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Discussion Starter · #1 ·
Guys,

I just installed a Autometer 3301 boost gauge.

Having a few problems with the readings.

MY02 Wagon

19Hg Vacuum at Idle.
25Hg Vacuum on decel
Max boost reached in 1st gear is 11psi
Max boost reached in 2nd gear is around 12psi
Max boost in all other gears is around 13psi.

Can anyone please sanctify these readings

The car is bone stock.

I've connected my plumbing into the purge valve line on the manifold. Uts the nipple right next to the +ve wire that joins to the alternator witht eh REd cover cap.

I figured I should be getting higher reading than this?

Have I got a leak in the plumbing? If so how do I test it.

See picture for tap point!

Thanks in advance,
Antony
 

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AntMan said:
Guys,

I just installed a Autometer 3301 boost gauge.

Having a few problems with the readings.

MY02 Wagon

19Hg Vacuum at Idle.
25Hg Vacuum on decel
Max boost reached in 1st gear is 11psi
Max boost reached in 2nd gear is around 12psi
Max boost in all other gears is around 13psi.
..
Exactly what I saw on a bone stock WRX, except I would get momentary spikes to 15psi but it would always settle at around 13. I was tapped at the BOV.

-Pace
 

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Discussion Starter · #3 ·
Marvellous.

Now all is left is to match some mods so those numbers are a bit higher ;)

Thanks for the response Pace!

Cheers
Antony
 

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on a similar note, what is our stock wastegate spring set at?

when i step on it and the needle comes out of vacuum even if i hold the throttle steady, the needle drops down to vacuum again. doesn't that mean the wastegate opened and echaust stopped spinning the turbo?

i always figured the boost would hold as long as my throttle position would stay constant, then if i released throttle, the boost could go to vacuum.

any help?

dR
 

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Same numbers as far a vacuum, but with the Monkey I'm hitting 13 in first and 15 for the rest. Accelaration is alive and kicking.

I love my Monkey
 

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dark_rex said:
on a similar note, what is our stock wastegate spring set at?

when i step on it and the needle comes out of vacuum even if i hold the throttle steady, the needle drops down to vacuum again. doesn't that mean the wastegate opened and echaust stopped spinning the turbo?

i always figured the boost would hold as long as my throttle position would stay constant, then if i released throttle, the boost could go to vacuum.

any help?

dR
Not sure I can provide satisfactory answers, but here's some input.

I believe the stock wastegate spring is rated at something like 9psi. I think your boost reading is dropping into vacuum because your motor is not under enough load to build any boost, after the vehicle has reached the constant or equilibrium velocity dictated by the throttle position. You would either need to put the motor under further load from (a) accelerating, (b) increasing your speed to the point where the motor has to work harder against drag, or (c) drive up a gradient in a high enough gear to lug the motor.

I would _guess_ the dynamics of this are something along the lines of the following: Yes the compressor is spinning, but the flow of exhaust gas lacks the energy needed to spin the turbine with enough force to increase manifold pressure over that created by normal induction. i.e. What happens if you suck air with great force through a weakly powered fan? The spinning fan blades will provide a negligible effect on the pressure differential across the fan body. I don't believe the wastegate is playing any role whatsoever in this phenomenon. Its boost threshold is not being reached.

-Pace
 

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pace said:


Not sure I can provide satisfactory answers, but here's some input.

I believe the stock wastegate spring is rated at something like 9psi. I think your boost reading is dropping into vacuum because your motor is not under enough load to build any boost, after the vehicle has reached the constant or equilibrium velocity dictated by the throttle position. You would either need to put the motor under further load from (a) accelerating, (b) increasing your speed to the point where the motor has to work harder against drag, or (c) drive up a gradient in a high enough gear to lug the motor.

I would _guess_ the dynamics of this are something along the lines of the following: Yes the compressor is spinning, but the flow of exhaust gas lacks the energy needed to spin the turbine with enough force to increase manifold pressure over that created by normal induction. i.e. What happens if you suck air with great force through a weakly powered fan? The spinning fan blades will provide a negligible effect on the pressure differential across the fan body. I don't believe the wastegate is playing any role whatsoever in this phenomenon. Its boost threshold is not being reached.

-Pace
very helpful, pace. thank you. just one question. even if i'm really on it in third or fourth gear, say at 11psi and climbing, the wastegate is already allowing some exhaust to pass? would it be stupid to get a higher rated wastegate spring to allow boost to continue to build longer? wouldn't that allow boost to build faster up to the limit (past 9psi anyway)?

dR
 

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dark_rex said:


very helpful, pace. thank you. just one question. even if i'm really on it in third or fourth gear, say at 11psi and climbing, the wastegate is already allowing some exhaust to pass? would it be stupid to get a higher rated wastegate spring to allow boost to continue to build longer? wouldn't that allow boost to build faster up to the limit (past 9psi anyway)?

dR
Although your wastegate is rated to 9psi, your boost controller is bleeding off the boost signal such that the boost threshold is raised above and beyond the 9psi wastegate rating. Whether your wastegate is bleeding off boost at 11psi under acceleration in 3rd or 4th gear would depend if you are using ECU-controlled boost with a map that is setup to increase the boost gradually. However, let's assume you are just using an MBC set at a 15psi peak. If this is the case, there should be nothing bleeding through the wastegate at 11psi regardless. The wastegate should only bleed boost when instructed to do so with a 9psi signal. The boost controller is effectively 'hiding' this signal from the wastegate.

A higher rated wastegate spring would lessen the likelhood of the wastegate unintentionally bleeding off boost, but would in-turn decrease it's sensitivity and increase the likelyhood of spiking I think. It's interesting that you mention this because Phast and I were discussing ways to increase the tension on the VF30 spring due to a perception we have that it may not be holding boost well up around 18psi (at this altitude). He mentioned adding washers [to the spring] to exact the same effect.

-Pace
 

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So in essence, I think a higher tension wastegate spring should have no effect whatsoever on the _rate_ at which you can build boost. I believe it would however increase your peak boost setting, or in the case of the ECU-controlled boost it would shift the entire map upwards. (Since more boost signal is required to open the wastegate). The tradeoff being delayed response = more spiking.

-Pace
 
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