[lucasborka]

Hi!

I’m chasing an issue where the car overboosting right after going from 4>5 gear. I could feel it in the car when throttle closes and DV dumps slightly. The car will jolt

I have smoke tested with pressure multiple times and could not for my life find any leaks. It was leaking at intake connection down at the turbo but it is fixed!

Watergate position is also checked with Ista and it shows no issues

No codes no nothing.

Log: https://datazap.me/u/lucasborka/over...og=0&data=3-21

https://datazap.me/u/lucasborka/clos...ata=3-17-21-24

Hot idle log: https://datazap.me/u/lucasborka/hot-...og=0&data=3-21

BMW 435i FBO 2015
Catless
FMIC 5”
CP
Gfb DV+ without additional spring
MHD Stage 2+
XHP stage 3

[thejeremyman9]

Ironically i think that just happens sometimes when you have really good boost control. Here's some examples from my logs:

https://datazap.me/u/thejeremyman9/1...&data=4-5-7-17

https://datazap.me/u/thejeremyman9/d...=4-5-7-9-17-19

I think its happened less since i went down to XHP stage 2 but i havent logged 4-5 gear shift in a while.

[lucasborka]

Originally Posted by thejeremyman9

Ironically i think that just happens sometimes when you have really good boost control. Here's some examples from my logs:

https://datazap.me/u/thejeremyman9/1...&data=4-5-7-17

https://datazap.me/u/thejeremyman9/d...=4-5-7-9-17-19

I think its happened less since i went down to XHP stage 2 but i havent logged 4-5 gear shift in a while.

Oh alright! Yeah the boost seems to be 100% on point, which is good. And STFT in the ballpark

But did you ever feel the closure? I can clearly hear the DV dump and the car jolts.

If I go back to XHP stage 2 I never feels it

[LA1Z24]

After it dumps boost once in 5th, will it build boost in 5th again or is it flat till you change into another gear?

[lucasborka]

Originally Posted by LA1Z24

After it dumps boost once in 5th, will it build boost in 5th again or is it flat till you change into another gear?

It builds fast and pushes all the way to 8th

[LA1Z24]

So you shift into 5th, it dumps boost, but it will build boost again in 5th gear without shifting to a different gear first?

[lucasborka]

Originally Posted by LA1Z24

So you shift into 5th, it dumps boost, but it will build boost again in 5th gear without shifting to a different gear first?

Yes it build boost again instantly, the only difference is that you gear it dump fast and car jolts. Then continue as normal

I have only tried in manual mode and it doesn’t change gear. I’ll have to try in regular S mode

Super wierd issue

[thejeremyman9]

Originally Posted by lucasborka

Oh alright! Yeah the boost seems to be 100% on point, which is good. And STFT in the ballpark

But did you ever feel the closure? I can clearly hear the DV dump and the car jolts.

If I go back to XHP stage 2 I never feels it

Occasionally i can feel a slight loss of power for a split sec when shifting into the higher gears but its not really a strong jolt and it rarely happens. TBH i would just run stage 2 XHP. I switched back after the pure drivetrain article and i feel like there is no loss of performance and the car drives a bit smoother and more consistent.

MHD is very sensitive to overboost and quick to react if boost mani exceeds target (and relatedly if load exceeds target). Basically i think what is happening is when your boost control is so close to target and you shift quickly into a higher gear with more, the higher load pushes the boost over target right after the higher gear engages and what you feel/see in the logs is the reaction to the overboost.

[thejeremyman9]

Originally Posted by LA1Z24

So you shift into 5th, it dumps boost, but it will build boost again in 5th gear without shifting to a different gear first?

It doesn't really "dump boost" fully or anything, it just reacts to boost exceeding target my partially closing throttle and regulating the boost with the DV until you are back below target. But its not like its going back to zero boost then building back up, its more of a boost/load 'correction'

[lucasborka]

Originally Posted by thejeremyman9

Occasionally i can feel a slight loss of power for a split sec when shifting into the higher gears but its not really a strong jolt and it rarely happens. TBH i would just run stage 2 XHP. I switched back after the pure drivetrain article and i feel like there is no loss of performance and the car drives a bit smoother and more consistent.

MHD is very sensitive to overboost and quick to react if boost mani exceeds target (and relatedly if load exceeds target). Basically i think what is happening is when your boost control is so close to target and you shift quickly into a higher gear with more, the higher load pushes the boost over target right after the higher gear engages and what you feel/see in the logs is the reaction to the overboost.

Yeah it all makes total sense, I’ll have to run XHP stage 2 then. It is more smooth and consistent just as you experience 😀

Maybe I could benefit for a custom tune to eliminate this at stage 3 XHP. But I don’t want all the hassle 😂 I’ll have to accept that there is no issues with the car