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Author Topic: High WG cracking pressure (20psi+) part throttle torque control strategy  (Read 15946 times)
julex
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My car currently sports Tial 770s, 4" to 2.5" super smooth y-pipe, SRM ICs, large Bi-pipes (and soon RS4 intake with Hemi throttle), 2.8 heads and I am having hard time controlling part throttle torque delivery. The ECU is using 5120 hack with real load, no underscaling (which is probably why I am having the issues, underscaled tunes are less sensitive to over-TQ situations).More specifically the initial onset of part throttle torque overshots the target value by a lot due to lack of WGDC control with high racking pressure on wastegates - tial 770s in mildest set up effectively delivers minimum of 21-22psi without any wastegate activity.

The ECU tries to moderate boost by closing the throttle which eventually settles boost/torque on the level I originally requested via gas pedal but to get there I am first hitting much more TQ.

Say I press the pedal to deliver 50% TQ and I initially hit 16psi which after some internal battling gets moderated down to 8psi and that's what the ECU rides at to red line. The whole process takes ~1-2s to settle.


What are your tuning strategies, or at least suggestions, to moderate TQ delivery in this situation without WGDC involvement?

Are there any maps that similarly to boost maps define aggressiveness of throttle activity to reach desired torque/boost or am I doomed to approach this with KFWDKSMX map and what else?


Thanks!

« Last Edit: June 16, 2013, 03:57:21 PM by julex » Logged
nyet
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Are you seeing fast path torque intervention (ignition retard)?

I'm also curious how to accomplish this. Almost every "pro" tuned car i've driven with big turbos and tight wastegates suffer from very poor part throttle control-ability.

IMO the proper solution is wastegates that can open with much less pressure, but packaging restraints make that almost impossible (on the 2.7t at least).
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julex
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Are you seeing fast path torque intervention (ignition retard)?

I'm also curious how to accomplish this. Almost every "pro" tuned car i've driven with big turbos and tight wastegates suffer from very poor part throttle control-ability.

IMO the proper solution is wastegates that can open with much less pressure, but packaging restraints make that almost impossible (on the 2.7t at least).

I don't see timing retard.

I tried adjusting wastegates to something smaller but tial packages ones with spring that starts moving at about 18-19psi so it cannot be lowered below about 20psi as it needs some preload.
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Gonzo
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Are you having load intervention or just charge pressure intervention (aka overboost)?

You can use N75 and 1bar WG crack pressure if you want. Really simple and part throttle works fine with a big turbo. I've done it before.
You will have to rescale some hPa axises though.
« Last Edit: June 16, 2013, 08:01:30 PM by Gonzo » Logged
nyet
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Are you having load intervention or just charge pressure intervention (aka overboost)?

You can use N75 and 1bar WG crack pressure if you want. Really simple and part throttle works fine with a big turbo. I've done it before.


due to packaging restrictions, any wastegate(s) small enough to fit the stock 2.7t location(s) don't seem to want to hold pressure very well with cracking at 1bar.

Quote
You will have to rescale some hPa axises though.

Not sure I follow. Rescaling hPa internally in ME7 won't change a wastegate's cracking and holding characteristics
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Rick
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You need to ensure you are not getting are not getting any N75 duty request on part throttle with such high WG cracking pressure.

Rick
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prj
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N75 between 0 and 100% will make no difference whatsoever until 14-15 psi anyway.

You probably want to adjust FUEDK so that the ECU does not overshoot it's initial throttle control.
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silentbob
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Have a look at BGPLGU. You have to calibrate your "base boost pressure" right to get this properly working.
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prj
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Have a look at BGPLGU. You have to calibrate your "base boost pressure" right to get this properly working.

Pretty sure this does not exist in 551M and plgru_w = pu_w.
Besides, even if it was there, then from a quick glance I had a while ago, I don't see how calibrating this will affect this at all. Nothing you do to LDRPID is going to make a difference in this case.

The only thing you can do is with a stiff wastegate spring to lower filling is either close up the throttle or trigger the N249's.
IMO what needs adjusting is the filling adjuster, specifically the filling at a throttle position.
The throttle oscillation is the ECU incorrectly choosing the base set point, and the settling is the P controller working to equalize rl to rlsol.
« Last Edit: June 18, 2013, 05:30:14 AM by prj » Logged

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silentbob
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pssol higher than 95% base boost pressure will make the throttle pop open because that's the limit were the air charge is supposed to be controlled by boost control. Staying under this limit will have the throttle control things. The function is there to handle excatly these kind of problems. Even the stock cars have it especially in cold conditions.

 
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phila_dot
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pssol higher than 95% base boost pressure will make the throttle pop open because that's the limit were the air charge is supposed to be controlled by boost control. Staying under this limit will have the throttle control things. The function is there to handle excatly these kind of problems. Even the stock cars have it especially in cold conditions.

So vpsspls_w?
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prj
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We can talk niceties all day, fact of the matter is, BGPLGU is not used on 551M/551G and lots of other software. Code for it is missing as well.
plgru_w = plgu_w = pu_w there.
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prj
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And extrapolating on that - if BGPLGU is not there, then the only thing that can be done is tweaking KFVPDKSD and KFVPDKSE.
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phila_dot
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We can talk niceties all day, fact of the matter is, BGPLGU is not used on 551M/551G and lots of other software. Code for it is missing as well.
plgru_w = plgu_w = pu_w there.

In LDRPID, plgrus_w is KFDPLGU * KFWPLGTA * pu_w. Both maps are filled with 1's, so effectively you have plgrus_w = pu_w.

And extrapolating on that - if BGPLGU is not there, then the only thing that can be done is tweaking KFVPDKSD and KFVPDKSE.

This is what I was getting at with vpsspls_w.
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silentbob
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So vpsspls_w?

Yes.
If the base boost pressure is defined in BGPLGU or in LDRPID is not relevant. It's the same thing just another name.
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