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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 06-09-2007, 10:54 PM   #1
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boost gauge pics and boost questions

pics will come shortly, gotta upload them. i ended up putting an autometer gauge in place of the light switch, took about an hour, wow, so simple, people should do that more!

so turns out my stock gauge aside from being slow isn't that bad, it consistently reads the first break as 0psi, the second as 10psi, and the end of red as 20psi.

anyhow, now that i can monitor boost better, a few questions.

in gears 3, 4, and 5 i spike at 19-20psi then it settles around 15-16psi in 3rd and 17-18psi in 4th, but in fifth it spikes at 3k rpm at 20psi, then holds solid for a while, then wavers between 17 and 20 psi back and forth like it wants to stay there? whats up with that?

also, sometimes in 2nd gear when i nail the gas, i get about 5psi until 4k rpm, then it'll kick up to 14 psi roughly, but not always will it hesitate... turbo dying?

thanks!
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Old 06-10-2007, 01:54 AM   #2
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It's hard to say what the pressure "should" be with a tuned ecu.

Look at a compressor map for a similar TD04 compressor side and probably what you're seeing is the compressor's ability to supply the requested mass flow, at whatever psi it works-out to be.

Your engine will outflow your turbo, when that happens you will see the manifold pressure will drop.

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pics will come shortly, gotta upload them. i ended up putting an autometer gauge in place of the light switch, took about an hour, wow, so simple, people should do that more!

so turns out my stock gauge aside from being slow isn't that bad, it consistently reads the first break as 0psi, the second as 10psi, and the end of red as 20psi.

anyhow, now that i can monitor boost better, a few questions.

in gears 3, 4, and 5 i spike at 19-20psi then it settles around 15-16psi in 3rd and 17-18psi in 4th, but in fifth it spikes at 3k rpm at 20psi, then holds solid for a while, then wavers between 17 and 20 psi back and forth like it wants to stay there? whats up with that?

also, sometimes in 2nd gear when i nail the gas, i get about 5psi until 4k rpm, then it'll kick up to 14 psi roughly, but not always will it hesitate... turbo dying?

thanks!
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Old 06-10-2007, 06:30 AM   #3
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Quote:
Originally Posted by Drew in Houston View Post
It's hard to say what the pressure "should" be with a tuned ecu.

Look at a compressor map for a similar TD04 compressor side and probably what you're seeing is the compressor's ability to supply the requested mass flow, at whatever psi it works-out to be.

Your engine will outflow your turbo, when that happens you will see the manifold pressure will drop.
His is t5 so no mass air request. Best to give your tuner a call and see what he says here. I boudt your outrunning the td04 at that amount of boost seeing as you can hold 18psi in 4th. Might possibly need a helper spring for the wastegate though. This sounds plausible to me because you say it fluctuates between 17 and 20 psi. Well if it holds 18 in 4th, and you normally spike 20 anyways..... Its basically dancing around that 18 number making me thing your wg is opening instead of staying closed.



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Old 06-10-2007, 08:19 AM   #4
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Hmm i'll look into that and so some research. As for e-mailing automotion about the tune, they are good and answer my questions but the answers are usually very complacent... "yeah that sounds normal. let me know if you want another tune" is kind of the name of the game there...

and I have the stock garrett t25 still.
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Old 06-10-2007, 10:14 AM   #5
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the answer is simple. The stock t25 turbo cannot produce enough airflow at higher RPM's to sufficiently hold 18psi. The tiny thing is trying its heart out though. That does sound about right though. Upgrade the turbo

edit: Your going out of the efficiency range with the t25, and maybe a bit of boost creep.

Last edited by Guteman; 06-10-2007 at 10:17 AM.
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