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Rick
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« on: September 03, 2010, 12:21:14 PM »
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How is this acheived? From what I can gather, the max load is 190% which will request around 1.5 bar? Plus the MAP sensor cannot read more than 2.5 bar absolute. For ignition and fuel you would have to tune the top line for the to get the values you want, but how do you get the boost in the first place?
Rick
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Tony@NefMoto
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« Reply #1 on: September 03, 2010, 01:45:53 PM »
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The way most tuners deal with boost above 2550mbar is by manually tweaking the N75 linearization table. Since the MAP sensor can't read above 2550mbar, it is not possible for the ECU to properly control the boost pressure with the PID controller. You can tweak the N75 linearization table to give you custom N75 duty cycles at particular RPMs.
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hammersword
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« Reply #2 on: September 06, 2010, 07:03:18 AM »
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Touching the N75 linearization table you will make the PID controler to open loop condition
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kelesha
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« Reply #3 on: September 06, 2010, 10:54:28 AM »
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Touching the N75 linearization table you will make the PID controler to open loop condition
So you mean that if you change even one value in KFLDRL then PID controller start to work in open loop with fixed duty ? |
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Tony@NefMoto
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« Reply #4 on: September 06, 2010, 11:52:04 AM »
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My stock 2001.5 Audi S4 ECU has an N75 linearization table that has non-normalized values in every cell.
I wouldn't say tuning this table will cause the ECU to run the PID controller in open loop, but you do run the risk of unbalancing the PID controller to the point that it no longer works.
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lulu2003
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« Reply #5 on: September 07, 2010, 08:31:57 AM »
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I wouldn't say tuning this table will cause the ECU to run the PID controller in open loop, but you do run the risk of unbalancing the PID controller to the point that it no longer works.
that is my understanding also. |
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NOTORIOUS VR
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« Reply #6 on: September 12, 2010, 08:46:23 AM »
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AFAIK Bosch has a pnp 4 and or even 5 BAR sensor... what about rescaling the MAP values to use one of them?
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Tony@NefMoto
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« Reply #7 on: September 12, 2010, 01:23:37 PM »
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The problem is the code in the ECU is only written to handle up to 2550mbar. So even if you rescale the reading of the signal from the MAP sensor, if can't represent a value larger than 2550. There is no easy way to make the ECU handle a MAP reading larger than 2550mbar.
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iznogoud
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« Reply #8 on: October 10, 2010, 09:46:31 AM »
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I thought that stage 3 B5 S4s who run that high boost have a hardwired (open loop) N75 duty cycle at WOT.
In partial throttle there is still PID control, correct?
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« Last Edit: October 12, 2010, 11:02:02 AM by Tony@NefMoto »
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Jason
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« Reply #9 on: October 10, 2010, 10:27:48 AM »
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IMO tuning the N75 beyond 1.5 bar is asking for trouble without an MBC in parallel set to your desired peak boost. My car used to be tuned on the N75 alone to peak to 1.7 bar. At altitude the car would hideously overboost and peg my 30PSI gauge. There are probably a few reasons for that based on the tuner's lack of knowledge, but that's another discussion in itself.
I installed an MBC in parallel to clip these spikes - when in parallel, the engine will only make the lowest desired boost that EITHER the N75 or MBC dictates - so you have a safety net, AND the ability to taper the boost.
I am running just an old school ball and spring MBC now without the N75 at all, and I actually prefer it because the boost builds faster - however without a programmable electronic boost controller, you can't spike and taper your boost.
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Rick
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« Reply #10 on: October 10, 2010, 12:44:06 PM »
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An EBC works differently to the N75. The N75 bleeds air away from the wastegate, higher duty cycle means higher boost. An EBC prevents air from going to the wastegate, more duty cycle equals less boost. EBC gives a quicker response because the wastegate doesn't see any pressure until the desired boost is reached, keeping it shut for longer.
I don't think you could use an EBC in // with the N75.
Rick
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iznogoud
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« Reply #11 on: October 10, 2010, 04:28:08 PM »
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I installed an MBC in parallel to clip these spikes - when in parallel, the engine will only make the lowest desired boost that EITHER the N75 or MBC dictates - so you have a safety net, AND the ability to taper the boost.
On stock and stage 1 and 2 S4s, if the MBC caps boost at a lower setting than requested boost and that condition persists while driving, the car thinks that it has a boost leak and will go into limp mode, where there is no N75 regulation -- and the appropriate negative pressure deviation code will be set with no CEL. It happens to me all the time. I have an MBC in parallel to the N75 because I have a tweaked out GIAC tune that likes to overboost while building boost. Somebody played with the PID settings, as I understand it. With an MBC you can max boost or anything in between according to how the load affects the boost calculation based on pedal position. No tapering is possible there by mechanical means. I know somebody who runs an EBC and tehre is no N75 in the game. |
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« Last Edit: October 12, 2010, 10:59:41 AM by Tony@NefMoto »
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Rick
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« Reply #12 on: October 11, 2010, 04:42:08 AM »
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That is because to run a seperate boost controller, you need alter the map for maximum allowed pressure deviation.
Rick
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Jason
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« Reply #13 on: October 11, 2010, 09:01:42 AM »
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On stock and stage 1 and 2 S4s, if the MBC caps boost at a lower setting than requested boost and that condition persists while driving, the car thinks that it has a boost leak and will go into limp mode, where there is no N75 regulation -- and the appropriate negative pressure deviation code will be set with no CEL. It happens to me all the time. I have an MBC in parallel to the N75 because I have a tweaked out GIAC tune that likes to overboost while building boost. Somebody played with the PID settings, as I understand it.
This occurs because your MBC is likely set less than 2550mbar - so yes - the ECU does see a pressure deviation... when running more than 2550mbar by tweaking the n75 linearization table as Tony mentioned, the ECU is unaware of any pressure deviation (it sees 2550 regardless if your boost is 26 or 30PSI), as long as the deviation is over 2550mbar. As for boost ramp up, the N75 is always going to be slower to build boost than a ball and spring MBC - so you're going to build boost only as fast as the N75 will allow, and when the N75 attempts to build more boost than the MBC is set for, the MBC will take over bleeding boost pressure to open the wastegates, to lower the boost. If you're running less than 1.5 bar and have overboost issues, that really needs to be addressed with the tune - not with an MBC - otherwise the MBC is just a safety net for overboosting when running more than 1.5 bar since the ECU has no feedback and the PID is essentially useless when the map sensor is maxed out. |
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« Last Edit: October 12, 2010, 11:00:13 AM by Tony@NefMoto »
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iznogoud
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« Reply #14 on: October 11, 2010, 11:38:06 AM »
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Jason, you are correct on all regards. The N75 typically runs at 95% duty when trying to ramp up boost quickly. This means that it is open 1/20th of the cycle to bleed boost. The MBC is 100% when the ball is against the inlet, for sure. It makes sense that it would bring up boost faster. I did not expect the 1/20th to be that different, but I guess it depends on other things that allow the turbos to spool up fast, like turbo inertia (K03s spin easier than K04s) and down-pipe back-pressure. That is why tunes really should be custom for all hardware in order to work the best, but that is a side comment.
Also, since the MBC is effectively an on-off switch for boost, I would expect some minor wiggles similar to what we see with PID control and the solenoid (N75) regulation. I do not think there is a way around that. But Ihave seen FATS logs of stage 3 cars that bring up the boost and peg it at 22 psi. If there were any wiggles, the MAP sensor would pick those up. I guess those are tunes with lots of revisions to account for the hardware and have a "good" N75 duty map at WOT. For my stage 1 car, I am not looking for anything that "exact."
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