Underboosting 1psi when hot only - anyone experienced this?

Asbjorn

Lieutenant
Mar 10, 2018
854
602
0
European, based in China
Ride
Z4 N54 DCT
So my car seems to have developed a problem where wgdc starts to oscillate and boost drops by around 1psi at higher rpm when hot. The problem disappears after a few hours of cool down. Has anyone experienced anything similar?

My mechanic suspects the turbo vacuum actuators which may leak when the turbos are hot only. Not sure if this is possible? I also guess it is hard to properly leak test them cold vs hot? @Chris@VargasTurboTech

I have divided into hot and cold logs below. Each pair of logs were done with identical hardware and fuel. No adaptations reset in between.

When I write hot below, it means the car has been driving at normal operating temps for a good amount of time. By cold I mean the engine has just finished warming up, and the oil temp needle has started to move. Transmission and other auxiliaries may not be super warm yet. So a typical cold scenario is where the car has idled in the workshop for a few minutes, and then driven to the test strip around 10mins away from the shop. A typical "hot" scenario would be where the car has been driven for at least one hour, and where the turbos have already been exercised a bit on the way.

Logs posted below.

Here's an overview of mods on the car. Boost solenoids are less than one year old. So are vacuum lines. Brake booster is 10 years old and may be leaking a tiny bit; Brake pedal sometimes goes stiff after parking for a few hours.

mods.jpg
 
Last edited:

Asbjorn

Lieutenant
Mar 10, 2018
854
602
0
European, based in China
Ride
Z4 N54 DCT
Today when cold (evening)

 

Asbjorn

Lieutenant
Mar 10, 2018
854
602
0
European, based in China
Ride
Z4 N54 DCT
Today when hot (afternoon)

 

Asbjorn

Lieutenant
Mar 10, 2018
854
602
0
European, based in China
Ride
Z4 N54 DCT
Four weeks ago when cold

 

Asbjorn

Lieutenant
Mar 10, 2018
854
602
0
European, based in China
Ride
Z4 N54 DCT
Three weeks ago when hot

 
Oct 24, 2016
1,152
1,202
0
45
Scottsdale, AZ
It could depend on many different variables, tune chief among them. First thing I'd do is ditch the oem airbox and give it a log. Have anyone near you that could let you try out DCI's for a cold/hot log comparison?

As for actuators -not likely. You *could* test them hot but it's going to be a pain in the ass to do so and IMO 100% not worth trying.

Chris
 

doublespaces

Administrator
Oct 18, 2016
9,303
4,331
0
AZ
Ride
2009 E93 335i
Take a look at the WGDC on this log compared to yours:


I'm not sure how big of a deal that is but your seems to be a bit jittery. What has your tuner said?
 

Asbjorn

Lieutenant
Mar 10, 2018
854
602
0
European, based in China
Ride
Z4 N54 DCT
Take a look at the WGDC on this log compared to yours:


I'm not sure how big of a deal that is but your seems to be a bit jittery. What has your tuner said?

My tune has never had a smooth wgdc like that, nor has load target ever been reached with any revision like yours. But it definitely gets more jittery when there are boost leaks. I don't know if that tells us anything.
 

Asbjorn

Lieutenant
Mar 10, 2018
854
602
0
European, based in China
Ride
Z4 N54 DCT
It could depend on many different variables, tune chief among them. First thing I'd do is ditch the oem airbox and give it a log. Have anyone near you that could let you try out DCI's for a cold/hot log comparison?

As for actuators -not likely. You *could* test them hot but it's going to be a pain in the ass to do so and IMO 100% not worth trying.

Chris

Is it possible that when the silicone inlets become hot, they go softer and collapse a bit more due to the flow resistance of the stock filter and snorkel creating a vacuum? I actually just reinstalled the snorkel a month ago.

We just inspected the air filter today and half of it is dirty due to oil entering when there was no snorkel... Front inlets have also been covered in oil more than I would like to admit due to leaking fittings while changing oil cooler setups again and again. Still find it hard to imagine that their stiffness would vary so much from hot to cold though.

Anyway, should be easy to order a set of DCIs and test.
 

Asbjorn

Lieutenant
Mar 10, 2018
854
602
0
European, based in China
Ride
Z4 N54 DCT
The inlets are intended to be used with high flow filters (all silicone inlets are); the stock box absolutely is a restriction, the silicone inlets will just reflect that restriction, always best to remove restrictions when possible.

Just made a quick test today. Both you and my tuner have been suggesting DCIs. However the data I collected today shows that the stock airbox is sufficient at my power level. It seems boost and wgdc are about the same. If anything iat runs a bit lower with stock airbox, but I did mash the pedal earlier in the rev range on the DCI log...



IMG_20190924_153757.jpg
IMG_20190924_142357.jpg


An explanation as to why I am seeing these results, besides the low power, could be that I am already running VTT inlets. Other data I have seen compared stock inlets + box vs upgraded inlets + dci as they are typically installed together.
 
Last edited:
  • Like
Reactions: RSL

dcafs

New Member
Apr 27, 2019
8
1
0
Ride
2008 135i
Just made a quick test today. Both you and my tuner have been suggesting DCIs. However the data I collected today shows that the stock airbox is sufficient at my power level. It seems boost and wgdc are about the same. If anything iat runs a bit lower with stock airbox, but I did mash the pedal earlier in the rev range on the DCI log...

I agree, but you are running the Z4 stock box with a taller lid, so less restrction than on the 1 or 3 series stock box.
I reverted back to the stock box on my 135 and did notice about a small rise in duty cycle over the DCI's, but I prefer less cabin noise and cooler incoming air of the stock box.

I will be purchasing the Z4 box in order to scavange the lid.....thanks for showing that it is comparable to the DCI's in terms of WGDC.
 
  • Like
Reactions: doublespaces

Asbjorn

Lieutenant
Mar 10, 2018
854
602
0
European, based in China
Ride
Z4 N54 DCT
I agree, but you are running the Z4 stock box with a taller lid, so less restrction than on the 1 or 3 series stock box.
I reverted back to the stock box on my 135 and did notice about a small rise in duty cycle over the DCI's, but I prefer less cabin noise and cooler incoming air of the stock box.

I will be purchasing the Z4 box in order to scavange the lid.....thanks for showing that it is comparable to the DCI's in terms of WGDC.

Great point, and you're welcome. Still, results may vary. My car doesn't pull as much air as others running higher boost. Also I already have upgraded inlets. I believe @jts1981 has concrete data that shows upgrading inlets is beneficial on the Z4.

You can probably also find data that the Mr5 style inlet lowers wgdc on the 1/3-series. If you dont run aux oil/radiator you might want to look into that as an alternative.

Anyway, just for fun, next time I get a chance I will try and measure the M4 airfilter size. Thats a 500hp-rated oem inlet system.