[OpenFlash]

Background
There has been a lot of talk on what is the maximum safe boost pressure that one can run on the N54 motor. Sounds like a simple question until we look at the reality of the situation. And that is what this post is going to attempt to reveal.

Boost pressure, by itself, is surprisingly noncritical measurement. If you think about it, boost pressure is simply the measure of how air pressure is in the intake manifold. Basically, it's an instantaneous one dimensional measurement of the air that isn't going into the engine. What we really want to know is maximum safe ENGINE LOAD. To get an indication of actual engine load, and how much load is "safe", we need to dig a lot deeper.

First, what is Engine Load and why do we care about it?
Engine load can be quantified by just how many oxygen molecules are consumed, at any given time, by the engine. It's these oxygen molecules, when combined with fuel, pressure and a properly timed spark, that combust and provide power. The more oxygen molecules in there, the more engine load, the potent the combustion and the greater the engine output (all other things equal, of course). Defining maximum engine load is important to determine just how much power an engine can generate, given constraints, without "breaking"

Contrary to popular belief, Engine load is NOT manifold pressure/boost. This is because it is possible to keep manifold pressure constant while greatly change actual engine load. One way of doing this is dropping the manifold air temp. This can be done through running a more efficient intercooler or even driving on a cooler night. If the pressurized air charge in the intake manifold is cooler, it is also denser. Cooler/denser air has more oxygen molecules than warmer/less dense air. As such, each resultant engine combustion will generate more energy and more engine load.

Another way to drastically change engine load while keeping manifold pressure/boost constant is to introduce nitrous oxide (N2O) into the manifold. Nitrous oxide is a compressible liquid that breaks down in a gas when subject to temp and pressure. While doing so, it releases gobs of burnable oxygen and increases engine loading in a big way. There are also huge cooling effects provided by nitrous oxide (from the vaporization from liquid to gas) that make the air charge in the combustion change even denser! It's a double whammy when it comes to engine load and power output.

Yet another way to influence engine load while keeping manifold pressure constant is to adjust valve/cam timing. The latter while have massive influence over how much air actually makes it way into the combustion changer. In the case of the N54, valve timing is continually changed as a function of throttle angle, temp, rpm, manifold pressure, etc,.

So, by now, it should be fairly obvious why boost pressure does not equal engine load. Moving on...


How does the factory ECU measure engine load?
There are two popular ways to measure engine load. One is through a Mass Air Flow (MAF) sensor. And the other, as in the case of the N54 is through a Temperature and Manifoild Absolute Pressure (T-MAP) sensor. Let's just talk about the latter since it applies to our application.
It's interesting note that neither load measuring device actually measures load. Instead, it calculates load based upon 2 or 3 individual sensors. In the case of the N54's T-MAP, it measures both manifold temperature and air pressure. Knowing the temp and the pressure of the air charge allows the ECU to calculate the density of the air in the intake manifold. And, as such, how many oxygen molecules get consumed by the engine per engine event (which is load, once again).

Why does the factory ECU monitor engine load?
One reason the factory ECU needs to accurately calculate engine load in order to deliver appropriate amount of fuel and to initiate the spark at the right time in the combustion cycle. [The addition of a tuning computer, like the PROcede, does influence this part of the game. But that's for another thread.]

The other reason the ECU measures load is to keep the engine operating within its desired output parameters. In the case of the N54, BMW limited power output to 300bhp. It will make close to this power output regardless of changes in operating conditions. If outside temperature goes down, so does the boost temperature (as measured by the T-MAP). Immediately, the ECU compensates for the increased air density by lower the boost pressure slightly. If charge temperatures increase, the ECU anticipates the reducing in air density and bumps up boost slightly. These realtime changes to maximum boost pressure ensures that the engine is making constant power, regardless of ambient temperatures. And by making consistent maximum power, the ECU is also ensuring the fuel system is operating within its desired capacity and that everything is within reasonable given the octane/chemical and hardware/mechanical constraints. This is a very very good thing. [Even more of a good thing when we tune the car to make more power. But more on that in another post.]

What does all this stuff mean?
That the factory ECU is a lot smarter than we give it credit for with regards to controlling power output. It also means not to get so hung up on boost pressure. Yes, monitor it. Either through a boost gauge or through tuning software (if available). But realize that it does not equal engine load which is the real determinator of how much work an engine is doing. Boost will change as a function of charge air temp. Which means:

1) That during a 1st to 4th gear run, you will see more slightly boost in 4th gear than you see in 3rd. Slightly more in 3rd that you see in 2nd. And more in 2nd than you saw in 1st (ignoring throttle closure caused by traction control of course).

2) On hot days, you will see more boost than you do during cool nights.

3) That a good intercooler upgrade will actually lower your boost pressures based upon its ability to cool the air better.

4) If you idle your car for a while (which will increase charge temps due to intercooler heatsoak, heat saturation of ic pipes, etc,.) you will see more boost when you immediately take off and begin a run. Conversely, if you are cruising alone the highway for a while (intercooler and piping is nice and cool), you will see slightly less boost than normal when you jump the throttle. Boost pressure will then rise, during the run, as things get hotter and intake charge increases.


PART 2 coming soon....


.

[Sniz]

good read....thanks

[e90AW335i]

Very informative.....Thanks....

[chris b.]

Originally Posted by Sniz

good read....thanks

+1

[Vyruz Reaper]

thanks for the info

[cn555ic]

good readings

[Ruff Rider]

cant wait for the movie

[DrDomer]

So, if boost increases 3psi, then engine output increases as long as fuel and spark follow? If engine output increases through increasing boost, changing fuel and spark; does heat of the engine increase? What's the number one enemy of a turbo engine? Just trying to learn. Thanks for the help!

[boosted305]

so is this why there seems to be debate regarding an intercooler's value as an upgrade?

From what your saying, the increase in power I may realize from a more efficient intercooler will be offset automatically by the computer lowering the boost....(which blows!! no pun intended)

Does PROCEDE address this automatically compensate for this, i.e. if I get PROCEDE and then add an intercooler...will PROCEDE keep the ECU from dropping the boost so that I can realize the full benefits of the intercooler?

thanks in advance

[2007_E93]

WELL,...I MUST SAY,....

SHIV ought to get SPONSOR OF THE YEAR as far as I'm concerned.

I've NEVER been strongly on one side of the fence as far as Vishnu is concerned and with the complaints of poor customer service etc. But I have to say, NO OTHER SPONSOR or manufacturer has provided such in depth and knowledgeable posts and taken the time to educate those of us that are new to tuning as SHIV and his crew!! Well done. Even if the other tuners possess the knowledge they do not spend time on here educating us as Shiv does. This is excellent customer service in my book. An educated consumer is a better consumer.

Bravo,..Shiv...can't wait for part 2.

[e90AW335i]

Originally Posted by 2007_E93

An educated consumer is a better consumer.

+1

[stillclaimndp]

Awesome info.

Shiv, is the use of T-MAP vs. MAF the reason that my Eclipse would boost higher on cold nights whereas according to this explanation you are indicating the 335i will boost lower on cold nights as it requires less boost to make the same power (assuming stock application) and the T-MAP is better at making consistent power? Or is that more to do with the temperature of the turbo/engine than the monitoring system and ECU?

[scalbert]

Thank you...

[thealbert]

Thanks! Great read! Can't wait for part 2.

[BoostedBMW]

Very interesting read... good post.

I never thought that the car would run less boost when the conditions were better seeing that my last car was just the opposite, but it does make sense since my car always seems to boost a little less after cruising for a while.

[pikkashoe]

Great informative post. Cant wait for part 2.

[jbuds335xi]

Great info, always good to learn a little more about these beasts we whip around in.

[remydlc]

WOW, we needed that. There is a lot of misinformation around here. Thanks Shiv for taking the time, we really appreciate it.

[Orb]

Originally Posted by shiv@vishnu

Background
There has been a lot of talk on what is the maximum safe boost pressure that one can run on the N54 motor. Sounds like a simple question until we look at the reality of the situation. And that is what this post is going to attempt to reveal.

Boost pressure, by itself, is surprisingly noncritical measurement. If you think about it, boost pressure is simply the measure of how air pressure is in the intake manifold. Basically, it's an instantaneous one dimensional measurement of the air that isn't going into the engine. What we really want to know is maximum safe ENGINE LOAD. To get an indication of actual engine load, and how much load is "safe", we need to dig a lot deeper.

First, what is Engine Load and why do we care about it?
Engine load can be quantified by just how many oxygen molecules are consumed, at any given time, by the engine. It's these oxygen molecules, when combined with fuel, pressure and a properly timed spark, that combust and provide power. The more oxygen molecules in there, the more engine load, the potent the combustion and the greater the engine output (all other things equal, of course). Defining maximum engine load is important to determine just how much power an engine can generate, given constraints, without "breaking"

Contrary to popular belief, Engine load is NOT manifold pressure/boost. This is because it is possible to keep manifold pressure constant while greatly change actual engine load. One way of doing this is dropping the manifold air temp. This can be done through running a more efficient intercooler or even driving on a cooler night. If the pressurized air charge in the intake manifold is cooler, it is also denser. Cooler/denser air has more oxygen molecules than warmer/less dense air. As such, each resultant engine combustion will generate more energy and more engine load.

Another way to drastically change engine load while keeping manifold pressure/boost constant is to introduce nitrous oxide (N2O) into the manifold. Nitrous oxide is a compressible liquid that breaks down in a gas when subject to temp and pressure. While doing so, it releases gobs of burnable oxygen and increases engine loading in a big way. There are also huge cooling effects provided by nitrous oxide (from the vaporization from liquid to gas) that make the air charge in the combustion change even denser! It's a double whammy when it comes to engine load and power output.

Yet another way to influence engine load while keeping manifold pressure constant is to adjust valve/cam timing. The latter while have massive influence over how much air actually makes it way into the combustion changer. In the case of the N54, valve timing is continually changed as a function of throttle angle, temp, rpm, manifold pressure, etc,.

So, by now, it should be fairly obvious why boost pressure does not equal engine load. Moving on...


How does the factory ECU measure engine load?
There are two popular ways to measure engine load. One is through a Mass Air Flow (MAF) sensor. And the other, as in the case of the N54 is through a Temperature and Manifoild Absolute Pressure (T-MAP) sensor. Let's just talk about the latter since it applies to our application.
It's interesting note that neither load measuring device actually measures load. Instead, it calculates load based upon 2 or 3 individual sensors. In the case of the N54's T-MAP, it measures both manifold temperature and air pressure. Knowing the temp and the pressure of the air charge allows the ECU to calculate the density of the air in the intake manifold. And, as such, how many oxygen molecules get consumed by the engine per engine event (which is load, once again).

Why does the factory ECU monitor engine load?
One reason the factory ECU needs to accurately calculate engine load in order to deliver appropriate amount of fuel and to initiate the spark at the right time in the combustion cycle. [The addition of a tuning computer, like the PROcede, does influence this part of the game. But that's for another thread.]

The other reason the ECU measures load is to keep the engine operating within its desired output parameters. In the case of the N54, BMW limited power output to 300bhp. It will make close to this power output regardless of changes in operating conditions. If outside temperature goes down, so does the boost temperature (as measured by the T-MAP). Immediately, the ECU compensates for the increased air density by lower the boost pressure slightly. If charge temperatures increase, the ECU anticipates the reducing in air density and bumps up boost slightly. These realtime changes to maximum boost pressure ensures that the engine is making constant power, regardless of ambient temperatures. And by making consistent maximum power, the ECU is also ensuring the fuel system is operating within its desired capacity and that everything is within reasonable given the octane/chemical and hardware/mechanical constraints. This is a very very good thing. [Even more of a good thing when we tune the car to make more power. But more on that in another post.]

What does all this stuff mean?
That the factory ECU is a lot smarter than we give it credit for with regards to controlling power output. It also means not to get so hung up on boost pressure. Yes, monitor it. Either through a boost gauge or through tuning software (if available). But realize that it does not equal engine load which is the real determinator of how much work an engine is doing. Boost will change as a function of charge air temp. Which means:

1) That during a 1st to 4th gear run, you will see more slightly boost in 4th gear than you see in 3rd. Slightly more in 3rd that you see in 2nd. And more in 2nd than you saw in 1st (ignoring throttle closure caused by traction control of course).

2) On hot days, you will see more boost than you do during cool nights.

3) That a good intercooler upgrade will actually lower your boost pressures based upon its ability to cool the air better.

4) If you idle your car for a while (which will increase charge temps due to intercooler heatsoak, heat saturation of ic pipes, etc,.) you will see more boost when you immediately take off and begin a run. Conversely, if you are cruising alone the highway for a while (intercooler and piping is nice and cool), you will see slightly less boost than normal when you jump the throttle. Boost pressure will then rise, during the run, as things get hotter and intake charge increases.


PART 2 coming soon....


.

You do mean estimate? You need RPM or something else to rationalize.

"Knowing the temp and the pressure of the air charge allows the ECU to calculate the density of the air"

Orb

[Ado]

^^
IGNORE IT.

I can honestly say that I know much more about the 335 engine then I did a few minutes ago. Shiv thanks for the info, it's much appreciated. I'm happy that someone this knowledgeable is working on tuning the 335's.

[lawdude]

Originally Posted by KenB

Some of you ass kissers make me sick

Ass kisser neither validate nor invalidate the info. What's your best technical analysis of the info?

[tibbz]

interesting ready....thanks shiv