[OpenFlash]

Originally Posted by e.n335

... I've seen videos where boost responded directly to pedal position. While it looks cool, it might be really hard to the turbos and fuel-system, IMO.

While I appreciate your opinion, let's talk facts. The reason that v4 boost responds directly and immediate to throttle position has nothing to with how quickly we increase the rate of turbo shaft rotation. That rate of rotational acceleration is limited by the inertia of the shaft/wheels and by the amount of motive force we apply on it (the turbine wheel specifically) by the exhaust flow. We can't decrease the former or increase the latter.

The reason the boost responds so immediately and accurately has to do with the fact that we know exactly where the actual throttle blade is positioned at all times. So we never induce a very commonly experienced situation where the turbos are asked to blow against a closed (or partially closed) throttle blade. Needless to say, this is actually is far more stressful on the thrust bearings of the turbos than anything that we could possibly to do them ourselves.

With a little research you may find that with v4, pre and post throttle boost pressure are almost always the same. This is because the DME is rarely forced to close throttle when reacting to a perceived overboost condition. You will also find that turbo wastegate DC, as an average is lower with v4, than it is with other tunes that run the same boost. Again, this is because we are not forcing the turbo to push against things (half opened throttle blades, for instance) that it doesn't naturally want to push through.

And secondly, if a fuel injector that is designed to pulse several injections per engine event, can't react quickly to load changes that are caused by a someone large spinning wheel that has a thousands of times more inertia than the piezoelectric mechanism in the injector, someone screwed up.

And lastly, one you experience what it is like to drive a turbo system that is properly optimized for response, there's no going back. It's easier and more fun to drive. And you can also run less boost and achieve the same amount of general performance.

my 2c,
Shiv

[Prince ///M]

Could you please better explain the concept on the stress induced by partial throttle closure?

In particular, at the same engine rpm and pressure in front of throttle valve, which turbo wheel is rotating faster?

A) the one with 100% valve opening

B) the one with 50% valve opening

[zsapphire7]

I think u can imagine it this way, if theres throttle closure, essentially the turbos will be spinning into a closed system/space. Its like blowing into a closed cup with a straw trying to maintain pressure. Youll feel the strain in ur cheeks. If theres a hole now in that cup, throttle wide open, then your stressed less even tho you push through more air. Turbos will spin but not be strained from backpressure?

[e.n335]

Originally Posted by shiv@vishnu

While I appreciate your opinion, let's talk facts. The reason that v4 boost responds directly and immediate to throttle position has nothing to with how quickly we increase the rate of turbo shaft rotation. That rate of rotational acceleration is limited by the inertia of the shaft/wheels and by the amount of motive force we apply on it (the turbine wheel specifically) by the exhaust flow. We can't decrease the former or increase the latter.

The reason the boost responds so immediately and accurately has to do with the fact that we know exactly where the actual throttle blade is positioned at all times. So we never induce a very commonly experienced situation where the turbos are asked to blow against a closed (or partially closed) throttle blade. Needless to say, this is actually is far more stressful on the thrust bearings of the turbos than anything that we could possibly to do them ourselves.

With a little research you may find that with v4, pre and post throttle boost pressure are almost always the same. This is because the DME is rarely forced to close throttle when reacting to a perceived overboost condition. You will also find that turbo wastegate DC, as an average is lower with v4, than it is with other tunes that run the same boost. Again, this is because we are not forcing the turbo to push against things (half opened throttle blades, for instance) that it doesn't naturally want to push through.

And secondly, if a fuel injector that is designed to pulse several injections per engine event, can't react quickly to load changes that are caused by a someone large spinning wheel that has a thousands of times more inertia than the piezoelectric mechanism in the injector, someone screwed up.

And lastly, one you experience what it is like to drive a turbo system that is properly optimized for response, there's no going back. It's easier and more fun to drive. And you can also run less boost and achieve the same amount of general performance.

my 2c,
Shiv

Shiv,

Please PM your email address where I can send a BT log (excel) with AT shifts on WOT. From my flashed car.

Eugen

[A418t81]

A turbo spinning at 100k rpm may generate 10 psi at WOT. 13-14 psi against the pressure side of the blade at the exact same compressor rpm against a throttle plate 50% open. There's a bit more force on the CHRA and shaft just from the higher pressure against the wheel, but nothing that would wear thrust collars or the bearings. Thrust collars are worn out by axial loading, typically from being spun to high enough rpm that the effective balancing becomes a bit suspect which allows fore/aft movement of the rotational assembly from the vibration induced...most occurs when the turbo is hung out, a full 360 deg collar isn't used, and frankly, the turbo isn't especially well put together and has a bit of excessive play. The fore/aft movement is also, obviously, an issue for the dynamic bearing and it's seals as well.

Edit: I almost completely reworded my post as I obviously did not manage it put into coherent english what I was trying to get across...it's been a long day at work

[adrian@vishnu]

Originally Posted by shiv@vishnu

While I appreciate your opinion, let's talk facts. The reason that v4 boost responds directly and immediate to throttle position has nothing to with how quickly we increase the rate of turbo shaft rotation. That rate of rotational acceleration is limited by the inertia of the shaft/wheels and by the amount of motive force we apply on it (the turbine wheel specifically) by the exhaust flow. We can't decrease the former or increase the latter.

The reason the boost responds so immediately and accurately has to do with the fact that we know exactly where the actual throttle blade is positioned at all times. So we never induce a very commonly experienced situation where the turbos are asked to blow against a closed (or partially closed) throttle blade. Needless to say, this is actually is far more stressful on the thrust bearings of the turbos than anything that we could possibly to do them ourselves.

With a little research you may find that with v4, pre and post throttle boost pressure are almost always the same. This is because the DME is rarely forced to close throttle when reacting to a perceived overboost condition. You will also find that turbo wastegate DC, as an average is lower with v4, than it is with other tunes that run the same boost. Again, this is because we are not forcing the turbo to push against things (half opened throttle blades, for instance) that it doesn't naturally want to push through.

And secondly, if a fuel injector that is designed to pulse several injections per engine event, can't react quickly to load changes that are caused by a someone large spinning wheel that has a thousands of times more inertia than the piezoelectric mechanism in the injector, someone screwed up.

And lastly, one you experience what it is like to drive a turbo system that is properly optimized for response, there's no going back. It's easier and more fun to drive. And you can also run less boost and achieve the same amount of general performance.

my 2c,
Shiv

e.n355,

Where do you get your knowledge on turbo vehicles? Have you worked on them before? Do you know about injection systems. Statements such as this show a lack of knowledge, and in a public forum show a desire to derail a product by creating doubt and confusion.

There is absolutely no extra stress on the fuel system. It operates at pressures MANY times great than boost pressure (like 100s times) and much greater than combustion pressure. The small change in boost would not even be in any way noticable to the fuel system. The Procede controls fuel pressure independantly of boost. It is more stressful on the pump to run continuous high boost which will be on average lower with V4.

As for the turbo, in terms of acceleration and decleration of the turbine, the most deceleration of the turbine is in the situation that Shiv mentioned... closing the throttle. This is why BMW put the BOVs in there... to reduce this deceleration which can effect turbo service life. In terms of acceleration of the turbo... well most turbo engines ran wastegates that are fully closed until the actuator pressure. So until you reach that the turbo acceleration is only limitted by the inertia of it and the air. In V4, we have that limit also. It is generally recognised that you cannot over accelerate a turbo. Manufacturers strive for minimum lag which mean they accelerate it as much as possible. The worst case acceleration is going from (at high RPM) min boost to max boost. By nature, the adjustable boost point with throttle on V4 will actually reduce occurances of this, as the driver will more often go for lower boosts since they now have more control. So instead of going low speed to max speed, you are more likely to go from low/medium speed to high/medium speed in most driving.

Adrian

[Prince ///M]

Originally Posted by A418t81

A turbo spinning at 100k rpm with a throttle plate may generate 10 psi at WOT. Against a throttle plate 50% open, 13-14 psi against the pressure side at the exact same rpm. There's a bit more force on the CHRA and shaft, but nothing that would wear thrust collars or the bearings. Thrust collars are worn out by axial loading, typically from being spun to high enough rpm that the effective balancing becomes a bit suspect which allows fore/aft movement of the rotational assembly from the vibration induced...most occurs when the turbo is hung out, a full 360 deg collar isn't used, and frankly, the turbo isn't especially well put together with excessive play. The fore/aft movement is also, obviously, an issue for the dynamic bearing and it's seals as well.

one little piece of information in order to help answering my question...

The throttle blade in the n54 is used as part of TORQUE control so that if the actual pressure BEFORE the throttle itself exceeds (by a minimal amount) the target, a (relatively slow) closure is induced keeping the same boost level with simultaneous reduction of wastegates dc.

So I ask again: with the SAME boost level, which turbo wheel is more stressed?

A) 100% throttle opening

B) 50% trottle opening

[OpenFlash]

Originally Posted by Prince ///M

Could you please better explain the concept on the stress induced by partial throttle closure?

In particular, at the same engine rpm and pressure in front of throttle valve, which turbo wheel is rotating faster?

A) the one with 100% valve opening

B) the one with 50% valve opening

If you hold other things constant (manifold pressure, engine torque output, etc,.), the turbo pushing against the half closed throttle is spinning faster. This is because it has to make up for the pressure loss that the TB is inducing.

But if you are assuming we hold the TMAP pressure equal, then the other turbo will likely be spinning slower because it's pushing against an engine with reduced pumping efficiency. But the engine (and the driver) doesn't care about TMAP pressure. That's just a measurement of the air that doesn't get into the engine. We only really care about the manifold pressure (downstream of the throttle body.)

Shiv

[Prince ///M]

Originally Posted by shiv@vishnu

If you hold other things constant (manifold pressure, engine torque output, etc,.), the turbo pushing against the half closed throttle is spinning faster. This is because it has to make up for the pressure loss that the TB is inducing.

Shiv

For sure, if you want to keep the torque at constant level with more restictive passage through the valve you need to spin faster the turbo (higher pressure ratio with the same mass flow).

But this is not the case we are considering here.

The controlled value is the boost level (I repeat) BEFORE throttle valve and a closure of the latter happens for the sole purpose of torque REDUCTION.

So...

[OpenFlash]

Originally Posted by Prince ///M

For sure, if you want to keep the torque at constant level with more restictive passage through the valve you need to spin faster the turbo (higher pressure ratio with the same mass flow).

But this is not the case we are considering here.

The controlled value is the boost level (I repeat) BEFORE throttle valve and a closure of the latter happens for the sole purpose of torque REDUCTION.

So...

I'm really not sure what your point is. But my point is that you can make power the same power in two different ways. Spinning the turbo faster and blowing through a less open throttle blade. Or spinning it slower and blowing through a more open throttle blade. V4 is characterized by the latter. And datalogs (not to mention seat of the pants driving experience) will support this.

Shiv

[Prince ///M]

My point is quite simple:
all the tunes I analysed (giac,jb3,Aa,stock tune, power kit, provede v3) cause some degrees of throttle closure but keeping constant pressure in front of throttle valve (the only measured one... also for v4).

So, if you set a target of 14psi for such 'flawed' systems and the same level for v4, the result will be the following:
better performance on v4 because of less closure but more stress on the turbo wheels.

In other words...
A jb3 at 14psi is (probably) slower than V4 at 14psi, but do not involve more risks for the engine... beside lack of timing control .

[scalbert]

Originally Posted by A418t81

Edit: I almost completely reworded my post as I obviously did not manage it put into coherent english what I was trying to get across...it's been a long day at work

So, you didn't disappear into the Corvette world? Needed a little does of this crazy world.

[A418t81]

Originally Posted by scalbert

So, you didn't disappear into the Corvette world? Needed a little does of this crazy world.

Bah, I don't like the corvette forums...its a bunch of old guys showing off their latest ricer mods (air brushed corvette flags on anything you can possibly imagine, along with making anything your heart desires chrome under the hood)

Frankly turbo systems are more complex and much more interesting from a technical standpoint. There's really only so much arguing you can do over LSA, duration, and lift before its boring.

As for the car, I freaking love it. Simple, to the point, and ohmigod the power of this thing. I only trapped 123.x when I ran it, but on the street if you aren't every bit of a 130 mph vehicle, you'd better watch out

[GeorgiaTech335coupe]

Originally Posted by A418t81

Bah, I don't like the corvette forums...its a bunch of old guys showing off their latest ricer mods (air brushed corvette flags on anything you can possibly imagine, along with making anything your heart desires chrome under the hood)

Frankly turbo systems are more complex and much more interesting from a technical standpoint. There's really only so much arguing you can do over LSA, duration, and lift before its boring.

As for the car, I freaking love it. Simple, to the point, and ohmigod the power of this thing. I only trapped 123.x when I ran it, but on the street if you aren't every bit of a 130 mph vehicle, you'd better watch out

What? You don't like being on the corvette forum and talking tech to guys like the one is this video?

**************************car-videos-09...35&PID=3147428

[Sniz]

Originally Posted by GeorgiaTech335coupe

What? You don't like being on the corvette forum and talking tech to guys like the one is this video?

**************************car-videos-09...35&PID=3147428

that is too funny lol

reminds me of the guy driving an e60 M5 at one of our MIR rentals that thought he was doing a burnout, turns out he was frying his DCT tranny

[wsybert]

Originally Posted by GeorgiaTech335coupe

What? You don't like being on the corvette forum and talking tech to guys like the one is this video?

**************************car-videos-09...35&PID=3147428

OMG... that is too damn funny.

[blisstik]

I like how the camera man said "that was not the tires".... LOL!

[vase330]

Originally Posted by GeorgiaTech335coupe

What? You don't like being on the corvette forum and talking tech to guys like the one is this video?

**************************car-videos-09...35&PID=3147428

obviously I have no words to describe that shit. How do you even do that? Wait, I don't want to know. "Bye bye $600", he obviously forgot the extra 0 at the end of that number jeez!

[marconi118]

Shiv,
Do you use the TMAP before throttle plate or the MAP in the manifold to regulate the boost (PID) ?


It makes a difference in case of partial plate closure