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Passenger 57 09-08-2008 02:13 PM

Boost Gauge Questions...
I installed a autometer phantom II vacuum/boost gauge on saturday and was wondering what kind of readings should I be getting? I have a 99 9-3 SE HOT with the stock T25

I installed new plugs, and tapped the BPV vacuum line which I replaced with 4mm silicone hose.

When I start the car the gauge shows around 17in HG of vacuum, it seems that I really have to accelerate to get the car to boost past 0 psi.

Driving on the highway I hit it pretty hard and it boosted to around 10 psi, but when I get off the gas the gauge reads around 20-25 in HG, is that normal?

If the gauge is functioning properly, it seems that when city driving, the car spends most of its time in vacuum...

What do you think??? Are there any alternatives to the crappy plastic vacuum line you get with the gauge?

Palmer 09-08-2008 02:17 PM

That sounds somewhat normal to me. What turbo do you have?

The turbo needs exhaust gasses to spool up, so you need to accelerate to get PSI.

Make sense?

drewz airflow se 09-08-2008 02:20 PM

What year 9-3?

Palmer 09-08-2008 02:21 PM

Der, never mind.

Your peak boost seems a little low, like 2-3 PSI.

Other than that, it sounds fine.

Passenger 57 09-08-2008 02:31 PM

Time to slap on the MBC+A and see what happens

wasaaabi 09-08-2008 03:05 PM

if you have a mechanical boost gauge, it's possible that somewhere between the t fitting and the gauge, your line might be kinked. you could be seeing that 10psi on the highway because the pressure behind the kink is pushing it 'straight,' so to speak. If it's electrical, then a bad ground on the sender might be your problem... or it could be the sender wire is shorting to ground. I say go with the electrical if you have a mechanical and it's not too late to return it. Less problems. Hope this helps.

PoisonBeef 09-08-2008 05:12 PM

I have a non-hot and I see about those readings. On a good day with a hard pull she will hit 14psi, but settles around 10-12.

Remember 1st and 2nd gear are limited to 7psi or so while the rest are more.

Passenger 57 09-09-2008 07:01 AM

I forgot about the boost limit in 1st & 2nd :(

Adrenaline406 09-09-2008 09:27 AM

Sounds perfect, i sit at about 19 mm hg at idle. MBC will get you boost faster too ;D

93nut 09-09-2008 12:09 PM

hg is always less when the engine is cold or at a high altitude during idle. When the engine is warmed up the hg should be around 18-20 vacuum at idle.

PoisonBeef 09-09-2008 05:09 PM

I get 18hg at idle, 20 during engine braking.

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