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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 > Cobb AP Boost Too High



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      05-01-2011, 03:52 PM   #1
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Cobb AP Boost Too High

My car is stock auto. In Florida weather on the 93 octane map the AP shows up to 16.5 held psi on WOT, is this too much for a car that is stock other than the Cobb?

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      05-01-2011, 03:54 PM   #2
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Yes if its sustained boost..if its just peaks then no.
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      05-01-2011, 03:57 PM   #3
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No, its sustained boost, it peaks at 21 psi.
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      05-01-2011, 04:01 PM   #4
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Holy Shit.that's way to high..post a log and email Cobb something isn't right
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      05-01-2011, 04:03 PM   #5
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The reading is based off of the Cobb AP unit, not a boost gauge.
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      05-01-2011, 04:05 PM   #6
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Cobb targets a load so if it thinks you need 16 PSI to hit load it will.

I think its too high personally unless you have full bolt ons.

Only way to verify is to see a log though as boost is only half the story. Might be partial throttle closure.


Might want to try 91 octane map its a little more conservative.
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      05-01-2011, 04:06 PM   #7
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So do I run the 91 octane map?
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      05-01-2011, 04:09 PM   #8
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Alright, I will get a log up as soon as I can.
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      05-01-2011, 04:14 PM   #9
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That will cause some serious issues down the road..the tuning may be sound but the hardware will wear out a crap load quicker...and for example I run 93 with fmic,dci,3 inch cp with awe bov's and I autotune to 14...16.5 and 21 peaks are not good for the turbos at all
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      05-01-2011, 04:18 PM   #10
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You guys need to realize. (Ive said this so many times) the PEAK BOOST numbers are inflated.

They are not pressure levels in the manifold or engine.

They are inflated because the throttle closes and creates turbulence where boost is read at the TMAP, pre throttle body.

This is why logs are crucial to understanding, not only for boost, and throttle, but ignition timing as well as fuel.
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      05-01-2011, 04:24 PM   #11
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Post a log showing it held 16.5, don't believe it did...must've been a shift spike
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      05-01-2011, 04:27 PM   #12
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I am going to try to have a log up by tonight.
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      05-01-2011, 05:33 PM   #13
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It is not a shift spike, mine would gradually Build boost upto 16 to 17 psi at around 4200 rpm then gradually taper back to around 13 or so at redline. The 21 psi would be the shift spike though.
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      05-01-2011, 05:38 PM   #14
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Yes but how long does the car actually sustain those boost numbers? Need to see logs to tell the full story.

Alan
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      05-01-2011, 05:42 PM   #15
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and this is only stage1? i can only image what a stage2 boost would be during hot weather
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      05-01-2011, 05:46 PM   #16
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Mid-range boost will be higher. It should taper down to 13 at redline.

Mid-range is has the largest Torque, and by no accident lowest ignition values. ITs the "hottest area".
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      05-01-2011, 06:23 PM   #17
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i've also noticed abnormallly high boost on WOT pulls w/ the cobb AP. i couldn't get the RPM's to scale on this log correctly, but this is a WOT pull in 2nd gear.









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      05-01-2011, 06:24 PM   #18
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Where the boost spike is in that graph also has huge throttle closure.

Did you feel it? (most people dont).

Again, these measurements of boost are NOT in the engine.
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      05-01-2011, 06:27 PM   #19
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Quote:
Originally Posted by Jeff@topgearsolutions View Post
Where the boost spike is in that graph also has huge throttle closure.

Did you feel it? (most people dont).

Again, these measurements of boost are NOT in the engine.
no, i couldn't feel the closure on this run or others that the logs indicated throttle closure. i know this is off the tmap sensor (not the intake manifold), it's just a little unnerving to see the boost jump up like that. i may switch down to the 91 octane maps, even though there isn't any sign of knock.
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      05-01-2011, 06:32 PM   #20
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Below was with Cobb V2.01/93, dynoed earlier.



Right now I'm running on 2.02/STD, much smoother now. I really love it.
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      05-01-2011, 06:35 PM   #21
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Quote:
Originally Posted by bryce View Post
no, i couldn't feel the closure on this run or others that the logs indicated throttle closure. i know this is off the tmap sensor (not the intake manifold), it's just a little unnerving to see the boost jump up like that. i may switch down to the 91 octane maps, even though there isn't any sign of knock.
You shouldnt feel it. The way the Cobb functions is similar to the how the stock DME controls boost. Which is using throttle to ward off excess boost when the wastegates arent responding fast enough.

Tunes like the PROcede control the wastegates a little better to reduce this effect.

Its 2 ways to do the samething.

As I always say tuning is an art and a science.
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      05-01-2011, 07:30 PM   #22
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I also see around 15-16 PSI sustained boost. I don't think this is good for the longevity of the turbos at all. I also had limp mode with misfire on cylinder 6 just today after a redline pull...
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