Forced Induction Explained

[Burgy]

This thread is to teach guys about forced induction. I will be talking about simple things like blow off valves all the way to Ignition timing etc.

Please feel free to comment with any technical questions or statements.

I will be explaining everything SIMPLY, this thread is for guys who have minimal or average knowledge of forced induction systems.

Turbo Basics

There are 3 parts to a turbo charger:

The compressor side, which includes compressor wheel and housing.

The Turbine or exhaust side, this includes exhaust wheel and turbine housing.

The turbo core, this includes connections for oil in and out, and some turbos, water in and out. The core houses the shaft that the compressor and turbine wheels spin on. This shaft either runs on a bush, single ball bearing or dual ball bearing.


Ok cool, now how do these things create boost?

Exhaust gas exits the motor into the exhaust manifold, the gas then passes through the turbine side of the turbo and spins the turbine wheel. The gas then exits the turbo via the downpipe.
The Turbine wheel and compressor wheel are connected via a shaft, so when the exhaust wheel spins, the compressor wheel spins. This is what creates boost.
The amount of exhaust gas that enters the Turbine housing has to be controlled, otherwise, the turbo will boost higher than desired. This is done via the actuator or wastegate. The actuator or wastegate is set to a certain PSI and will open once it reaches this PSI. The left over exhaust gas is then expelled via a ‘dump pipe’ – This is either a custom pipe or build into the downpipe. Open dump refers to a wastegate that expels exhaust gasses to free air.
The wastegate or actuator vacuum lines are connected to the intake manifold, therefore allowing it to accurately measure the amount of boost being produced by the turbo.
After this process, the compressor wheel is now spinning. It is sucking air in via the intake and pushing it out towards the intercooler and throttle(s). The faster the wheel spins, the more boost that can be produced.

more soon..

 

[Burgy]

Reserved.

 

[Crash_Nemesis]

Burgy... I have a question...

When can you and I race each other... Supercharged M3 vs Turbo Charged M3... :fencelook:

 

[Riaan335]

Question:

Whats better for maintaining/achieving higher boost - more air(volume) or colder air(IAT)???

 

[zaleonardz]

Well one does tend to go quite south in a porno ?

This thread hasnt even started properly yet, and already its going south...:fencelook:

Question:

Whats better for maintaining/achieving higher boost - more air(volume) or colder air(IAT)???

This is actually a good question, One could argue that boost out of a turbo, even with intercooler is naturally hotter then that of a supercharger, due to the turbo itself as its drive is attributed to super heated exhaust gasses.

Not that the supercharger does not generates any heat during operation, but the heat caused is due to mechanical friction, and not the product of a chemical explosion.

One would say that the colder the air in the combustion chamber is, when mixed with the fuel, the more intese the explosion would be.

Or am i talking crap, I have already had my sleeping pill so I may turn into a fluffy bunny in like 50 seconds or so..

 

[Riaan335]

I'm not trying to be funny Leonard, so yes, I hope it is a good question.

Been reading up on the different CAI/DCI's on the x35's this week.

After lots of reading, I'm still on the fence.

If you could induce colder air through your intake, the air passing through would naturally be cooler in the combustion chamber.

IMO, there is only really one CAI system on the market for the x35 platform, and that is the Stett CAI. Then BMS, aFE et al all are in the engine compartment, sucking hot air, especially in slow driving situations.

What I'm trying to figure out is, is the stock airbox, which BTW is very restrictive regarding flow, better at maintaining cooler intake temps, whereas the BMS or other DCI's deliver greater air volumes, albeit at slightly higher IAT's???? Or does the BMS for instance achieve lower IAT's?

In short, to achieve target boost, is it better to have slightly higher IAT's or better/more air volume???

I hope I'm making sense here.

Disclaimer: Named intakes are what is popular on the market. I am not degrading or bashing any brands here. I know the manufacturers of said products have done lots of R&D on their products. I'm merely trying to figure out this issue for myself. I would like to get more input regarding this though from more South African fanatics, as opposed to the American info on the interwebs

 

[P1000]

Question:

Whats better for maintaining/achieving higher boost - more air(volume) or colder air(IAT)???

This is actually a good question, One could argue that boost out of a turbo, even with intercooler is naturally hotter then that of a supercharger, due to the turbo itself as its drive is attributed to super heated exhaust gasses.

Not that the supercharger does not generates any heat during operation, but the heat caused is due to mechanical friction, and not the product of a chemical explosion.

Or am i talking crap, I have already had my sleeping pill so I may turn into a fluffy bunny in like 50 seconds or so..

Superchargers will heat the air more for the same boost+volume. Simply because they are less efficient in most cases. The exhaust gasses have very little contribution to the heating of the intake air in a turbo - by far the biggest component of heat comes from the thermodynamic effect of compressing air.

The original question:

Whats better for maintaining/achieving higher boost - more air(volume) or colder air(IAT)???

Does not make any sense to me. Colder air is more dense per definition and thus contains more oxygen. So say you are boosting 1bar@80degreeC compared to 1bar@50degreeC, the lower temperature will have a lot more oxygen, which means it can burn more petrol which means more power. If you want more boost, you need a bigger volume of air for the gas equations to still follow the laws of physics, simple.

Of course, the amount of boost you can safely run on an engine is highly dependant on the compression ratio of the engine and combustion chamber design as well as how well you can mix the petrol with the air(swirl) etc. With the advent of direct injection, where the injection of the petrol can be controlled to the point of at what degree in relation to the engine stroke the fuel gets injected, the game changed and crazy boost/compression ratio configurations have become possible.

 

[Riaan335]

Thanks P1000, I forgot about that - Colder air is more dense.
So in essence, if you can induce colder air, but less volume, compared to a greater volume hot air, the cold air would be optimal for the combustion cycle as opposed to the hotter greater volume.

I'm just trying to understand how to achieve/maintain boost with regards to air in the combustion cycle.

I think I should go to bed and do a bit more reading on this.

Anyway, didn't mean to highjack the thread, looking forward to what Burgy is planning to share with us.
If my posts are off topic, mods can delete or whatever.

 

[P1000]

Thanks P1000, I forgot about that - Colder air is more dense.
So in essence, if you can induce colder air, but less volume, compared to a greater volume hot air, the cold air would be optimal for the combustion cycle as opposed to the hotter greater volume.

No, in my example, I assume the volume is identical. The volume of compressed air would be solely dependant on the displacement of the engine and the engine speed (RPM) (taking volumetric efficiency into account).

Aftermarket CAI is not worth much in a turbo system, unless the OEM design is done poorly, which most FI BMWs I've seen aren't. Sure, to the guy selling you the system, they are worth a lot of cash in pocket, so don't believe to much they tell you. If you want more power, get a well-designed bigger intercooler and manage boost levels throughout the rev range. Of course, many things can be done which all add up, but I think that we need to stick to the scope of the topic here.

 

[Riaan335]

Well lets get some numbers up here, and then i'll see how many to bring in.
So far, excluding shipping youre looking at R175 a plug. For the Bosch plugs!
If you want the plug sockets as well let me know. Plug sockets are R285 ex shipping!
Please note this is for the N54 only! I really dont know if this will fit the N55!

Thanks P1000, I forgot about that - Colder air is more dense.
So in essence, if you can induce colder air, but less volume, compared to a greater volume hot air, the cold air would be optimal for the combustion cycle as opposed to the hotter greater volume.

No, in my example, I assume the volume is identical. The volume of compressed air would be solely dependant on the displacement of the engine and the engine speed (RPM) (taking volumetric efficiency into account).

Aftermarket CAI is not worth much in a turbo system, unless the OEM design is done poorly, which most FI BMWs I've seen aren't. Sure, to the guy selling you the system, they are worth a lot of cash in pocket, so don't believe to much they tell you. If you want more power, get a well-designed bigger intercooler and manage boost levels throughout the rev range. Of course, many things can be done which all add up, but I think that we need to stick to the scope of the topic here.

Thanks. You helped more than you probably realise.

So yes, lets keep it on topic, and see what Burgy has to say.

 

[bmsportzn135i]

Also, maybe those with the proper knowlage can chip in here. But putting cones on a turbo, doesnt mean more air passing thru, but rather a less restrictive passage for the air to pass. So there for less strain on the turbos? Same as running down pipes, instead of having cats in place, its just helps the turbos spin more freely!

 

[Burgy]

Question:

Whats better for maintaining/achieving higher boost - more air(volume) or colder air(IAT)???

Thats actually quite a complicated question, when I put my first post about turbo basics, it should shed some light.

In a nutshell, higher boost is produced by the actuator or wastegate. This can be done with mapping or mechanically.

Achieving higher boost is easy, maintaining it is a little more difficult. Stock turbos will peak early and then drop off. This happens because the turbos are small, the AR or size of the exhaust side cannot hold the boost - this is very much in a nutshell, other factors do play a part.

When talking about air volume with intakes, we refer to grams/sec of air. This is recorded usually by the MAF sensor. More grams = more volume BUT because colder air is denser than hot air, colder air also means more volume.

 

[Burgy]

Does not make any sense to me. Colder air is more dense per definition and thus contains more oxygen. So say you are boosting 1bar@80degreeC compared to 1bar@50degreeC, the lower temperature will have a lot more oxygen, which means it can burn more petrol which means more power. If you want more boost, you need a bigger volume of air for the gas equations to still follow the laws of physics, simple.

Of course, the amount of boost you can safely run on an engine is highly dependant on the compression ratio of the engine and combustion chamber design as well as how well you can mix the petrol with the air(swirl) etc. With the advent of direct injection, where the injection of the petrol can be controlled to the point of at what degree in relation to the engine stroke the fuel gets injected, the game changed and crazy boost/compression ratio configurations have become possible.
[/quote]


100% correct.

 

[Burgy]

I'm just trying to understand how to achieve/maintain boost with regards to air in the combustion cycle.

This is the wrong way to think about it.

Think about it in stages. hot exhaust gas spools the turbine wheel causing the compressor wheel to produce boost.

Boost is regulated by the actuator or wastegate, it will only allow the turbo to boost a certain psi.

Aftermarket CAI is not worth much in a turbo system, unless the OEM design is done poorly, which most FI BMWs I've seen aren't. Sure, to the guy selling you the system, they are worth a lot of cash in pocket, so don't believe to much they tell you. If you want more power, get a well-designed bigger intercooler and manage boost levels throughout the rev range. Of course, many things can be done which all add up, but I think that we need to stick to the scope of the topic here.


I agree and disagree with this statement. It all depends on the design on the CAI. I will go over CAI's in the thread though

 

[Crash_Nemesis]

BURGY IS A TURBO YODA!

[video=youtube]

---

Granted that is a Supercharger in the video... same difference. Ha ha.. This is the Force Induction Explained thread...

 

[Burgy]

:biglol:

Omg thats funny

 

[petrivanzyl]

According to wikipedia the effect of temperature on air density is as follows:

°C 	 	Density of air ρ in kg·m−3
+35 	 	1.1455
+30 	 	1.1644
+25 	 	1.1839
+20 	 	1.2041
+15 	 	1.2250
+10 	 	1.2466
 +5 	      1.2690
 +0 	 	 1.2922

http://en.wikipedia.org/wiki/Density_of_air

This means for example that there is 10.8% "more" air when it's 5C vs 35C. Right?

So if you could increase the volume of air by 10.8% with the temperature staying the same, the impact would be the same as having the cooler air?

:dunno:

:fencelook:

 

[cOlDFuSiOn]

Would porting the turbo inlet and outlets help performance? Should it result in smoother airflow or are the stock units we get sold already perfectly polished?
Also s per Petri's comment an increase in density means a direct increase in pressure right? So the cooler it runs it would be equivent to running (slightly) higher boost? A gazillion questions from the newby here.. :fencelook:

 

[Burgy]

Would porting the turbo inlet and outlets help performance? Should it result in smoother airflow or are the stock units we get sold already perfectly polished?
Also s per Petri's comment an increase in density means a direct increase in pressure right? So the cooler it runs it would be equivent to running (slightly) higher boost? A gazillion questions from the newby here.. :fencelook:

It all depends on the turbo, and all depends on how much is 'polished'.

To explain this theory, take a straw, blow through it, then take a 3" pipe and blow through it.

This has to do with air veloicy vs air pressure.

There is a direct relationship between air temperature and air density.

All things being equal, you will achieve slightly higher boost in colder denser air, but since boost pressure is regulated by the actuator or wastegate, you will still achieve the same top boost

feel free to ask!

 

[Mo35]

Log the car and see how the compressor is working, if its working harder you have the wrong intake. DCIs suck in more volumetric air hence less strain on the compressor. Read N54 tests