[AMG Aper]

Hi everyone!

I've been wanting to do this post for a while now, and I finally got around to getting it written up. I would love and appreciate ANY changes or feedback or additions to better-improve this post for future viewers, especially by those with hands-on experience in thermodynamics or even building and testing intakes / exhaust and other components!

This is going to be a LONG discussion about the physics of heat transfer, & my experience designing 2 versions of a custom intake for my 2007 SLK55.

When I was looking at the intake of my R171 SLK55 AMG with the lovely M113 engine, it seemed that the stock design was pretty good right out of the factory, however I am always one to tinker for a better solution. I wanted to experiment with ways to improve our intake’s flow characteristics and reduce intake air temperatures, as we will see cramming a large V8 in such a small space makes this experiment much more important.

In this experiment, my aim was to reduce intake air temperatures mainly, but due to the better-flowing design of my 2 intake designs, the overall air flow was greatly improved as well.

NOTE: All of these observations during stock, design #1, and design #2, are after installing my TrackSpec Hood Louvers (picture in next post, didn't have room here), which allow the hot high pressure air under the hood to naturally escape over the top, thereby allowing the radiator to channel more colder ambient air through its coils.

Thermodynamics & Heat Transfer​

Before I show you the 1st and 2nd prototypes I made, I think it’s very important to have an overall discussion of what “heat” is in terms of thermodynamics, and how a better understanding of this concept will truly help us design a much more efficient intake. (Note, if you want to skip the entire thermodynamics discussion, feel free, but you might learn a thing or two!)

Class is now in session!​

Heat is thermal energy that is always transferred from matter that is hotter to matter that is cooler in temperature. This heat transfer can be categorized by three different methods, of which all three methods are occurring underneath our hoods:

• Conduction (Cd)
• Convection (Cv)
• Radiation (Ra)

(credit: Mrs. Yunker, Quizizz, Quizizz — The world’s most engaging learning platform)

In the simplest of terms, conduction is the transfer of heat between a solid to another solid by direct contact, such as two objects directly touching each other and having the hotter object transfer part of its heat to the colder object.

Convection is when there is a “fluid” transferring heat to and between another fluid or a solid object, such as our coolant or oil absorbing the heat from the metal pipes and engine components it circulates through, or when you “feel” the hot air from a hair dryer blowing against your face or hands (air is considered a “fluid” in terms of its flow characteristics).

Radiation deals with the properties of “thermal radiation”, which is the “invisible” light waves that comprise heat energy (such as the heat we feel from popping our hoods after a long drive, the warmth of the sun, or standing close to a hot object and feeling its heat without actually touching the object.)

(credit: The Efficient Engineer,

)

It is important to note, that Radiation is also divided into 3 separate subcategories of interaction, whereby the thermal radiation “interacts” with other objects. This interaction is called “irradiation,” or the radiation “received” by an object.

In a nutshell, there are actually 3 main process and 3 sub-processes of heat transfer going on under our hoods at the same time!

1. Conduction
2. Convection
3. Radiation (waves radiating from a surface) to Irradiation (waves meeting a surface)
   • Reflection
   • Transmission
   • Absorption

Conduction & Convection​

(credit: Cradle CFD Software, Cradle CFD | Smart Multiphysics Focused CFD simulation | Hexagon)

(credit: Free Pik, Free Vector | Diagram showing the convection process">Image by brgfx</a> on Freepik)

The most important characteristic of conduction (Cd) and convection (Cv) we want to analyze & understand is called Thermal Conductivity (k), in the unit of W/(m*K) (which is Watts over meters times Kelvin).

Thermal conductivity is a constant that represents a unique value for different types of materials, and it represents how much heat energy an object can “interact with” through conduction & convection, before its temperature begins to rise, and thereby itself “conducts” heat to either the length of itself (such as a metal rod or pipe) or to other objects.

Ok so what does this physics mumbo jumbo mean?

• An object with low thermal conductivity will be able to “interact with” a LOT more heat before it transmits any of that heat to the rest of its structure, or to its “touching” or “neighboring” components. Keep this in mind for the next few discussions.
• Example: if we heat up one end of a steel pipe with a torch, how hot will the other side get over time, and how long will that take?
• Note: the actual value of (k) is not important in this discussion, but rather how it COMPARES across different materials we will be using to construct our intake.
• Also, the LOWER the value of (k), the BETTER it is to be used as intake components because it is LESS thermally conductive!

Radiation​

(credit: The Efficient Engineer)

The total amount of Radiation that reaches a surface, known as “Irradiation” (Ir) can be divided into 3 properties:

1. Reflection

(credit: The Efficient Engineer)


2. Transmission

(credit: The Efficient Engineer)


3. Absorption

(credit: The Efficient Engineer)

When thermal radiation reaches the surface of a certain object, these waves are either reflected by the object, transmitted through the object, or absorbed into the object.

The total amount of irradiation that reaches the surface of an object (Ir) is EQUAL to the SUM of the amount of radiation that is reflected (p), transmitted (t), and absorbed (α).

Ir = p + t + α​

(credit: The Efficient Engineer)

(credit: The Efficient Engineer)

So for instance (in simplest terms), let’s assume a black-colored high-temp silicone tube, commonly used in intakes, receives 100% of ALL thermal radiation aimed at it, giving it an Ir of 1. We know that since the silicone tube is opaque (or not translucent), that most of the thermal radiation will become absorbed right into it.

Thus, this piece of silicone tubing would have a Reflection ratio of 0.01, Transmission ratio of 0.01, and Absorption ratio of 0.98. This would mean the equation would be:

1(Ir) = 0.01(p or reflection) + 0.01(t or transmission) + 0.98(α or absorption)​

• Note that in the real world, all three of these 3 properties do occur at some degree in every material, however for simplicity’s sake, we will assume that any material that is translucent (completely clear like glass) shall have a transmissivity of 1, and any material that is opaque (not clear or translucent) shall have a transmissivity of LOW or ZERO.
• What matters is ONE of the 3 Irradiation properties (absorptivity, reflectivity, transmissivity) is usually dominant, and our focus shall be on ONLY the dominant one that occurs in the materials below.
• (VERY IMPORTANT) As Reflectivity increases, Absorptivity decreases, and the SHINIER and object, the higher reflectivity and the lower absorptivity it will have (this will be critical in our intake design)

Intake Materials & Properties​

Now we get into the meat and potatoes!

Let’s analyze a few different types of materials that are, or can be, commonly used in intake designs, or interact with intake designs, and let’s see how each material’s properties differ in terms of Thermal Conductivity (k), and how “sensitive” that material is in interacting with engine bay heat through Conduction (Cd), Convection (Cd), and Radiation (Ra).

• Note the values of Conduction, Convection, and Radiation are RELATIVE values in terms of the materials compared.

1. Carbon Fiber (ultra-high modulus of 110msi) (k) = 200

• (credit: Dragon Plate, DragonPlate | Engineered Carbon Fiber Composite Sheets, Tubes and Structural Components | Made in USA)
• This means:
  • (Cd) = high
  • (Cv) = high
  • (Ra) or (Ir)
    • p = low
    • α = high
    • t = low

2. Carbon Fiber (coal-pitch) (k) = 1000

• (credit: Aerospace Research Central, AIAA Aerospace Research Central)
• This means:
  • (Cd) = high
  • (Cv) = high
  • (Ra) or (Ir)
    • p = low
    • α = high
    • t = low

3. Carbon Fiber (polymer matrix) (k) = 1-10

• (credit: Aerospace Research Central, AIAA Aerospace Research Central)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = low
    • α = high
    • t = low

3. Epoxy Resin (k) = 0.2

• (credit: Scientific Reports, Improving the thermal conductivity of epoxy composites using a combustion-synthesized aggregated β-Si3N4 filler with randomly oriented grains - Scientific Reports.)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = low
    • α = low
    • t = high

4. Air (k) = 0.024

• (credit: Iowa State University, https://www.nde-ed.org/Physics/Materials/Physical_Chemical/ThermalConductivity.xhtml)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = low
    • α = low
    • t = high

5. Aluminum (k) = 205

• (credit: Iowa State University, https://www.nde-ed.org/Physics/Materials/Physical_Chemical/ThermalConductivity.xhtml)
• This means:
  • (Cd) = high
  • (Cv) = high
  • (Ra) or (Ir)
    • p = high (polished), medium (dull)
    • α = low (polished), medium (dull)
    • t = low

6. Steel (k) = 50.2

• (credit: Iowa State University, https://www.nde-ed.org/Physics/Materials/Physical_Chemical/ThermalConductivity.xhtml)
• This means:
  • (Cd) = medium
  • (Cv) = medium
  • (Ra) or (Ir)
    • p = high (polished), medium (dull)
    • α = low (polished), medium (dull)
    • t = low

7. Silicone Rubber (k) = 0.2

• (credit: Shin Etsu, https://www.shinetsusilicone-global.com/catalog/pdf/rubber_e.pdf)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = low
    • α = high (especially dark or black colors)
    • t = low

8. Nylon (k) = 0.2

• (credit: Material Properties, Polyamide - Nylon | Density, Strength, Melting Point, Thermal Conductivity)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = low
    • α = high (especially dark or black colors)
    • t = low

9. Polypropylene (k) = 0.2

• (credit: Material Properties, Polyamide - Nylon | Density, Strength, Melting Point, Thermal Conductivity)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = low
    • α = high (especially dark or black colors)
    • t = low

10.Polyethylene (k) = 0.5

• (credit: Material Properties, Polyamide - Nylon | Density, Strength, Melting Point, Thermal Conductivity)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = low
    • α = high (especially dark or black colors)
    • t = low

11. ABS Plastic (k) = 0.14-0.21

• (credit: C-Therm, The Thermal Conductivity of Unfilled Plastics – C-Therm Technologies Ltd.)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = low
    • α = high (especially dark or black colors)
    • t = low

12. Rubber (k) = 0.5

• (credit: Material Properties, Polyamide - Nylon | Density, Strength, Melting Point, Thermal Conductivity)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
  • p = low
  • α = high (especially dark or black colors)
  • t = low

13. Fiberglass (k) = 0.048

• (credit: Material Properties, Polyamide - Nylon | Density, Strength, Melting Point, Thermal Conductivity)
• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = medium
    • α = medium (since fiberglass is usually white or clear)
    • t = low

 

[AMG Aper]

SLK55 Engine Bay Observations​

When analyzing the stock SLK55 engine bay, lets jot down a few observations:

• That big V8 is crammed in a very tight space!
• Heat is emitted from all components of the engine, including the intake manifold, heads, engine block, primary cats (SUPER hot), and exhaust manifolds (one of the other hottest parts)
• There is nowhere for this heat to escape besides the two openings around the stock primary cats below the engine bay
• Heat trapped = more components in the engine bay absorb the engine heat
• Heat trapped = hot air trapped = under hood pressure increase = radiator is unable to flow the cooler outside air over its coils
  • (an effective exit suction must exist for the hot trapped engine air in order for the radiator to “suck in” cold air over its coils)
• The openings under the cats are not fully effective in evacuating hot air because hot air does not flow to the bottom the engine…why? Because HEAT RISES and gets stuck under the hood!

SLK55 Stock Intake Observations​

When analyzing the stock intake assembly, lets jot down a few observations:

• Air box sits on 4 rubberized-polymer (most likely the materials used) grommets, held in the air, not directly touching any metallic engine parts
  • Good: reduces heat conductivity from the engine to the air box
• Air box & tubing made most likely by polymer composites
  • Good: reduces chances of heat absorption by conduction and convection
• Air box & tubing is black in color (the piping) and grey (the air box)
  • Bad: dark colors are SUPER absorbers of thermal radiation
• Intake sits directly on top of the engine
  • Bad: even if conduction is eliminated by the 4 rubberized-polymer grommets, the hot air (convection) rises to the air box from the intake manifold (don’t forget: HOT AIR RISES), and radiative heat (radiation) is aimed directly at the air box, and since the air box and tubes are dark in color, they fully absorb radiative heat
• Front crash sensors are blocking the air inlet for the intake tubes
  • Bad: objects in the flow path can not only reduce the amount of air entering the intake, but can “disrupt” the smooth-flow of the airflow

Now, can we improve these aspects in the engine bay design, including the intake design, that takes care of the 2 major goals? (hint: YES WE CAN!)

1. Improve the flow of overall air by reducing flow restrictions
2. Reduce Intake Air Temperatures entering the intake manifold

My 1st solution? TrackSpec Hood Louvers!
​

NOTE: All of the temperature and flow observations that I noted during observing my stock and custom intakes, are AFTER installing my TrackSpec Hood Louvers. These louvers allow the hot high pressure air under the hood to naturally escape over the top, thereby allowing the radiator to channel more colder ambient air through its coils. This caused an overall improvement to heat reduction even with the stock intake, and greatly improved the efficiency of my 2 custom intake designs.

Let's now focus specifically on the rest of the engine bay and intake design.

My 2nd solution? Relocate the crash sensors!​

To improve the flow-rate of the stock intake, I began by FIRST relocating the front crash sensors UNDER the intake scoops. I unbolted them from where they hang on the frame, and drilled holes right into the intake scoops. Then, I simply bolted them into place with brand-new bolts threaded in the same pattern as the ones in the crash sensors (they are Metric I believe, but I forget the exact thread pitch).

This eliminated the HUGE blocky sensors that were right in the direct path of the perfectly-designed ram-air intake! Now, they will function just fine in the case of a crash, while not blocking the path of air our lovely M113 needs.

Now these initial fixes were done, off to the custom intake design #1!

Intake Design #1​

I began by purchasing two Specre Performance 4” inline air boxes that include polished aluminum housing and filters. These were the only air boxes that would fit under our hoods, and have a nice 3” opening to a 4” body with the filters inside, providing a straight-through unobstructed airpath.

Now notice I did not leave the aluminum metal of the Spectre air boxes the way they were, and instead covered them completely in high-temperature silicone tubing. Why?

Remember from our research on Aluminum:

Aluminum (k) = 205 (VERY HIGH)

• (Cd) = high conductivity
• (Cv) = high convection
• (Ra) or (Ir)
  • p = high (Spectre airbox is polished)
  • α = low (Spectre airbox is polished)
  • t = low

As we can see, Aluminum is GREAT at reflecting radiation when polished, but it is VERY CONDUCTIVE when it comes to conduction and convection.

Since our aluminum Spectre intake air boxes are not “touching” anything except the plastic distributor packs (which are a polymer material with very low thermal conductivity according to our material data), and since they are polished and reflecting most of the radiation occurring from the heat in the engine bay, we shouldn’t have a problem here, right?

Well, we completely forgot about the HOT AIR flowing over the aluminum, transferring a TON of heat through convection!

Now, can Silicone Rubber solve the convection problem of our aluminum Spectre intake air boxes? Well, if the silicone has a LOW Cv value, yes it can!

Silicone Rubber (k) = 0.2

• This means:
  • (Cd) = low
  • (Cv) = low
  • (Ra) or (Ir)
    • p = low
    • α = high (especially dark or black colors)
    • t = low

And there you have it! We solved the problem of conduction, convection, and radiation for our Spectre filters! (Or did we…see intake design #2 for why this design was slightly improved upon)

 

[AMG Aper]

Side Tubes​

Next, I purchased 2 carbon-fiber intake tubes, 3” in diameter, angled at 45 degrees

Being lightweight, super strong, and just plain AWESOME looking, carbon fiber was an easy choice! (Or was it?…Intake design #2 addresses this issue as well)

Initially I knew, but ignored, the fact that carbon fiber has a VERY WIDE RANGE of thermal conductivity (k) values, from anywhere between 1 to over 1,000! So the thermal conductivity of these tubes was a gamble for me, which meant the hot air could possibly affect these tubes VERY INTENSELY through convection…but I went ahead and used them because they looked amazing!

Also, when using the hard carbon fiber tubes , I ran into the issue of the passenger side rubbing against the battery cover vent area. There was no way of twisting this 45 degree tube to avoid contact, so I trimmed a little bit of the bottom portion of the battery cover to avoid rubbing, however this was something I did not want others to have to do as well, as not only are you cutting into the stock battery cover, but the vibration can erode the carbon fiber tube epoxy and scratch the actual carbon fibers.

• In intake design #2, I would actually ditch using the 45 degree carbon fiber tubes completely because of the rubbing issue, as well as because high-temp silicone tubes would not only provide a softer contact portion if in case there was any rubbing, but also because the silicone tubes would have a very low thermal conductivity in comparison to the carbon fiber.

Note: The Dipstick Tube is In The Way!​

(SUPER IMPORTANT) In this and Design #2, the oil dipstick tube was in the way and had to be cut & capped. Our cars do not come with a dipstick because the ECU can measure the oil life, so I thought it wouldn’t cause any functional issues. There was no way of getting the intake tubes around this without cutting.

For intake design #1, I purchased various silicone intake couplers to attach the stock plastic intake inlet hoses to the Spectre air boxes (as well as cover the entire Spectre air boxes), as well as to connect the carbon fiber tubes to our custom 304 stainless T pipe.

The hardest part for me in this Design #1 was figuring out a way to merge 2 intake pipes into the MAF housing. The biggest issue you will run into here, is that from the stock MAF housing to the bottom of the hood when closed, our cars have ONLY 3” of clearance, so any piping or T pipe taller than 3” will NOT fit here.

After searching for multiple types of T pipes, in all kinds of materials (from aluminum, polymer, steel), I could not find anything except possibly getting a used M113K intake T pipe (apparently, no Mercedes parts store that I researched sells these M113K T-pipes anymore, don’t know why!).

The reason I did not go for this T-pipe was because the two merges are in an oval shape, and I could not see how I would connect two circular intake pipes to an oval T pipe and have them fully seal. So, the search led me to an American stainless steel manufacturing firm that produced a beautiful 3” 3-way T pipe.

The Tee-Pipe​

Understanding that stainless steel had a relatively low thermal conductivity (especially for a metal part) touching an already low thermal conductivity polymer such as the MAF housing, and because I could not find another suitable 3-way pipe that could achieve my desired T pipe, I got this baby.

(credit: Pelican Parts, www.pelicanparts.com)

Now onto the MAF housing: I removed the polymer mesh that rests over the stock MAF housing using VERY THIN flat-head screw drivers in between the mesh and the MAF housing body, and gently angled the mesh upwards while I held pressure with my fingers from behind the screwdriver onto the MAF housing (to prevent the screwdriver from cracking the housing as I lift up the mesh).

Next, I gently removed the circular retaining spring, as well as the wire mesh resting in the housing.

After this I realized, I have not done any mods to help straighten the air in my custom stainless T pipe! So I went ahead and searched for a suitable mesh that I could insert into the lower portion of the T pipe that would help straighten the air just before the MAF sensor reads the airflow.

(credit: Performance MRP, www.performancemrp.com/)

(credit: Performance MRP, www.performancemrp.com/)



In my search, I came across a US-made aluminum mesh from a super friendly company named Performance MRP, and I installed it using high-temp silicone gasket maker sealant to hold it in place (the air straightener held just fine in the T pipe, but this gasket maker was just for extra security for preventing it from being sucked in the MAF housing during hard-throttle pedal-mashing.

According to MRP Performance:

“Our air straighteners are suitable for high-temp applications, they will hold up to being exposed to fuels as well as methanol injection. Our air straightener screens are used to aid in creating a laminar air flow at the mass air flow sensor. This will improve readings “fuel trim” from the MAF sensor, that ECU is seeing. Fix lean and rich spikes, improve throttle response and idle.”

• note in the following pictures you can’t see the silicone gasket-maker sealant, but I initially put a circular amount across the inner circumference of the bottom portion of the t pipe, then slid the aluminum mesh from the bottom onto the sealant, thereby getting the sealant all through the outer portion of the aluminum mesh fully through.

 

[AMG Aper]

Next I bolted the entire system together, and (what took me forever to figure out) using gorilla tape, wrapped 2-rounds of tape to the bottom of the T pipe to give it JUST enough thickness to squeeze through the MAF housing while creating a full seal from preventing engine-bay air from getting in. There was about 1-2mm of play when the T-pipe was inserted into the MAF housing, so the gorilla tape eliminated this play.

(credit: Home Deport, www.homedepot.com)

(credit: Home Deport, www.homedepot.com)

Also, just to cover the top portion of the MAF housing to T-pipe connection (to prevent dust and other debris from potentially getting into the MAF housing edges), I put a strip of EPDM rubber weatherstripping on the top-portion of the T-pipe that gets inserted into the MAF housing, thereby creating a nice yet flexible “seal”.

Alas, intake version #1 was done! And the improvements were significant! The throttle response was IMMEDIATELY noticeable by the seat of the pants, so we know the overall flow was much better thank stock…but what about the IAT improvements?

On average, these were my observations when comparing the Ambient Air Temp on the dash to my OBD IAT readings (again, this is WITH the TrackSpec hood louvers)

• Stock intake IAT – AAT = 20F to 30F
• Custom intake #1 IAT – AAT = 15F to 35F
  • Stock intake was more heat-resistant than custom intake #1 when sitting at 0mph idling
  • Stock intake took much longer to heat up, whereas Custom intake #1 heat-soaked at idle very quickly
  • Custom intake #1 was able to drop IAT-AAT below that of the stock intake once car was driving, but during stop and go as well as idling, it performed worse (heat-soak from sitting at idle)

 

[AMG Aper]

Intake Design #2​

Now before we get into the discussions of why I went from Intake Design #1 to #2, lets see what #2 looks like in comparison:

Now, lets compare this to the Design #1 and what it improved upon:

• Stock intake IAT – AAT = 20F to 30F
• Custom intake #1 IAT – AAT = 15F to 35F
• Custom intake #2 IAT – AAT = 5F to 20F
  • Custom intake #2 was slightly more heat-resistant than stock intake at stop-go and idling
  • Meaning the Custom intake #2 took slightly longer than the stock intake to heat-soak during idling
  • This means custom intake #2 beat the others at being more heat-resistant during idle (such as at stop-lights and traffic)

The improvements on Intake Design #2 focused on reducing the heat-soak effects of convection & radiation, whereby:

• Any part of the intake that was black in color, would absorb irradiation through absorption. Remember, opaque and dark-colored objects are magnets for thermal radiation absorption according to our previous discussions.
  • This meant that even thought the ABS plastic, silicone, & carbon fiber parts could have been excellent candidates for low conduction & convection, they were very strong absorbers of thermal radiation
• To reduce the chance that any black-colored parts could absorb heat through thermal irradiation, the solution was to wrap ALL opaque parts in a thin-sheet of aluminum foil
  • Remember, shiny aluminum has VERY HIGH irradiation reflectivity

BUT WAIT, Aluminum also has a very high thermal conductivity through convection (the hot air that would still flow over the foiled intake parts.

• Solution? Wrap the dark intake piping in low thermal conductivity fiberglass FIRST, then wrap the fiberglass-wrapped intake components in a layer of shiny aluminum.
• Fiberglass actually plays a 2-part role in reducing thermal conduction and convection by not only having a low thermal conductivity itself, but by having AIR POCKETS between the fibers that serve as an EVEN LOWER thermal conductivity rating!

(credit: Home Depot, www.homedepot.com)

• This means any engine heat will FIRST approach the outer aluminum layer, and a certain small amount of heat would ONLY be able to transfer through the aluminum from the hot air convection.
• When this happens, the layer of fiberglass and air pockets in between the fiberglass fibers, being both VERY LOW thermal conductivity, do not allow the convection heat absorbed through the aluminum to make it through to the underneath ABS and silicone tubes!
  • Again SUPER IMPORTANT: The fiberglass works better than simply covering the ABS / silicone tubes with the aluminum because fiberglass has AIR POCKETS within its fibers, which give it an EVEN LOWER combined thermal conductivity than ABS / silicone alone!

So in summary, Intake design #2 initially reflects MOST of the radiative heat by the use of thin aluminum, then the fiberglass / air stops the aluminum’s conductive heat transfer to the ABS / silicone components, and the ABS / silicone FURTHER reduces the chance of heat conducting to the aluminum Spectre Intake filters.

 

[AMG Aper]

Notes, Standards, & Thoughts​

Now, I did not have a flow bench to test out the actual flow characteristics of the stock intake vs the custom intake #1 and #2, so I was judging throttle response by the seat-of-the-pants feel. The more accurate way would be to use my OBD Link MX+ OBD2 reader and monitor the Mass Air Flow Rate (lb/min) relative to the car’s Absolute Throttle Position (0-100%) (which I did not get a chance to record in this test).

• When there is a higher Mass Air Flow Rate number for the same Throttle Position, this means that there is less restriction in the intake piping, allowing more molecules of air to enter the throttle body.
• let’s say, you are at 20% throttle position using the stock intake, and the MAF reads 20lb/min, and lets say at that SAME 20% throttle position using the custom intake, your MAF reads 22lb/min, you can safely assume your custom intake “flows” better than the stock one (assuming all other parameters such as ambient air temp, RPM, engine load, and other factors are the SAME in both cases)

Another way to do this, and probably more accurately, is to build a flow-bench yourself, by having a pressure gauge at the T-pipe, and a vacuum sucking in a set amount of air right behind it. Using the same vacuum and pressure gauge, test both systems, and the system that shows the “least difference” in the pressure gauge when the vacuum is on vs off, is the system that flows better.

• Remember, a vacuum causes pressures to generally fall below ambient, so if the intake is very restrictive, the vacuum will be able to “suck out” more ambient pressure and give a lower reading of pressure in comparison to ambient pressure.
• If this was done to a straight-piece of pipe, theoretically, the pressure would be the same when the vacuum was on vs off, because there is no “restriction” in the pipe from allowing the air flow

Final Thoughts (Feedback Appreciated!)​

In terms of the whole thermodynamics discussion we just went through, what are we trying to achieve here?

• Reduce Intake Air Temperature readings across a broad spectrum of RPM, load, and speed

Specifically the RPM, load, and speed I tested to give an apples to apples comparison of the stock and two intake designs, is testing the vehicle at the RPM, load, and speed of when we MOST USE OUR VEHICLES, which is HIGHWAY CRUISING.

Think about it, are we constantly romping on the gas pedal like how we love to use dyno numbers for everything? NO! Most of our vehicles spend their lives at cruising speed between 55-75mph, with of course the starts & stops on the streets meshed in with the occasional hitting the gas pedal just to see what she can do. So, considering this, I tested the car at these parameters:

• At 65mph
• roughly 2000 RPM
• no road grade or incline up or down (flat-straight driving)
• cruise control using the same engine load at 7th gear
• Engine fully warmed up (no cold testing)

Now, we need to understand that IAT (Intake Air Temperature) is just a number at a given point in the vehicle’s driving, but it by itself means NOTHING unless we compare it to AAT (Ambient Air Temperature)!

• IAT – AAT = how much is the ambient air that reaches our intake system HEATING UP BY OUR INTAKE before going into the intake manifold

My SLK55, as with probably a lot of other similar-generation cars, display the AAT in our dash, however (for some odd reason) this calculation is NOT AVAILABLE from our OBD port!

What this means is, that when I am running the OBD Link MX+ OBD reader (that can read, display, and record ALL available PID values the vehicle’s CPU is processing), I can only record IATs during my drive, but cannot record AAT in the same file!

So…what I need to do in the future is attach a thermometer that ALSO records temperatures right in front of the intake hose opening, zip tying it to the mesh grille. This will give me a solid recording of AATs in a separate CSV file, that I can combine with my OBD Link’s IAT file (you have to make sure the recording times line up in both files so that IAT and AAT are compared at EXACTLY the same time!

 

[AMG Aper]

Just an observation on the louvres.

IF the car is in a climate such as UK and used in all weather types then they add another set of entry points for water.
The SLK engines (all of them) hate water.

You ae fortunate to live in a relatively dry climate.

Thanks for your observation! Is there certain entry points where water could be a problem? I can't imagine much of an issue unless water gets directly into the intake, cabin filter, battery, or similar areas.

I've taken it to multiple car washes and so far have not noticed an issue, but again would love to hear about any issues you've come across.

 

[Avel Du]

The vent above the fuse/SAM box that is already there has caused issues for some.
The vent above the battery, coupled with a blocked drain hole has caused issues for some.

Having vents lower down? Time will tell.

 

[Turbo]

I haven't read through all of it yet, it's late and I need to get some sleep. I'll read it tomorrow, from start to finish..

But I was just thinking, maybe you're looking in the wrong place!? Not protecting the intake air from the heat, but getting the heat out of the engine bay is a better option?

There's only ONE place where heat can escape (easily), and that's the air .. "hole" opposite the battery box - for us here in the UK, it's the driver side air vent.. It is not large!! The whole car is covered in plastic covers underneath, so no air can escape (in large amounts?) that way, there's no escape on the sides.. It all just collects in the engine bay!


I read/saw a video about the latest Aston Martin F1 or Valkery or whatever it was (I think it was the AM at least, it was a while ago) and they've spent tons of money solving the REAL problem - getting the heat out..

They thermal/ceramic coated the headers (that in itself solves most of the heat-under-the-bonnet problem), they opened up the fenders and even had huge scoops in the bonnet, all to get the hot air out.


Solve the problem of WHY it's so hot under the bonnet, and maybe you don't have too try too solve a problem that might not exists??

 

[AMG Aper]

I haven't read through all of it yet, it's late and I need to get some sleep. I'll read it tomorrow, from start to finish..

But I was just thinking, maybe you're looking in the wrong place!? Not protecting the intake air from the heat, but getting the heat out of the engine bay is a better option?

There's only ONE place where heat can escape (easily), and that's the air .. "hole" opposite the battery box - for us here in the UK, it's the driver side air vent.. It is not large!! The whole car is covered in plastic covers underneath, so no air can escape (in large amounts?) that way, there's no escape on the sides.. It all just collects in the engine bay!


I read/saw a video about the latest Aston Martin F1 or Valkery or whatever it was (I think it was the AM at least, it was a while ago) and they've spent tons of money solving the REAL problem - getting the heat out..

They thermal/ceramic coated the headers (that in itself solves most of the heat-under-the-bonnet problem), they opened up the fenders and even had huge scoops in the bonnet, all to get the hot air out.


Solve the problem of WHY it's so hot under the bonnet, and maybe you don't have too try too solve a problem that might not exists??

Hey Turbo, that was my first fix with the Trackspec hood louvers

It was probably the best functional upgrade I could do initially, but the intake could be improved which is why I jotted down the results after my upgrades.

The other biggest restriction I need to attack is the crappy exhaust manifolds, I have MBH headers sitting in my garage ready to be put on.

 

[cyberdrakon]

I haven't read through all of it yet, it's late and I need to get some sleep. I'll read it tomorrow, from start to finish..

But I was just thinking, maybe you're looking in the wrong place!? Not protecting the intake air from the heat, but getting the heat out of the engine bay is a better option?

There's only ONE place where heat can escape (easily), and that's the air .. "hole" opposite the battery box - for us here in the UK, it's the driver side air vent.. It is not large!! The whole car is covered in plastic covers underneath, so no air can escape (in large amounts?) that way, there's no escape on the sides.. It all just collects in the engine bay!

They thermal/ceramic coated the headers (that in itself solves most of the heat-under-the-bonnet problem), they opened up the fenders and even had huge scoops in the bonnet, all to get the hot air out.

The holes near the windshield are actually intakes as they are in the high pressure zone when the car is moving.
That's the reason I put the holes in my hood right after the radiator, and vents in my fender. The problem with the fender vents is that without other mods, there's only about 2 cm where engine air can get into the side fenders.

 

[cyberdrakon]

The other biggest restriction I need to attack is the crappy exhaust manifolds, I have MBH headers sitting in my garage ready to be put on.

Get the swaintech ceramic on the headers. Don't bother coating the short pipes on the bottom.

 

[AMG Aper]

Get the swaintech ceramic on the headers. Don't bother coating the short pipes on the bottom.

Too late but thanks for the advice! Got Cerakote glacier black on headers and downpipes.

 

[260DET]

Wow! Great to see such a in depth analysis of a problem and what you did to address it. A couple of comments, bonnet vents are a bit of an art which I have looked at and satisfactorily sorted on another car. Basically they need to have a deflector in front of them to direct the air up from the vent itself to form a low pressure area above the vent which facilitates air extraction. Alternatively the vent can be recessed for the same purpose but this is more likely to be done originally, DIY can be difficult.

Secondly your T piece is too abrupt in turning the air 90 degrees, it needs to have a more gentle or flared transition. I've done some research on this subject, it must be kept in mind that air like water does not like changing direction so the bends must reflect this. Your relatively tight turning T piece will definitely reduce flow. No criticism intended, just trying to improve an already very nice piece of work.

 

[Turbo]

Ok, that is a marvelous article! Very interesting, truly.


But.. NUMBERS!!

We’re going to have to get rollig road numbers . How much does it actually do? It’s a lot of work (and money!) if it only give ”a few” extra ponnies.

Which seems to be the case. Your #1 looks remarkably identical to over-the-counter intakes that’s out there, and numbers on those indikate less than 5hp (2-3 is the last number I’ve seen) improvement..

 

[cyberdrakon]

Too late but thanks for the advice! Got Cerakote glacier black on headers and downpipes.

Ah, I got cerakote as well as it wasn't possible to get swaintech where I am.

 

[cyberdrakon]

Too late but thanks for the advice! Got Cerakote glacier black on headers and downpipes.

I thought you got MBH? The headers don't have separate downpipes. For the little pipes at the end, they had to be cut and welded to attach to my exhaust, so coating them just makes it harder on the installer.

 

[AMG Aper]

I thought you got MBH? The headers don't have separate downpipes. For the little pipes at the end, they had to be cut and welded to attach to my exhaust, so coating them just makes it harder on the installer.

Yup I do have MBH, but I found out about the downpipes not being aligned correctly after I had the cerakote done.

I might even use a flex pipe instead of the downpipes just to control a bit of engine movement

 

[AMG Aper]

The holes near the windshield are actually intakes as they are in the high pressure zone when the car is moving.
That's the reason I put the holes in my hood right after the radiator, and vents in my fender. The problem with the fender vents is that without other mods, there's only about 2 cm where engine air can get into the side fenders.

I need to tape yarn or wool tufts to the hood in multiple areas and see how the pressure is affected around the stock vents. I might need to close them because yes, it is believed that there is enough high pressure that it can cause air to go back in instead of coming out (like the vents).

 

[AMG Aper]

Wow! Great to see such a in depth analysis of a problem and what you did to address it. A couple of comments, bonnet vents are a bit of an art which I have looked at and satisfactorily sorted on another car. Basically they need to have a deflector in front of them to direct the air up from the vent itself to form a low pressure area above the vent which facilitates air extraction. Alternatively the vent can be recessed for the same purpose but this is more likely to be done originally, DIY can be difficult.

Secondly your T piece is too abrupt in turning the air 90 degrees, it needs to have a more gentle or flared transition. I've done some research on this subject, it must be kept in mind that air like water does not like changing direction so the bends must reflect this. Your relatively tight turning T piece will definitely reduce flow. No criticism intended, just trying to improve an already very nice piece of work.

You are absolutely correct on both fronts. I need to contact TrackSpec Motorsports to see if they can make a set of deflectors to improve the suction effect.

As far as the Tee pipe, you are correct, but I am unable to find a smooth transitioning Tee section that can fit under our hood. We have EXACTLY 3 inches of space from the MAF sensor housing to the bottom of the hood. The Tee pipe I have is exactly 3 inches.

The only way I can see using a smoother transition is by doing a hood scoop intake with the hood cut open and a 90 degree filter and tube put into place, or maybe using the E55 plastic intake y pipe.