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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Boost Targets and Colder Weather



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      10-09-2008, 08:39 AM   #1
nj335i
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Boost Targets and Colder Weather

Here in NY/NJ, we've been seeing 50 degree lows overnight. I find that my car is only hitting 13psi when it is tuned for 15psi (Helix Attache). Not sure if it's my boost gauge that's off because I reset it recently though. I'm seeing -20 after the car is warmed up and idling, and that seems normal. Anyone else seeing lower boost in colder weather?
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      10-09-2008, 03:56 PM   #2
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      10-09-2008, 04:01 PM   #3
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-20 boost? I know NYC's been getting low 50s weather....here in houston, we get it down to about low 70s, high 60s and the car has been pulling strong nowadays
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      10-09-2008, 05:00 PM   #4
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Quote:
Originally Posted by darkphantom View Post
-20 boost? I know NYC's been getting low 50s weather....here in houston, we get it down to about low 70s, high 60s and the car has been pulling strong nowadays
-20 in vacuum

Just wanted to see if other members with tunes are seeing lower peaks due to cooler weather...
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      10-09-2008, 05:00 PM   #5
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Quote:
Originally Posted by darkphantom View Post
-20 boost? I know NYC's been getting low 50s weather....here in houston, we get it down to about low 70s, high 60s and the car has been pulling strong nowadays
I think he meant -20 "VACUUM" not boost. He is getting lower boost in the cold, but his vacuum is the same.
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      10-09-2008, 05:07 PM   #6
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is there anything wrong if i only see -10 vacuum?
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      10-09-2008, 05:23 PM   #7
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Quote:
Originally Posted by nj323ci View Post
I think he meant -20 "VACUUM" not boost. He is getting lower boost in the cold, but his vacuum is the same.


Alex, your car is looking great! It sure came along nicely!

End ing of my own thread.
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      10-09-2008, 05:27 PM   #8
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Seeing the same thing with JB3, though I don't trust my boost gauge. It's been sitting further and further below '0' as time goes on. I have to get around to getting my VEI in.

Honestly, it feels fast enough that I might not be having low boost, and the gauge might just be tricking me.
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      10-09-2008, 05:31 PM   #9
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Alex, your car is looking great! It sure came along nicely!

End ing of my own thread.
Thanks bro
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      10-09-2008, 07:45 PM   #10
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Quote:
Originally Posted by ontopofm View Post
is there anything wrong if i only see -10 vacuum?
I think -19 to -21 is the normal value of vacuum when the car is at idle...Are you seeing these values? If not you may have a crimp in the tube where it reads it pressure from.
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      10-09-2008, 11:03 PM   #11
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I see -21 vacuum @ idle, boost is about 1-1.5 psi lower on cold days ( 13.5 - 14 psi instead of ~ 15 psi ).
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      10-09-2008, 11:07 PM   #12
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Quote:
Originally Posted by cwn23 View Post
I think -19 to -21 is the normal value of vacuum when the car is at idle...Are you seeing these values? If not you may have a crimp in the tube where it reads it pressure from.
oh shiet, i only see -10 max
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      10-10-2008, 07:42 AM   #13
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Quote:
Originally Posted by ontopofm View Post
oh shiet, i only see -10 max
What is the scaling? -10 PSI or -20 inHG?

You may be reading in negative PSI and not the typical vacuum measurement of inches of mercury. The engineering units need to match.
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      10-10-2008, 07:55 AM   #14
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Could be due to the increased density of the air and ecu compensation.
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      10-10-2008, 08:26 AM   #15
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Quote:
Originally Posted by e.n335 View Post
I see -21 vacuum @ idle, boost is about 1-1.5 psi lower on cold days ( 13.5 - 14 psi instead of ~ 15 psi ).
Quote:
Originally Posted by bdkevoIX View Post
Could be due to the increased density of the air and ecu compensation.
So at least I'm not going crazy... But why wouldn't the tune take advantage of the denser air and still target 15psi in the colder weather?
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      10-10-2008, 09:28 AM   #16
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Quote:
Originally Posted by scalbert View Post
What is the scaling? -10 PSI or -20 inHG?

You may be reading in negative PSI and not the typical vacuum measurement of inches of mercury. The engineering units need to match.
I am pretty sure his guage reads psi...I think there has to be a crimp in his tubing!
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      10-10-2008, 09:54 AM   #17
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Quote:
Originally Posted by scalbert View Post
What is the scaling? -10 PSI or -20 inHG?

You may be reading in negative PSI and not the typical vacuum measurement of inches of mercury. The engineering units need to match.
mine is digital and it's only show the numbers, it's said on their website the reading range is -14 inHg ~ 45 PSI, so i guess the number is correct?

just got an answer from the Rep, it reads -psi during idle

Last edited by ontopofm; 10-10-2008 at 11:27 AM.
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      10-10-2008, 12:04 PM   #18
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Quote:
Originally Posted by ontopofm View Post
mine is digital and it's only show the numbers, it's said on their website the reading range is -14 inHg ~ 45 PSI, so i guess the number is correct?

just got an answer from the Rep, it reads -psi during idle
Just FYI, -10 PSI is about the same as 20 inHg vacuum so everythign is fine.
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      10-10-2008, 12:07 PM   #19
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Quote:
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So at least I'm not going crazy... But why wouldn't the tune take advantage of the denser air and still target 15psi in the colder weather?
Consistency in power; it is really a preference thing. Some enthusiasts would want to extract ever bit of power out of it. Whereas most want it to run the same from summer to winter. Large swings in power output often make people feel something is wrong with the car so the manufacturers try and keep the relative output equal in all weather conditions.
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      10-10-2008, 12:10 PM   #20
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Just FYI, -10 PSI is about the same as 20 inHg vacuum so everythign is fine.
thanks
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      10-10-2008, 02:56 PM   #21
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i thought boost goes up in colder weather? cooler air?

so boost drops in colder weather? rises in hotter weather?
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      10-10-2008, 03:44 PM   #22
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I think any tune referencing AIT will have lower boost in cold weather. I could be wrong though.
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