated on a stove, hot water from the bottom of the pan rises, heating the water at the top of the pan. Two types of convection are commonly distinguished, free convection, in which gravity and buoyancy forces drive the fluid movement, and forced convection, where a fan, stirrer, or other means is used to move the fluid. Buoyant convection is due to the effects of gravity, and hence does not occur in microgravity environments.


Radiation

Radiation is the only form of heat transfer that can occur in the absence of any form of medium and as such is the only means of heat transfer through a vacuum. Thermal radiation is a direct result of the movements of atoms and molecules in a material. Since these atoms and molecules are composed of charged particles (protons and electrons), their movements result in the emission of electromagnetic radiation, which carries energy away from the surface. At the same time, the surface is constantly bombarded by radiation from the surroundings, resulting in the transfer of energy to the surface. Since the amount of emitted radiation increases with increasing temperature, a net transfer of energy from higher temperatures to lower temperatures results.

For room temperature objects (~300 K), the majority of photons emitted (and involved in radiative heat transfer) are in the infrared spectrum, but this is by no means the only frequency range involved in radiation. The frequencies emitted are partially related to black-body radiation. Hotter objects—a light bulb filament at 3000K for instance—transfer heat in the visible spectrum or beyond. Whenever EM radiation is emitted and then absorbed, heat is transferred. This principle is used in microwave ovens, laser cutting, and RF hair removal.</TD></TR></TABLE>

 

So from my view you have to identify the heat sources and sinks in the engine bay to properly figure out what material will best suit the needs of an intake manifold.

Sources:
Cylinder Head
Intake air charge

Sink:
Ambient Airflow through the engine bay

It seems to me with proper venting of the engine bay, ambient airflow will be high enough to keep the intake manifold cooler then the incoming air charge. If the ambient air in the engine bay is sufficent, the intake manifold will be cooler then the intake air charge. The intake air charge will be cooled as it passes through the intake manifold in this case.

If there isn't sufficient airflow around the intake manifold, its temperature will be higher then the intake air charge. The intake air charge will be heated as it passes through the intake manifold in this case.

 

you probably wont ever get the intake manifold to be lower temp than the air, lol.
due to conduction.

 

This is a tricky subject.

Aluminum will suck up the heat from the head the best. It will also shed the heat to the air the best. The con is, it will also transfer heat to the intake stream the easiest and if the engine bay does not get good air circulation, will result in the intake becoming heatsoaked extremely easily.

Stainless steel will suck up the head from the head pretty poorly. It will also shed the heat to the air pretty poorly as well. The pro is, since it doesn't really transfer that much heat, it won't heat up intake temps as easily. If you infact get poor air circulation in the engine bay, you don't have to worry as much since the stainless manifold won't be transfering as much heat as aluminum.

Overall, which one is best? ****, I don't know. I think it depends on the variables I mentioned above. I think I would use some thick aluminum.

 

What about mild steel?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dfoxengr &raquo;</TD></TR><TR><TD CLASS="quote">you probably wont ever get the intake manifold to be lower temp than the air, lol.
due to conduction.</TD></TR></TABLE>

Alot of the air comes into the engine bay has all ready ran through the radiator and an intercooler if you have one. Plus if the intake manifold is out back, then the air had to go around the very hot engine first before it got to the intake manifold.

So the point is, the air thats cooling off the intake manifold is going to get heated on its way in anyways. Where as the ambient air (in a naturally aspirated motor) comes from the outside and then only has to travel through the intake piping. Now a turbo could heat up the air very easily to beyond the temps of the intake manifold.

Those teflon manifold gaskets could help minimize the heat transfer from the head.

 

I wanna revitalize this thread. I think this was a good topic that ended too soon. This is an issue I've been researching, and I think there are alot of argueable points brought up that weren't really addressed.

I've often argued stainless steels low conduction properties as a plus for induction components, especially if barrier coatings/thermal gaskets are applied to insulate it from engine bay temperatures and head contact surface.

Anyone want to throw in some opinions?

 

I believe that theory and metallurgy are a good starting point for an answer, but it doesn't cover everything. What about the "life" of the intake manifold? Car starts, warms up, intake manifold warms up, one simply gets hotter faster, the other stays hotter longer. Car sees boost, car sees normal grandma driving. Now which one is better?

I think Mild steel was an awesome answer, but it would fail on the fact that it is prone to corrosion. I personally want to try a shot at a stainless mani with ceramic coating.

Thoughts?

 

Well, another part to consider is the workability of the two materials for an intake application. Aluminum is much easier to work with, especially if your going for complex plenum shaping. It's also alot easier to cut.

Stainless, on the other hand, requires alot less of a machine to weld, and will result in a very attractive end unit.

There are certainly a ton of variables. I think the OEM's have been attracted to aluminum for some time just because, in terms of production, cast units are easy to produce. They certainly aren't gonna go cast iron, or cast stainless, so cast aluminum is a clear winner there. Now with plastics becoming more popular, that's going to become very popular....arguably it already has.

 

How about a phenolic spacer between the manifold and the head. Then you could run a stainless inlet manifold and not worry about it heating up from the head.

Justin

 

good ideas guys...keep that brain kickin!

also I never pulled out the IR temp meter on the intake mani but when i propped my hood open using the washer trick...i notice a slight decrease in iat's...whether or not that is subjectable to the hood change is minimal but my intake mani felt a whole lot colder after hard boosted runs...as the air is being drawn in behind the hood and running down behind the motor and out the bottom of the bay

 

i'm suprised it hasn't been mentioned earlier in this thread... what about thermal cycling? i can't see a ss manifold cooling down quicker than an aluminum one since it doesn't transfer temperature change well. so once up to regular engine operating temp, wouldn't the ss mani hold that heat for a longer period of time? i'd think this would be something to avoid.

another question is: are any oem's running ss intake components? i don't know of any off hand. there must be a reason for this besides cost. we are starting to see more and more of the composite/plastic intake manifolds as well.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DESTROYER &raquo;</TD></TR><TR><TD CLASS="quote">What about the "life" of the intake manifold? Car starts, warms up, intake manifold warms up, one simply gets hotter faster, the other stays hotter longer. Car sees boost, car sees normal grandma driving. Now which one is better?
</TD></TR></TABLE>
This is when I was referring to cycling. The stainless sure would have issues there, however with using a non heat conductive material to seperate it from the head, along with ceramic coating inside and out... you then MIGHT have an efficient setup, but it loses efficiency on the $ value, because it will cost over $2k to build it. Heat soak is an issue, so stainless goes pretty much out the window.

Now, what about a water cooled aluminum intake manifold?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DESTROYER &raquo;</TD></TR><TR><TD CLASS="quote">
Now, what about a water cooled aluminum intake manifold?
</TD></TR></TABLE>

there is something i have thought of in the past. i don't think it would be practical for daily use, but could be very effective at the track if it was built properly.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by weiRtech &raquo;</TD></TR><TR><TD CLASS="quote">another question is: are any oem's running ss intake components? i don't know of any off hand. there must be a reason for this besides cost. we are starting to see more and more of the composite/plastic intake manifolds as well.</TD></TR></TABLE>


It is all cost Aaron. Aluminum was chosen for cost, but lacked the thermal properties needed for cooler IATs.

SS is a better choice by far, but the cost factor deterred them, so they waited for somethign better. Plastic is 10x better in terms of thermal conductivity and specific heat than even SS, and has become extremely cheap to mold, produce, etc, thus the switch.

The best material thermal wise is an insulator. The intake air will always start out cooler than the engine or anything else in the bay. The key idea is to avoid heat transfer from the intake pipe and intake manifold, basically anything that comes into contact with the air.

Aluminum is a horrible material for this use. It transfers heat fast and in large quantities. A poor choice.

Hondata nailed it right on the head with the intake manifold gasket that acts as a thermal barrier.

One thing to remember about heat transfer is that it will happen eventually. The idea is to slow it down as much as possible and that means a material that has a super low thermal conductivity. Plastics are great at this.

 

I would have to agree that the rate of transfer is important, but you have to consider the fact the the stainless one will get hotter than the aluminum one over time. If weare talking a drag car, strictly race, then I can see the benefit.
If we are talking road racer,rally, or even daily, the stainless maifold would get hotter by a fair margin based on time.

The most cost and heat-efficient I think would be coated mild steel.
1/2 the warpage, 1/2 the cost, and you will coat it anyway, so corrosion isn't a factor.

Plastic would easily be the best, but finding a material that can take the heat, and can be machined/formed,etc. is not that easy.

 

I think this could be a truly workable approach. The mild steel makes fab a little harder, but if you get past that, and get the unit coated inside and out by a company like HPC, you could have a descent piece.

 

so who is going to build the first phenolic manifold? or has it been done already?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by weiRtech &raquo;</TD></TR><TR><TD CLASS="quote">so who is going to build the first phenolic manifold? or has it been done already?</TD></TR></TABLE>


Oh man, can you imagine a manifold made out of bakelite. HAHAHA.

 

I am having a hard time understanding why a Stainless Manifold will get hotter in use. The thermal conductivity works both ways, it takes longer to cool down but at the same time it takes longer to heat up. I have a feeling manufacturers went with aluminum because it was lighter and didn't cost to much. Back in the day they made cast iron manifolds and im sure they changed over to aluminum for a reason.

Like some people have said a composite manifold would be optimal, for weight and thermal conductivity reasons.

Bakelite..........haha i would not want to be around it the first time somone did a dyno run under some decent boost. Can you imagine the shrapnel?

 

I'm working on making a carbon manifold for an EJ25.... we have literally TONS of carbon and resin