[e.n335]

Hi,

I use the AA Active Processor and had the chance to drive my car yesterday quite some time on the Autobahn. What I realized is that the AA tuning tapers down boost to ~ 8.5 psi @ redline. BTW, max. boost without the spikes that occur during shifting has been 13.0 psi, with the spikes it has been 13.5 psi ( not seen by the engine ). This is for Steptronic trannies. Ambient temperature has been 60 degF, gas is Shell V-power 95.5 AKI ( 100 octane RON ). The car is pretty fast .

Now, some of the tunings taper down boost, some don't. My question is what are the rationals behind this boost tapering down ?

Any feedback appreciated.

Cheers,
Eugen

[OpenFlash]

Originally Posted by e.n335

Hi,

I use the AA Active Processor and had the chance to drive my car yesterday quite some time on the Autobahn. What I realized is that the AA tuning tapers down boost to ~ 8.5 psi @ redline. BTW, max. boost without the spikes that occur during shifting has been 13.0 psi, with the spikes it has been 13.5 psi ( not seen by the engine ). This is for Steptronic trannies. Ambient temperature has been 60 degF, gas is Shell V-power 95.5 AKI ( 100 octane RON ). The car is pretty fast .

Now, some of the tunings taper down boost, some don't. My question is what are the rationals behind this boost tapering down ?

Any feedback appreciated.

Cheers,
Eugen

How are you measuring boost?

[e.n335]

Digital boost gauge ( High-res VEI Systems ). Same VAC/BOOST connection like most of us near the DV's. The gauge stores peak boost, so it's easy to tell the peak values. Altitude has been between 900 - 1800 ft.

[OpenFlash]

Originally Posted by e.n335

Digital boost gauge ( VEI Systems ). Same VAC/BOOST connection like most of us near the DV's.

That boost source comes right from the intake manifold. Why do you say that your engine isn't seeing those boost spikes during shifts? Only if you were datalogging and measuring the TMAP sensor which is in the intercooler pipe, you're statement would be true.

shiv

[e.n335]

Originally Posted by shiv@vishnu

That boost source comes right from the intake manifold. Why do you say that your engine isn't seeing those boost spikes during shifts?

shiv

My bad. I guessed this boost source measures boost before the throttle valve as well. Thank you for clarification. What about this boost tapering down thing, Shiv ?

[OpenFlash]

Originally Posted by e.n335

My bad. I guessed this boost source measures boost before the throttle valve as well.

Yes. And as someone who readily offers his opinion regarding the boost control performance of different tuning systems, you really should understand this by now. I don't mean to be hard on you Eugen but you're misunderstandings regarding this subject have caused a lot of confusion. People look to you for your opinion and you really need to get your facts together before you give it.

There are a number of possible reasons for the big boost drop. The question is, is there a solenoid bypass (physical or electrical) involved with your current set-up?

Shiv

[e.n335]

Originally Posted by shiv@vishnu

Yes. And as someone who readily offers his opinion regarding the boost control performance of different tuning systems, you should understand this by now.

There are a number of possible reasons for the big boost drop. The question is, is there a solenoid bypass (physical or electrical) involved with your current set-up.

Shiv

Well understood now. There is a physical solenoid bypass, but AFAIK the Dinan ECU flash tapers down boost as well ...

[e.n335]

Originally Posted by shiv@vishnu

Yes. And as someone who readily offers his opinion regarding the boost control performance of different tuning systems, you really should understand this by now. I don't mean to be hard on you Eugen but you're misunderstandings regarding this subject have caused a lot of confusion. People look to you for your opinion and you really need to get your facts together before you give it.

There are a number of possible reasons for the big boost drop. The question is, is there a solenoid bypass (physical or electrical) involved with your current set-up?

Shiv

UUPS, you edited your posting. I'm not here to fight against Vishnu, Shiv, I asked a question. When you chime in, I guess you like to offer your help. As a moderator of this forum I have to show appropriate respect to commercial sponsors.

[ybbiz34]

In a nutshell, I think tapering down boost at high rpms saves the little turbos. I could be wrong.

"Increased boost pressure exceeds the turbochargers’ design limitations at higher rpm, potentially shortening their lifespan. [Tapering boost] also addresses the fact that with increased boost at higher rpm the turbocharger temperatures would exceed the intercooler’s ability to cool the intake charge, resulting in a loss of power and compromising the long-term durability of the engine."

[e.n335]

Originally Posted by ybbiz34

In a nutshell, I think tapering down boost at high rpms saves the little turbos. I could be wrong.

"Increased boost pressure exceeds the turbochargers’ design limitations at higher rpm, potentially shortening their lifespan. [Tapering boost] also addresses the fact that with increased boost at higher rpm the turbocharger temperatures would exceed the intercooler’s ability to cool the intake charge, resulting in a loss of power and compromising the long-term durability of the engine."

Thanks for the explanation, who is the author of the information you refer to ?

[ybbiz34]

Originally Posted by e.n335

Thanks for the explanation, who is the author of the information you refer to ?

You are most welcome. Dinan.

[5soko]

yea i hope all tunes will tapers boost down.
ybbiz you beat me to it.

[OpenFlash]

Originally Posted by e.n335

Well understood now. There is a physical solenoid bypass, but AFAIK the Dinan ECU flash tapers down boost as well ...

By the sounds of it, I'll explain how your set-up's boost control system is working. By the sounds of it, it works exactly the same way as our v1 PROcede set-up. As such, I can only assume the same limitations apply. If I'm wrong, perhaps AA can jump in and clarify.

The stock car is designed to run 6-8psi of boost, taper off to 2-3psi just before the rev limit. But while doing so, it expects to keep boost control duty cycle within a certain range. For the sake of explanation, let's just say that this range is between 40 to 60%. The more Duty Cycle % (DC%), the more boost. If the Duty cycle required to acheive the boost target goes above the upper limit (60%), the ECU will induce a limp mode and throw a BMW specific code for 'boost too low'. Meaning that it feels that it is working too hard to make the desired boost and it will conclude that either the turbos are failing or, more likely, that there is a boost leak somewhere. If the required DC% to achieve the boost target is below the lower end of the range (20%), the ECU will induce a limp and throw a code for boost too high. It will think that it was "too easy" to hit the boost target and that something must be wrong with the wastegate actuator.

Luckily for the stock car, the allowable DC% range is wide enough that it's virtually impossible to fall outside this range when hitting the factory boost target, regardless of altitude, temp, mechanical variance in turbos, etc,.

But now we start tuning. The most simple way (what we did with v1 and what most others are still doing) is as follows:

To raise boost, they trim back the TMAP sensor voltage. Passive devices like the JB does this by using 2 resistors configured as a voltage divider. Computers such as the PROcede v1, Xede, AA processor, Helix, etc,. do this by taking in the TMAP signal, processing it and outputting a recreated/reduced TMAP signal to the factory ECU.

With the trimmed TMAP signal, the ECU thinks it is running less boost than it really is. As such, it responds by increasing duty cycle. The allowable DC range is wide enough to get away with 12-13psi, tapering off to 8-10psi by redline. in *most* conditions. In extreme heat, altitude, etc, things may get sketchy and induce the 'boost too low' code/limp discusssed above. So in order to get more boost, without driving the solenoids directly (and getting around this DC range limitation), one needs to effectively bring DC% up without actually making the ECU drive the solenoids harder. This is where the solenoid bypass comes in. With one solenoid bypassed (either electrically ie Helix or physically ie AA, JB, PROcede v1), it effectively behaves like it is running 100% duty cycle. This raises total "effective" duty cycle of the two solenoids up by a bit. So now the system is capable of supporting 13-15psi, tapering off to 10-11psi by redline while still operating within its allowable DC% range.

In the case of the 6AT, things get a little bit trickier. During the last 500rpm before redline, the throttle begins to close in preparation for the upshift. When this throttle closes, pressure builds up in the intercooler pipe (where the TMAP is). As such, the ECU sees this high boost and starts to react by dropping DC%. If the DC% goes below the min allowable value, it will throw a 'boost too high' code. So the only way to reliably avoid it while still using the basic form of boost control described here, is to drop boost even more at high rpm. This is why boost falls to just 8.5psi up top. Any more and 6AT users would be teetering between those two limp-inducing diagnostic codes.

Contrary to what others tuners may suggest, this high RPM boost taper has little to do with turbo longevity/capacity. It's just that running more boost requires a more sophisticated boost control system. Even with respect to reflashing, you will need to get not only access to the max allowable DC range but also all the PID (Proportional, Integral and Derivative) parameters, boost setpoint values, etc,. in order to run the desired boost levels with good boost response. I suspect this is why the current flash from Dinan doesn't have the low end and post-shift boost response than people were expecting. There is also a related reason by boost control systems inolving solenoid bypasses are more prone to boost oscillations/instability during WOT shifting and at low end WOT (when the boost control system is in "full attack/max response" mode). This is because such systems defeat the ability of one solenoid to "catch" boost as it quickly comes up on its boot target. So you are only relying on the influence of one (instead of 2) solenoid. The result is an overboost, followed by a negative correction, followed by a positive correction, etc,. This issue is also compounded by the fact that the factory closed loop PID parameters, which were designed for a 6-8psi system aren't ideal for higher boost scenarios. And the issue gets a lot worse if you are running with fewer (or no) cats. If I misrepresented any product, my apologies. But I am quite familiar with how the boost control works on the stock car. As well as the merits/demerits of the solenoid bypass (which we were the first to do) I welcome other vendors to contribute to this thread.

Cheers,
shiv

[cn555ic]

....I also have a VEI digital gauge and Procede 2-26 map...I did a WOT from 2 to 3rd and couldn't get to fourth because of traffic....I saw boost steady at 14.3-14.7....But on my boost peak recall I saw 16.6...It had to be when I let off the throttle....I thought this psi wasn't seen by the engine...I have the guage hooked up between the diverter valve...Shiv can you chime in because I thought 16.6 wasn't seen by the engine, and your post just contradicted what I thought and what I have read???? Please advise...thank you

[RiXst3r]

Tapering boost at high RPM's is also required for piggybacks that use the solenoid bypass because they will run out of headroom on the solenoid duty cycles without direct solenoid control... I think shiv was hinting at this as well...

oops, just saw he beat me to it

[cn555ic]

Can anyone explain my peak boost recall of 16.6!!

[RiXst3r]

Originally Posted by cn555ic

....I also have a VEI digital gauge and Procede 2-26 map...I did a WOT from 2 to 3rd and couldn't get to fourth because of traffic....I saw boost steady at 14.3-14.7....But on my boost peak recall I saw 16.6...It had to be when I let off the throttle....I thought this psi wasn't seen by the engine...I have the guage hooked up between the diverter valve...Shiv can you chime in because I thought 16.6 wasn't seen by the engine, and your post just contradicted what I thought and what I have read???? Please advise...thank you

I hope shiv chimes in on this one, but my guess is that the boost control system just isnt quick enough to catch a 2psi spike during a shift, which is when it probably happened...

When you have turbos spinning fast enough to provide boost to an engine running at high rpm, when all the sudden you upshift, the wastegates need to react to let out some of the extra boost. The DV's don't open during shifts on the AT from what I can hear/see... and 16psi for a split second is not that bad of a spike IMHO...

Maybe v3 is your answer?

[cn555ic]

Well I remember him saying that at shifts there are spikes and no seen by the engine, then he states that the spikes are seen by the engine if the guage is near the manifold...Isn't that where most people put there guage tubing near the manifold??

Shiv quoted:That boost source comes right from the intake manifold. Why do you say that your engine isn't seeing those boost spikes during shifts? Only if you were datalogging and measuring the TMAP sensor which is in the intercooler pipe, you're statement would be true.

shiv

[OpenFlash]

Originally Posted by cn555ic

Can anyone explain my peak boost recall of 16.6!!

If you are running with 1 or both sets of cats removed, it's very easy to induce a post-shift boost spike. If you are reading it from a boost gauge teed into your bypass valve signal line, it is indeed coming from your manifold and is seen by your engine. It will be very momentary and too quick for you to even see it realtime on a digital gauge. But a peak hold record will catch it. The reason for this is due to the fact that you are running factory PID parameters at 15psi. If you drop boost to 13psi, you'd be hard pressed to catch more than 1psi spike. The spike you describe is not going to cause any problem for you. Although it is what we've set out to address with v3 (which revamps the entire closed loop control system). FWIW, I've measured 4-5psi boost spikes (!) with severe oscillation on solenoid bypassed systems on my full catless/intake car on a cold night. Now, THAT's not good.

Shiv

[RiXst3r]

Originally Posted by cn555ic

Well I remember him saying that at shifts there are spikes and no seen by the engine, then he states that the spikes are seen by the engine if the guage is near the manifold...Isn't that where most people put there guage tubing near the manifold??

Shiv quoted:That boost source comes right from the intake manifold. Why do you say that your engine isn't seeing those boost spikes during shifts? Only if you were datalogging and measuring the TMAP sensor which is in the intercooler pipe, you're statement would be true.

shiv

Procede logs boost from the T-map... which sees spikes more like 20+ psi during throttle closure.

You boost gauge is in the correct place, you want to see what the engine see's.

[cn555ic]

Originally Posted by shiv@vishnu

If you are running with 1 or both sets of cats removed, it's very easy to induce a post-shift boost spike. It will be very momentary and too quick for you to even see it realtime on a digital gauge. But a peak hold record will catch it. The reason for this is due to the fact that you are running factory PID parameters at 15psi. This is what we've set out to address with v3 (which revamps the entire closed loop control system).

Shiv

Yeah SHiv I have the sec cat deleted, but do I have anything to worry about with the 16.6 peak measuring from the lines of the diverter valves...Should I lower my torque settings of 92% for the meantime until I get the V2.1 upgrade??? Thanks shiv

[cn555ic]

Originally Posted by RiXst3r

Procede logs boost from the T-map... which sees spikes more like 20+ psi during throttle closure.

You boost gauge is in the correct place, you want to see what the engine see's.

Yeah I know Rick, but the engine seeing 16.6 can't be good either, even though its for a split second right??