S54 Velocity Stacks - FAQ's

  1. What does the kit include?


The conversion includes all the mechanical components required to convert the vehicle to running Velocity Stacks:
-Replacement intake trumpets/velocity stacks x6
-Modified OEM front air intake duct
-Billet Oil Catch tank
-Oil Pipes and clamps
-6 Custom ITG Velocity Stack Air Filters
-Idle Control Air Filter
-IAT (intake air temperature) Sensor and wiring harness
-Carbon Fibre Heat Shield
-Intake Boots x6
-Air Feed Pipe
-Jubilee Clamps x12
-Silicon Vacuum Line Blank
-Billet Oil Return Feed Blank and pipe work
-Cable ties, fixings and connectors


  1. Are there any optional extras available?


We do have optional extras to further compliment or customize the kit, these include coloured intake boots at a cost of £45.30 ($65US) and a remote Custom Alpha-N map/tune tailored to the individual car from TTFS (www.tuningtechfs.com) at a cost of £675.00 ($849.00US)


  1. How much does everything cost in total?


Prices £1100 (about $1450US) including painting the Velocity Stacks in a colour of your choice, plus shipping Circa £50 ($75.00US.) the price of our optional extras are highlighted above. Please get in touch for the latest pricing.


  1. How long does it take to produce?     


It would take around 2-3 weeks for us to produce a kit for you, we normally have a kit ready to ship in less than that but we don't want to promise something we can't deliver.


  1. Do I have to worry about heat soak with this kit? 

It is important to understand the phenomenon known as "heat soak" and the fear that it has instilled in so many! “Heat Soak” occurs when the engine is turned off, not during engine running, especially on normally aspirated cars. It is also far more of an issue in forced induction applications.


When an engine is switched off, the combustion process is terminated. This terminates the momentum of the crankshaft, which in turn stops the turning of the water pump. As the coolant is no longer being circulated, the engine block and cylinder temperature increase for a period of approximately 3 to 10 minutes, depending on the engine design and additional components, with an S54 for example this period is closer to the 10 minute mark due to the design and material of the engine block.


During this time, the engine block radiates heat to the air surrounding the engine, which is slowly cooling the engine. However, the cooling process occurs very slowly, and as a result, the temperature of the engine block transfers the heat to the coolant and in turn other components in the engine bay. The coolant temperature increases, which in turn increases the pressure inside the coolant system. This is why the vehicle's coolant temperature gauge increases over a period of time after the engine has been turned off and why it’s a rubbish idea to remove the expansion tank filler cap during this time! I’m sure we’ve all tried it!


The components that “Heat Soak” on an S54 OEM Intake system are the intake charge pipe and to a greater extent the “Intake Air Temperature” (IAT) Sensor located within the MAF (Mass Air Flow) Sensor. This is why companies sell IAT relocation kits. As said the “Heat Soak” occurs in the main when the engine is off and the car is no longer provided with a cool flow of fresh air, from either the fan or as a feed from the front of the car during driving. The oem airbox, (filter housing) and Intake Plenum can “Heat Soak” too during this period, during normal driving this does not occur, the cooling system does a good job of keeping the engine temp down, and a good feed of fresh air from outside the engine bay helps the engine run efficiently and keeps things cool.


The reason why K&N Style filters cause poor running and a reduction in power is not due to “heat soak” as defined above, the main reason is because they are “oiled” filters, the oil forms a coating on the IAT/MAF which over time degrades the sensor, They can also be more restrictive then an OEM filter as they are not oiled, The oil gets ingested by the engine and sticks on the IAT within the MAF on it’s way through the intake system. This reduces the sensors ability to withstand heat from the air surrounding it. Meaning the sensor can read false temps, (the engine believes the air temp to be higher than it actually is causing a reduction in power) The ECU will actually retard timing to compensate for these higher temps giving the reduction in power.


With regards to my Intake kit, for years racing teams, rally cars and engine builders have been running “Velocity Stacks” without any concerns for “Heat Soak”, it was with this in mind I spent a year researching what heat soak is and what it affects. I drive our demo car (my car) daily and have done for the last 2 years and now for over 20k miles. The key to the conversion is good ducting of cold air to maintain healthy cool air flow. The IAT Sensor I use in my kit, as with any other IAT sensor needs to be mounted to give an accurate representation of the air temp being seen by the engine/ecu. For that reason it's mounted between stacks 3/4 on a custom bracket or Carbon Fibre heat shield, depending on which option is chosen.


I have been monitoring iat's for the duration of the 2 years I've been running the conversion and can report that when driving iat's are no different to those with the OEM intake, if anything the conversion provides a better flow of cool air to the velocity stacks, as with the OEM intake or a Carbon Airbox this does creep up when stopped in traffic for example, but as soon as the car moves and air flow resumes the temps fall far quicker than with any other style intake, I've done extensive research into it.


The Velocity Stacks and Filters Cool very quickly due to the nature of the materials they are made from, when supplied with a cool flow of fresh air, far quicker than the OEM intake system which stays hot for ages! Anyone who has opened their bonnet after a drive and felt the temp of the Intake system knows how hot this can get, all that black plastic does a great job of retaining heat!


Here is a Rolling road printout showing Wheel Horse Power and Wheel Torque for my car, as you can see, no problems with the graphs, throttle response is unbelievable as the system is so unrestrictive. It also makes good power and reliability isn't effected. 


Rolling Road Print Out


      6. Is a tune reqired for this to function properly?


Yes an Alpha-N tune is required for this to function properly We are proud to announce that TTFS (www.tuningtechfs.com) has paired with us and can offer bespoke remote tunes through us to go along with the kit.


Lets discuss what Alpha-N is:-


I’ll first talk about Alpha-N and then talk about how it relates to S54’s as fitted to E46 M3's and Z4M's. I’ll use real world examples also.

Before I start discussing what Alpha-N is, let me explain what Alpha-N isn’t.

Alpha-N by itself is not a “tune” and its not better or worse inherently by itself. It has specific applications and benefits/drawbacks just like anything else.

Alpha-N is nothing more than a method to calculate engine flow. Thats it. The ability to properly calibrate an engine or “tune” is entirely dependent on the ECU’s ability to calculate the flow of air through the engine at any given tiny interval of time. The more accurately the ECU can do this and the smaller the time interval it can update this flow number, the better.

What do I mean by “Flow”? The ECU’s job is not to calculate the volume of air flowing through an engine. Technically its job isn’t even to calculate the mass of air flowing into the engine. Its job is to calculate the mass of Oxygen flowing into the engine. That only makes up about ~21% of the air in the atmosphere here on planet earth. This composition can slightly vary. Oxygen is the reactant thats used with fuel during combustion.

That is where we convert chemical potential energy into usable heat energy. The more heat energy combustion generates, the more average force it applies on the piston through the relevant time interval and well…you can take it from there.

How does the ECU calculate the amount of oxygen flying through it?

Two things: Sensors and Assumptions. In reality everything is based on assumptions at a certain extent.

A lot of load calculation by the ECU is done by assumptions. Now, a lot of people are saying

“Stop right there, how can that be a good thing? That can’t be an accurate method can it?”.

It can and it is...IF its done correctly.

Assuming everything is working right, ECU’s make assumptions about things that they don’t expect to change and make measurements (with sensors) of things that are expected to change.

A big example of an “assumption” the ECU makes is injector flow. An ECU is programmed to know that its injectors will ALWAYS flow a certain amount of a fuel when it commands a certain pulse width. It makes this assumption because it doesn’t expect the fuel pressure or injectors to change. If those two things do not change then the ECU can always assume that at a certain pulse width the flow will be a certain mass of fuel. If you change the injectors or fuel pressure, it makes its assumptions inaccurate. It will get different fuel flow for the same injector pulse width as before. As a result in closed loop, your trims will start to change to adjust for this. Your WOT AFR’s will be different too. If you had a fuel flow sensor, then you can program an ECU so that a change in the fuel system can be accounted for. The S62 ECU and most ECU’s however do not expect the fuel system to change because thats modification and so therefore do not need sensors to take measurements. They can get away with assuming its an unchanging variable.

That is the entire point of “tuning”. Tuning is done when you change things the ECU assumes shouldn’t change though not exclusively. That is fuel flow or airflow. With enough sensors and advanced enough software you can make a self-tuning ECU and that is actually not that difficult to program.

Anyway, lets continue:

An example of something thats measured with a sensor is mass air flow via voltage. An ECU has a MAF flow curve that tells it at Voltage=X then Flow=Y. In reality however this too is kind of an assumption. What can cause this assumption to be inaccurate? A leak after the sensor perhaps, or maybe buildup of any insulating residue on the wire in the MAF sensor. You’re measuring it, but you’re also assuming that you have no leaks or any other factors that can change. As I said before, we’re assuming everything is working properly.

A MAF sensor is one way to account for changes in the atmosphere that matter. A MAF sensor accounts for air density (which is affected by pressure and temperature). That is how it determines the mass/time of flow.

If you increase the flow of air through the wire, it cools it. If you flow the same volume of air but increase density (either by pressure or temperature) then the wire once again gets cooler as the air becomes more thermally conductive so it pulls heat away. All of these things affect the voltage and therefore the MAF sensor can account for the mass of air flowing through at a pretty astonishing accuracy in steady-state conditions.

The best part of a MAF sensor is that it not only accounts for atmospheric changes, but it directly sees the amount of air your engine is pulling in. Open the throttle further? More voltage. Increase RPM? More voltage.

In fact, accounting for atmospheric changes is REALLY easy no matter what you do: MAF, MAP, or Alpha-N.

The beauty of a MAF is that it accounts for changes in engine VE and that is why its so common on street cars for emissions.

For example, clogged air filters change engine VE. A change in engine VE always requires a re-tune on a MAP sensor setup or Alpha-N, otherwise fuel trims start to wander and lambda control becomes less consistent. On street cars, many of which are neglected, a MAF is an amazing way to make sure the car drives good and keeps AFR’s at the stable Lambda=1 regardless of whats happening.

Lets continue:

A quick note: A MAF cannot really account for oxygen content, but thats okay. Atmospheric Oxygen content hardly varies and we can leave that to an assumption because it will lead to unnoticeable margins of error.

Continuing on:

There is another entirely different method of calculating airflow and this type of calculation is called “Volumetric Efficiency”.

A MAF sensor system doesn’t care about volumetric efficiency of an engine. Whatever the engine flows is what it flows and that will be measured by the MAF. When you don’t have a MAF and you’re not measuring flow…you need to somehow come up with a value of flow using more indirect methods.

These indirect methods are not inherently less accurate or less capable. It all depends on how they are done in practice.

The two ways I’m talking about are using a TPS or a MAP sensor. The former method is commonly known as Alpha-N and the latter is known as Speed-Density.

Lets take a step back and look at how they work on a fundamental level.

If you run an engine at a certain throttle angle opening and then run it at a certain RPM, its flow VOLUME will ALWAYS be the same assuming nothing else changes. If you take an engine and create a certain pressure in its manifold at a certain RPM, it will always flow the same in those characteristics assuming nothing else changes.

So what we can do is start building tables in the ECU basically that say this:

If Manifold Pressure=X AND RPM=Y THEN VE %=Z

with Alpha-N its the same thing except:

If Throttle Angle=X AND RPM=Y THEN VE %=Z

This is VE tuning. You have to measure the VE in as many possible combinations of engine operations as you can. The finer you go, the higher the resolution and the more accurate it is. For example you can measure VE in increments of 100RPM or increments of 10RPM. You can measure VE in increments of 1 PSI of pressure or every .1 PSI of pressure. You can measure VE in increments of 1% throttle angles or 10% throttle angles. A table of VE can be lets say…32x32 cells. Thats a resolution that gives you 32 increments of RPM and 32 increments of your controlling sensor which is a TPS for Alpha-N or manifold pressure for speed density. Anything in between can be interpolated or the closest cell is used so margin of error is within tolerances.

This can be used to calculate the VOLUME of airflow at any RPM and throttle angle. Part of the work is done.

So how do we get mass? Easy, an IAT sensor and Barometric pressure sensor.

Our formula can look more like this now:

If Throttle Angle=X AND RPM=Y AND IAT=A AND Pressure=B THEN Mass flow = some value of mass/time.

you can also rewrite it to be

If Throttle Angle=X AND RPM=Y THEN VE %=Z and then take the Z value and correct that volume to temperature and pressure to find density. From there you get mass. It doesn’t matter what order, the logic works here.

Now lets to get to when Alpha-N is better and when MAP is better.

Alpha-N works just fine for NA and SC’d engines. The reason is because flow of the supercharger is constant and directly related to RPM so we can make an assumption about that without actively measuring it on the street just like a naturally aspirated engine. It can get a bit complicated during rapid acceleration of RPM, but it still works within tolerances.

On a turbocharger, boost changes all the time and is not consistent at all with throttle so making assumptions is impractical (but not impossible, with enough sensors you can do it). Thats why MAP sensors are used for turbos. A MAF also works for this, but due to a very long and complicated reason, in my opinion a MAP is better for turbochargers.

Real race cars using Alpha-N generally don’t have “closed loop” with O2’s. Street cars do and IMO a more accurate way of calling it would be MAFless. O2s are a big deal. Just like with a MAF sensor, the O2s can actively check AFR and make corrections for stability during part throttle operations.

Now lets move on to S54’s.

S54’s still use O2s to make corrections in Alpha-N operation. With a MAF system, the ECU takes a reading of flow, then provides fuel and then sees feedback from the O2 to oscillate at the stoichiometric lambda. With Alpha-N the ECU uses its formulas (or you can call them look-up tables) to deliver fuel in the same way and then checks accuracy from the O2 sensors.

The downside to Alpha-N (and MAP sensors) is that ANY change at all to the engine will toss its VE assumptions and can lead to drivability problems if they are big changes. With Alpha-N the engine has no idea if you changed a flow characteristic. A MAF is a lot more tolerant of that because any change that changes flow will affect voltage and the ECU can see that to appropriately compensate. That is why fuel trims don’t really change as the weather changes or when you install mods on a MAF car.

On an Alpha-N car, every modification you do or even a clogged filter will blindside the ECU.

For example on a MAF car, take an S54 and add a completely overhauled exhaust with headers, X-Pipe, wider piping and higher flow cats. I can also installed bored throttles, better stacks, less restrictive filters…etc. It doesn’t matter what I change before or after the MAF. The MAF measures flow and the car will start right up and drive even though I may have just drastically changed the VE at every RPM and throttle combination.

On an Alpha-N car you might have horrible drivability if the changes are large enough and it may require quite some work to model the air flow. The ECU does not know whats going on and therefore must be calibrated. By the way, on an exclusively MAP sensor based ECU, the same rules apply.

Ambient pressure can change a lot between regions (mainly altitude), but not usually so much in a single region so that can accounted for in custom tuning much like your modifications.

To summarize, if Alpha-N is done correctly then there is no problem or worry in running it. It works just fine for a naturally aspirated or supercharged engine. There is no inherent deficiency in this system over a MAF sensor for this type of engine. The key words are that it has to be done right and that is entirely dependent on the tune itself.

For this reason we use TTFS performance tunes to get the very best from our intake conversions.



  1. Does this kit address the lack of MAF, and other related sensors associated with the removal of an OEM air box?


There are only 3 connections to the oem intake if you don't include the MAF. These are, oil breather return, (hence the oil catch tank and pipe work with our kit), sump drain return, again (hence the billet blank and pipe work with our kit specifically for this application), and finally a brake servo bleed airline (our kit provides a silicon blank for this), the removal of the brake servo bleed airline doesn't detrimentally affect the efficiency of the brake servo or the cars braking ability, we have performed lengthy tests to ensure this is true, and found it to be so.


  1. How does this conversion cope with everyday driving conditions?


This kit has been tested extensively on our demo E46 M3 which is driven daily we have covered approximately 20,000 miles over a 2 year testing period and we have found no substantial impacts on drivability, and it responds well to all types of driving environments and weather conditions.  The conversion responds very similarly to oem at low rpm (sub 3.5k rpm) and then comes into its true power at mid to high range power.


  1. Are there other customer reviews of the product to read?






      10. How do I order a kit?


Email Info@psdesigns.global

Use the contact us page of the website 


Please don't hesitate to get in touch if you have any questions or if you'd like to enquire about ordering a kit, we will ensure your bespoke conversion is tailored to meet your exacting needs. 


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