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Old 01-13-2006, 03:49 AM   #1
moabrox
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Join Date: Nov 2005
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Aspen White

Default Boost Controller Question

I was just looking into boost controllers (before I got my accesport realized I needed EM first) and had a few unanswered questions to take care of. It is to my understanding that the boost pressure is regulated by 2 factors: Which gear your in, and RPM (please correct me if I'm wrong). This makes it almost impossible to hit peak boost in 1st or 2nd gear. Does a manual boost controller override the computers gear and rpm regulators, for instance, woulda manual boost controller make it possible to hit peak boost in first gear or even neutral? I'm not looking to increase boost pressure. Also I have an AP on stage 1 HWG and I'm hitting 17.5 PSI. Would a manual boost controller override the AP also example: if you set the boost controller on 13 would your peak boost be 13 or would the accessport take over and boost to 17.5?
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Old 01-13-2006, 01:31 PM   #2
bboy
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Boost is regulated by the energy in the exhaust, the amount the wastegate is open, and the amount of exhaust that can flow through your turbo housing.

Not enough exhaust flow-->low or no boost.
Wastgate closed-->uncontrolled boost
No boost control-->wastegate runs on spring pressure (~8 psi)
Not enough flow through the exhaust housing-->boost creep (boost rises, never holds steady)

You cannot hit peak boost in 1st gear because your boost control system cannot "bleed" enough boost off of the wastegate and so it blows open. It's as if you are running on "semi" spring pressure.

There a number of solutions to you needs: better solenoid for the stock system, manual boost controller, manual boost controller in conjunction with stock solenoid, separate electronic boost control.

To answer your last question, if you have a separate boost controller (not the stock) and set boost to a lower value than what the ECU is trying to achieve (your example 13 psi vs AP's 17.5 psi), then your boost will be 13 psi and the ECU will keep "trying" in vane to achieve 17.5 psi.
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Old 01-13-2006, 02:38 PM   #3
Underboosted
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^what he said...

and, on the other side of that, if you set the MBC for higher say...18psi, you will achieve it in every gear...

but never in nuetral
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Old 01-13-2006, 02:44 PM   #4
moabrox
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Default thanks

Hey, thanks alot guys, I don't want to hit boost in neutral just thought it might (in theory). But mainly I just wanted a little more in 1st and 2nd. thanks again.
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Old 01-13-2006, 02:57 PM   #5
Freon
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A blocking or interrupt style solenoid will pretty much allow you to build as much boost as you want, until the backpressure itself pushes the WG open. You only need enough time for the wheel to get up to speed, which still may be a problem in low gears unless you're traveling uphill or something. There's no need for an MBC bleeder with a blocking solenoid, because you can almost instantly have atmospheric pressure in the WG control hose.

An MBC bleeds off pressure to make up for the inability of the stock solenoid to bleed enough air fast enough. If you block, there is no flow limitation because charge air cannot get to the WG spring at all. The small volume of pressurized air that is there can easily dump when the solenoid energizes. The stock bleed solenoid has to bleed a constantly refreshing volume of air from the turbo compressor even when energized.

For the cost, and if you can retune your boost map (via UTEC, AP ST, pro tune, etc), I'd start with a new solenoid. It's about $40 for a GM setup and it takes 15 minutes to install, plus tuning time. Search for "gm solenoid full diy".
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