Overboost during BC settling time: how much is acceptable?

Looking for an advise, how much overboost during stock BC settling time would be considering as OK.

I have up to 1.14 psi overboost (up to 19.4 psi) on 3400 RPM during WOT on 4th gear.

The problem that I can't adjust WD table without rescaling, as it has 3200 and 3600 RPM on Y axis, and I have just right boost on both 3200 and 3600 cells.

For example, having 50 initial WD cycle for a 3200, and 39 WDC for 3600, I cant lower anything there without lower my max boost at 3200 or 3600 rpm, which I do not want to do.

The question is: should i live with 1.4 psi boost fluctuation during settling time, (no knock caused) or i have to rescale initial wd table, to have on Y axis something like this:

3000, 3400, 3800, etc.

In this case i will have just right wd value for a 3400 rpm.

Attached screenshot of the log, just in case you will want to see it.

Ok, I'll try. But again, for 3200rpm I need to have about 90% to reach target boost. Looks like 3600 only will be redused from 90 to 75 or so, as I've never seen more then 60% there.

I also will lower TD integral positive..

I think 1.4psi overboost to 19 is too much. I'm a big fan of re-scaling the target boost table to provide both maximum spool in lower gears and maximum control in upper gears. I rescaled my BT table to have rpm values at 2000, 2250, 2500, 2750, 3000, 3250, and 3500.... then less resolution up top where it's not needed as much. This works great in conjunction with appropriate (not-inflated) boost targets.

I disagree with the approach of lowering the max WGDC. While that might solve this problem, it can serve to cap boost in lower gears.

I think 1.4psi overboost to 19 is too much. I'm a big fan of re-scaling the target boost table to provide both maximum spool in lower gears and maximum control in upper gears. I rescaled my BT table to have rpm values at 2000, 2250, 2500, 2750, 3000, 3250, and 3500.... then less resolution up top where it's not needed as much. This works great in conjunction with appropriate (not-inflated) boost targets.

 

I disagree with the approach of lowering the max WGDC. While that might solve this problem, it can serve to cap boost in lower gears.

Legend speaks the truth, do not reduce your max WGDC. Your Y-axis rpm targets need to change among others things(initial and td possibly). 1.4psi is way too much, especially in third. 4th and 5th gear would be even worst.

Tuning boost on a 5EAT is actually much easier than on a 5MT. Boost control is all about time and on a 5EAT, it takes almost the same amount of time to hit peak boost regardless of gear. This is due to the TQ converter slipping at rpms below 3500 rpm.

Reduce WGDC initial until you no longer overboost.

If you are using a map based on mine, make sure that you reduce both WGDC initial and WGDC max. The difference between max and initial need to remain unchanged.

mickeyd2005, I cant reduce WGDC without re-scaling, as 3200 and 3600 has never overboost. I just need a number in between.

I like Legend's advise, but will rescale initial WGDC. It will be much easier to control boost if i have 3000, 3200, 3400, 3600 rows on WGDC table.

What is BT ? target boost? if it is, it won't help for me: how target boost will help, if it is overboosting because of initial WGDC?

BTW, i've lowered max WDGC for 3200 and 3600 cells, no overboost anymore, but slower spool and less boost on lower gears.

Anyway, thank all of you for help and education :-)

Rescaling the table is a good idea so you should do that. Airboy's spreadsheet has a rescaler tab that will do it for you very quickly.

However, you didn't have to do that. You could have dropped WGDC initial at 3200 rpm and used TD Proportional to make up the rest at 3200 rpm then at 3400 rpm, WGDC would have dropped to the correct value when boost error went to zero.

I adjust the scaling of target boost and WGDC all the time especially on larger turbos where you don't need fine control between 1800-2400 rpm.

mickeyd2005, I see what you are saying now..

I will increase TD proportional to make up WGDC to get desired boost lower gear, but lower initial WGDC will limit boost at higher gears. Right? Hope so :-)))

I think I'll rescale WGDC just to learn how to do it and for overall control over the boost, but for sure I'll take your advice.

Thank you again!

mickeyd2005, I see what you are saying now..

I will increase TD proportional to make up WGDC to get desired boost lower gear, but lower initial WGDC will limit boost at higher gears. Right? Hope so :-)))

 

I think I'll rescale WGDC just to learn how to do it and for overall control over the boost, but for sure I'll take your advice.

Thank you again!

No. Don't adjust TD proportional. It's already set up.

The difference between WGDC max and WGDC initial will automatically work itself out. This is why I said to make sure that the delta between WGDC max and WGDC initial is the same as my original map (if you are using my TD tables).

Legend speaks the truth, do not reduce your max WGDC. Your Y-axis rpm targets need to change among others things(initial and td possibly). 1.4psi is way too much, especially in third. 4th and 5th gear would be even worst.

And here's why you don't want to reduce your max WGDC. Data taken from my car with VF40 this a.m. Look how dropping your max WGDC would clip WG duty and therefore boost in 1st and 2nd gears. (I know yours is the 5EAT, OP, but I assume this still applies).

http://www.beeez.com/lgt/wg316.jpg

Yes, I see, Legend.

I've using WGDC proportional from Myckey'd map, lowered initial WGDC. now car is hitting boost much faster,and holds it longer. I even need to adjust my timing/or target boost.

So, the key is a big numbers in WGDC proportional table.

I did not drop max duty, as you suggested.

In fact, I've increased TD integral cumulative range to 20, as 15 was not enough to cover diff between lower and high gear WGDC requred..

At spool up you do not need to do that as the proportional should still be being applied.

Yes, but what i've seen on a log, proportional was limited by max correction, which was 15%.. Despite max proportional for 5 psi boost error was 24%.

So, 20% max correction was just enough to get full boost at 1st gear, which I never seen before.

Only bad thing i've noticed is a huge overboost after I shifted from 4th to 3rd, during WOT, around 4800 RPM.. Boost jumped from 15 to 20.5, despite of wgdc went from 92 to 40. And it knocked, as you can expect..

Not sure what I can tune to fix this.. May be it will happen anyway when you downshift 5AT under WOT, without a throtle lift.

EDIT: "a huge overboost after I shifted from 4th to 3rd, during WOT, around 4800 RPM" should be read like this: "a huge overboost after I shifted from 2nd to 3rd, during WOT, around 4800 RPM."

Why is his overboost too much? Is it just too much for a VF40? If you had a target boost of 22psi on a 20G or GT30 would overboost of 1.4psi be a problem as well?

The air coming in is metered, and if the tune is good the AFRs will be fine. Is it just generating too much heat for a VF40, or is there some other reason why this is a problem.

Why is his overboost too much? Is it just too much for a VF40? If you had a target boost of 22psi on a 20G or GT30 would overboost of 1.4psi be a problem as well?

 

The air coming in is metered, and if the tune is good the AFRs will be fine. Is it just generating too much heat for a VF40, or is there some other reason why this is a problem.

Overboost is bad for a couple of reasons:

1. The car may not have been tuned for that load and it may be uncharted part of the map.

2. The overboost might be outside the efficiency of the turbo. If the VF40 could hit a higher boost, why not use it all the time?

3. Overboost causes TD integral to wind down causing a loss of power right after the overboost.

The reason I ask is that my car overboosts as well. My boost target is 22.5 psi (on a TD06-20G), and I will hit a shade over 23.5psi before my car settles at my boost target.

I tuned my car myself and there is no knock at all in any of my logs. I'm running very strong timing with meth and good gas with this boost target. Also my boost does not drop below my target after overboost. I personally don't feel my overboost is a problem at all, and I'm not worried about tuning it out.

Overboost is bad for a couple of reasons:

 

1. The car may not have been tuned for that load and it may be uncharted part of the map.

2. The overboost might be outside the efficiency of the turbo. If the VF40 could hit a higher boost, why not use it all the time?

3. Overboost causes TD integral to wind down causing a loss of power right after the overboost.