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Can't keep boost at 0.9 - 1.0 bar

Vovan

By Vovan,
in Engines & Forced Induction

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Vovan Enthusiast

Vovan

Posted
Posted

I'm using APEXi AVC-R to control boost and SAFC to control fuel mixture, have stock turbo and stock intercooler. But i can't keep my boost even at 0.9 bar... first gear - boost go to my target 0.9 bar, then i switch to second gear there is a huge spike happens up to 1.05-1.1, and then pressure goes down and down while the revs go higer, the most drop happens at 6500 - 7000 revs, i can't even keep my boost at 0.7 on the second gear. then i switch to third (spike again) - same situation but boost is a bit higer - it stays at 0.7 - 0.8 bar. and goes down with revs going higher. forth gear is awesome - first is a small spike then boost goes down abit up to -0.05 bar from the target and then it goes up to 0.9 and stays there...

so, what i can't understand is what is the difference between revs at 2nd, 3rd and 4th gears? why i can't keep boost at 2nd and 3rd, but it's ok on 4th? is it i should configure AVC-R somehow more complex? i tried to make rev specific map for boost and make higher boost at 5500 - 7000 revs than it should. but there is still a drop :P

did anyone have such problem?

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https://www.sau.com.au/forums/topic/22990-cant-keep-boost-at-09-10-bar/
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gtrhybrid Contributor

gtrhybrid

Posted
Posted

Its not that the turbo wont hold boost at a high rpm, its that the turbo is SUPERHEATING the air at high rpm which looses major hp and is also why people upgrade to a bigger turbo. And when you boost 12 psi then it drops down one or two its called boost spike, caused by long boost lines to the waste gates or inacurate boost controller.

Merli Grand Master

Merli

Posted
Posted
Originally posted by Robo's

On my dyno runs, i peaked at 12psi, but gradually went down to 10psi by 7000rpm.

Apparently its the ineffeciency of the stock turbo.

I ran 14.5psi all day, everyday on my stock R33 GTS-t turbo.

AVC-R... 1 bar... No spiking.

Every gear held 1 bar if I'm not mistaken, perhaps 1st gear didn't quite get upto 1 bar, but I'm not sure as I never looked... I *AM* sure that 2nd, 3rd, and 4th held 1 bar perfectly all the way to the redline.

Whoever told you that is mistaken.

Vovan, you either have a vacuum leak somewhere along your boost controller/wastegate line, or your AVC-R isn't setup properly. Check to see that Gear-based learning isn't turned on too, that can sometime stuff up. Basically take it back to whoever set it up, and kick their ass :P

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