Higher Temp, Less boost - Subaru WRX Forum
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post #1 of 9 Old 12-31-1969, 07:00 PM Thread Starter
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I'm no expert here,.. but temperature will definately effect your boost. Colder air is denser to begin with right ? :wink: With an MBC you definately need to monitor your boost levels at all times but especially when there are temperature changes.
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post #2 of 9 Old 12-31-1969, 07:00 PM
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I don't think that hte air temp should make a difference for a manual boost controller, it works on pressure only. The colder air is more dense, which means more air will be moved into the intake at the same pressure, but that shouldn't effect the boost pressure seen. The way a MBC works is to bleed off controlled amounts of pressure to the wastegate, which effectivly tricks the wastegate into tripping at a higher compressor outlet boost pressure.

I'm not sure why your boost pressure would all of a sudden drop. Do you have a boost leak somewhere? Could the boost gauge of been adjusted? Maybe try to readjust your boost to 16.5psi, and see if it stays at that boost when the temps change. If it keeps on shifting with temp it might be a bad seal on the MBC.

Let me know what you find, I'm kind of curious.
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post #3 of 9 Old 12-31-1969, 07:00 PM
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I have only heard that there are some problems with the TurboXS unichip's ability to adjust to different air temperatures. The problem might be in the unichip trying to adjusted the MAF sensor to compensate for the temp change but you got me. Call Mark.

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post #4 of 9 Old 12-31-1969, 07:00 PM
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temperature can effect your boost pressure a little bit, like maybe .5 psi, but it shouldnt make a 1.5psi difference
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post #5 of 9 Old 12-31-1969, 07:00 PM
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TurboXS began including a ABC(auxillary boost controller) in there kits a few months back to aleiviate this problem. Basically it is just a boost bleeder between the turbo and factory BC solenoid. Call Mark and he'll give you one if you have TXS Unichip. Also they did some revisions to the stage2 maps.

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post #6 of 9 Old 12-31-1969, 07:00 PM
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Thats the problem with bleeder type valves. They will react like that to temp changes. However a good ball n spring MBC will stay more steady regardless of the temps.

Another thing to consider is when air heats up outside, you intercooler becomes less efficient and you will see a bit more pressure drop across the core.

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post #7 of 9 Old 12-31-1969, 07:00 PM
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My boost too has dropped a lot since the warmer weather has come in. Mine also dropped from 16 psi to 14.5 psi. I currently have a solenoid configuration to toggle between the factory boost controller and the MBC. I also have a needle valve (that is barely open) right before the wastegate. I have read that the MBC without a needle valve will force the wastegate to open quickly at your set boost and then drop off dramatically. That's the reason I put in the needle valve to bleed a little pressure and keep max boost steady. So should I: a) ditch the needle valve and run just the MBC on the high side of the solenoids so temp. changes wouldn't affect the boost level, or b) crank the needle valve open just a touch more when the outside temp. rises? BTW, the max boost with the FBC is also lower during warmer weather because of the needle valve.
Phast: You are running just a MBC right? Does your max boost remain solid to redline? Mine does now with the needle valve in place, but I haven't tried it without the needle valve.
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post #8 of 9 Old 12-31-1969, 07:00 PM
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Yea, it has gotten up into the 80's here in Arkansas and I have noticed that my boost has dropped too. The air Temps have a big to do with your current boost pressure. When it is colder outside the air is more dense and with your intercooler, it makes it colder with the windchill on it. This will make it even more dense than that was originally pulled in at the air box. Thus, more boost and more HP. Now when it starts to get warmer out, boost pressure will drop and so will your overall HP. The air is less dense and even with the IC, you can't get your intake air temp lower than what it could be when its colder outside. If you want to get a cooler IC temp during the higher heat, try getting MRT's IC water spray kit. This will spray a fine mist dispersing the heat better and making your IC cooler. Turbo's and IC's love the cold, damp and humid air! The engines love it even more! Hope this helps....

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post #9 of 9 Old 12-31-1969, 07:00 PM
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Higher Temp, Less boost

I noticed something odd today. Since I put the stage II on it's been cool with a high in the 50's. Today it is mid 70's and I noticed my boost is only 14 whereas in the cooler weather it was 16.5 dead on.

Anyone think it's odd my boost swung like that overnight, I would assume it's because of the different temps and air density but just wanted to toss it out for anything I might be missing.

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