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Old 11-30-2008, 11:34 PM   #1
Tronner
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Default Why pull wastegate duty with low intake temps?

I'm just curious - I pulled some logs today, and my intake temps were 44 degrees or so. Boost was hitting about 14 psi when it was just tuned to hit about 17 psi on the dyno. However, the logs for the dyno showed intake temps of about 85 degrees.

In the Wastegate Compensation for intake temp table there is a -17.2 value for intake temp of 50, and -35.9 at 32 degrees.

I thought our cars liked the cold air, and running at least target boost, if not more would be OK? What other reasons am I missing for not running as much boost when intake temps are colder?
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Old 12-01-2008, 12:46 AM   #2
wrxsti.l
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To my understanding, as the temps decrease, you don't use as much WGDC to achieve the same boost. So if you were to set WGDC to 90% during tuning, when it is colder, you may only need to use 88% WGDC to achieve your targets, and if it uses the full 90%WGDC as set you'll exceed your targets - that is why there is the IAT compensations, to keep boost consistent during different temps.

There are a couple of reasons that I can think of as to why your boost is actually lower (instead of higher) with the cooler air temps. You may have exceeded your targets and your TD has caused psi to drop lower then normal, or your wastegate comp (air temp) map is causing it to run less boost during cooler temps.

What you need to do is log primary WGDC target boost, relative manifold pressure, throttle, engine speed and TD int and TD prop and IAT so ppl can have a look and see what is going on, rather then guess

Do a 4th gear WOT log from 2000rpm-redline logging those parameters I mentioned and post a link to the csv file here and I'm sure someone will be able to asist further.



FWIW my wastegate comp (air temp) map has -9.4 at 50 deg F and -18 at 32 deg F, which are less then what you have. But don't just use my settings - make sure you do a log as I have suggested and more suitable values will be suggested for your particular vehicle and location.
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Old 12-01-2008, 09:32 AM   #3
Tronner
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Thanks!

I will try to pull a log tonight and see what happens
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Old 12-01-2008, 10:45 AM   #4
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Colder air is denser.More molucles per volume going into the compressor.
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Old 12-01-2008, 01:20 PM   #5
Tronner
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I definitely get the denser air part, which would normally account for overboosting when it's colder, but shouldn't I be safe getting it to hit target boost? I guess I am asking as long as it is not OVERboosting, isn't it OK?
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Old 12-01-2008, 04:46 PM   #6
quazimoto
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Sounds like you wastegate compensation per IAT is alittle off.It happens.It's hard to tune for that when your getting a custom tune in much higher ambient temps.They are basiclly guessing how much compensation to use.Call your tuner and maybe he will retweak it for you.
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Old 12-02-2008, 11:49 AM   #7
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i'd just change/tune it yourself.

most tuners dont deal with all the different comps much since they are tuning inside usually between 60-90*.
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Old 12-02-2008, 07:45 PM   #8
Tronner
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I am fiddling with it myself. My first thought was to take the 50 and 32 degree wastegate compensation values (-17.2 and -35.9 respectively) and cut them in half, log again, then adjust again. The runs I logged above when seeing that boost had dropped off were 3 psi lower than target, and at about 44 degrees F.

I am enjoying learning more about how to mess around with this thing - but I have a LOT to learn!
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Old 12-02-2008, 07:47 PM   #9
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Oh, and it also looks like the same exact values are in the TD Prop, TD Integral Pos and Neg intake compensation tables. I assume I need those values to match whatever I set in the wastegate compensation map?
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Old 03-06-2010, 09:14 PM   #10
gungaslow
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did you find a solution as to what was going on??? how diid you fix it???
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Old 03-07-2010, 11:47 AM   #11
Tronner
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PM'd - yes, it was all in the tuning - Intake temp compensations were just pulling too much duty cycle
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Old 12-13-2013, 04:34 PM   #12
drogos
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looks like I have the same issue. I am running crazy low boost at low temps. I am on stage 1 so I am usually at 14 psi. Couple days ago IAT where around 10 and I would barely hit 11. I have attached screen drops for reference. Any hints highly appreciated. As OP suggested I am thinking about cutting those values by half and go from there but my questions is can I adjust just boost targets and WG for IAT and leave everything else untouched ?
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